The Genus Pythium in Mainland China

The genus Pythium in mainland China

HO Hon-Hing*

Department of Biology, State University of New York, New Paltz, New York 12561, USA

Abstract: A historical review of studies on the genus Pythium in mainland China was conducted, covering the occurrence, distribution, taxonomy, pathogenicity, plant disease control and its utilization. To date, 64 species of Pythium have been reported and 13 were described as new to the world: P. acrogynum, P. amasculinum, P. b ai sen se , P. boreale, P. breve, P. connatum, P. falciforme, P. guiyangense, P. guangxiense, P. hypoandrum, P. kummingense, P. nanningense and P. sinensis. The dominant species is P. aphanidermatum causing serious damping off and rotting of roots, stems, leaves and fruits of a wide variety of plants throughout the country. Most of the Pythium species are pathogenic with 44 species parasitic on plants, one on the red alga, Porphyra: P. porphyrae, two on mosquito larvae: P. carolinianum and P. guiyangense and two mycoparasitic: P. nunn and P. oligandrum. In comparison, 48 and 28 species have been reported, respectively, from Taiwan and Hainan Island with one new species described in Taiwan: P. sukuiense. The prospect of future study on the genus Pythium in mainland China was discussed. Key words: Pythiaceae, taxonomy, Oomycetes, Chromista, Straminopila

中国大陆的腐霉属菌物何汉兴*

美国纽约州立大学纽约新帕尔茨 12561

摘要：综述了中国大陆腐霉属的研究进展，内容包括腐霉属菌物的发生、分布、分类鉴定、致病性、所致植物病害防治及腐霉的利用等方面。至今，中国已报道的腐霉属菌物有 64 个种，其中有 13 个种作为世界新种进行了描述，这 13 个新种分别为：顶生腐霉 Pythium acrogynum，孤雌腐霉 P. amasculinum，百色腐霉 P. baisense，北方腐霉 P. boreale，短枝腐霉 P. breve，壁合腐霉 P. connatum，镰雄腐霉 P. falciforme，贵阳腐霉 P. guiyangense，广西腐霉 P. guangxiense，下雄腐霉 P. hypoandrum，昆明腐霉 P. kummingense，南宁腐霉 P. nanningense 和中国腐霉 P. sinensis。瓜果腐霉 Pythium aphanidermatum 为优势种，在全国普遍引起多种植物严重的猝倒病和根、茎、叶、果腐烂病。其中，大多数腐霉种对植物具有致病性，44 个种寄生植物，1 个种：紫菜腐霉 P. porphyrae 寄生红藻和紫菜，2 个种：卡地腐霉 P. carolinianum 和贵阳腐霉 P. guiyangense 寄生蚊子幼虫，2 个种：努氏腐霉 P. nunn 和寡雄腐霉 P. oligandrum 是真菌的重寄生菌。相

*Corresponding author. E-mail: [email protected] Received: 11-02-2012, accepted: 18-12-2012 HO Hon-Hing / The genus Pythium in mainland China 21

比之下，台湾报道的腐霉种有 48 种（其中新种 1 个：四季腐霉 P. sukuiense），海南报道的腐霉种有 28 种。对中国大陆腐霉属的研究前景也进行了讨论。关键词：腐霉科，分类，卵菌纲，假菌界，茸鞭生物界

INTRODUCTION Nevertheless, recent phylogenetic studies based on The genus Pythium Pringsh., with 305 the molecular data have provided new evidence and described species (www.mycobank.org), has been rekindled interest to split the genus Pythium. Thus classified traditionally with other filamentous, Ko et al. (2010) erected a new genus coenocytic, sporangia-producing fungi as Aquaperonospora Ko for species producing rigid, “Phycomyetes” (Fitzpatrick 1930). However, with erect and branched Peronospora-like sporangiophores recent advances in chemical, ultrastructural and forming sporangia synchronously on branchlet tips. molecular studies, Pythium spp. are now considered Bala et al. (2010) proposed a new genus as “fungus-like organisms” or “pseudo-fungi” and Phytopythium Abad, de Cock, Bala, Robideau & are placed in the Kingdom Chromista (Kirk et al. Lévesque for those Pythium species in clade K of 2008) or Kingdom Straminopila (Webster & Weber Lévesque and de Cock (2004) that produce globose 2007), kingdoms distinct from the Kingdom Fungi to void, often papillate and internally proliferating (Moore et al. 2011). Historically, there has also been sporangia similar to species of Phytophthora de great confusion regarding the validity of Pythium as Bary. Subsequently, Hulvey et al. (2010) transferred a distinct genus. The genus was created by Phytopythium from Family Pythiaceae of Pythiales Pringsheim (1858) and placed in the family to Peronosporaceae of Peronsporales based on Saprolegniaceae. However, Pythium Pringsh. was molecular studies. Uzuhashi et al. (2010) restricted antedated by both Pythium Nees and Artotrogus the genus Pythium to those species with inflated or Montagne. Subsequently, the genus Pythium non-inflated filamentous sporangia while creating Pringsh. was conserved (Plaats-Niterink 1981). four new genera to accommodate species with non There were attempts to split the genus Pythium into filamentous sporangia: Ovatisporangium Uzuhashi, two genera to differentiate species with spherical Tojo & Kakish with mainly ovoid to pyriform, sporangia from those with filamentous sporangia. sometimes irregular shaped-sporangia, Schröter (1897) erected the family Pythiaceae in Elongiosporangium Uzushashi, Tojo & Kakish with which he described Pythium having globose clavate to elongate sporangia, Globisporangium sporangia and Nematosporangium (A. Fischer) Uzushashi, Tojo & Kakish with globose, sometimes Schrӧter with filamentous sporangia. On the other proliferating sporangia and Pilasporangium hand, Sparrow (1931) proposed species of Pythium Uzushashi, Tojo & Kakish with globose, with globose sporangia to be placed in a new genus: non-proliferating sporangia. While recognizing the Sphaerosporangium Sparrow. Others tried to create genus concept of Pythium is still in a state of flux, I various infrageneric taxa within Pythium but all prefer to adhere to the classical definition of these proposals have been rejected by Waterhouse Pythium to include all oomycetous fungi producing (1967), Plaats-Niterink (1981) and Dick (1990). non-deciduous sporangia only in water with variable

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shapes ranging from spherical, subspherical, ovate, This paper serves as a historical review of the obovate, ellipsoidal, pyriform to lobulated and genus Pythium in continental mainland China and its filamentous, with zoospores formed in a future prospects. Since extensive reviews of the membranous vesicle at the tip of an exit tube of the Pythium species were provided recently for Taiwan sporangium (Waterhouse 1974). (Ho 2009, 2011) and Hainan Island (Ho 2012) these In distribution, the species of Pythium are two regions have been excluded from this review but cosmopolitan, widely distributed throughout the the findings there will be used for comparison. world ranging from tropical to temperate 1 HISTORICAL REVIEW (Plaats-Niterink 1981) and even arctic (Hoshino et 1.1 Occurrence, distribution, taxonomy and al. 1999) and antarctic regions (Knox & Paterson pathogenicity of Pythium species 1973). They exist as saprophytes or parasites in soil, There is no doubt that it was T.F. Yu, Professor water, on plants, fungi, insects, fish, animals and of Plant Pathology at the University of Nanking, human beings (Yu 2001). Economically, they are Nanking who initiated and laid the foundation for especially important as pathogens of higher plants, the study of plant diseases in mainland China caused causing serious damage to agricultural crops and turf by Pythium species. In March, 1933 he noticed a grasses, leading primarily to soft rot of fruit, rot of serious damping off disease of cucumber in the hot roots and stems, and pre- and post-emergence of beds of the University of Nanking garden. The seeds and seedlings by infecting mainly juvenile or disease was very prevalent in Nanking and its succulent tissues (Hendrix & Campbell 1973). vicinity and he provided detailed description of the Whereas Pythium diseases are common in tropical to causal pathogen: Pythium aphanidermatum (Edson) temperate regions, cereal seedlings under snow Fitz. (Yu 1934). Subsequently, he found that the could also be killed by Pythium spp. (Hirane 1960; pathogen was widely distributed in China, attacking Lipps 1980) and an unidentified species of Pythium a wide variety of vegetables and fruits as well as isolated from a colony of diseased leafy liverworts other important crops like cotton and tobacco in the from Signy Island of Antarctic proved to be a field and during transit or storage, causing seedling potential plant pathogen to local vascular plants, damping off, cottony leak and rotting of the root, based on artificial inoculation (Bridge et al. 2008). stem, fruit, and vegetable heads (Yu 1940; Yu et al. Other species caused diseases in fish (Khulbe 2009), 1945). He also conducted pioneering studies on the marine red algae (Takahashi et al. 1977) and physiology of this important pathogen and mammals including humans (de Cock et al. 1987; recommended measures to control the disease (Yu Mendoza et al. 1996; Thianprasit et al. 1996). On 1934; Yu et al. 1945). In addition, he reported two the other hand, Pythium spp. may be of potential species of Pythium in Yunnan Province: P. benefits to human beings as biological control agents spinsosum Sawada and P. ultimum Trow which were of soil-borne fungal pathogens (Jones 1995) and weakly pathogenic to the roots of broad beans (Yu mosquitoes (Su 2006; Su et al. 2001), as well as a 1950) and P. spinosum caused black rot of yam bean source of chemicals useful in medicine and food (Yu 1955). Finally he described 8 species of Pythium industry (Gandhi & Weete 1991; Stredansky et al. attacking the seedlings of millet, with varying 2000). degree of virulence: P. aristosporum Vanter., P.

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arrhenomonas Drechsler, P. debaryanum R. Hesse, commonly recovered from moist, fertile, cultivated P. graminicola Subraman., P. irregulare Buisman, P. vegetable garden soil, especially in the spring. Ma & monospermum Pringsh., P. tardicrescens Vanterp. Yu (1988) reported 8 aquatic species of Pythium: P. and P. ultimum (Yu 1978). aquatile Hӧnk, P. dissotocum Drechsler, P. However, a new era of the study of Pythium in intermedium de Bary, P. middletonii Sparrow, P. mainland China began when Professor Y.N. Yu periplocum Drechsler, P. rostratum and P. torulosum became interested in the genus. While he was still at Coker & P. Patt. Pythium aquatile was a new record Sichuan University he and his colleagues already in China whereas P. myriotylum Drechsler was the reported the root rot disease of pyrethrum caused by first isolation from water in the world. All species Pythium sp. (Ho et al. 1951). After he joined the were isolated for the first time in China except P. Institute of Microbiology, Chinese Academy of middletonii which had been isolated as P. proliferum Sciences in Beijing he launched an outstanding Schenk. (=P. middletonii) from termite larvae in research program on the taxonomy and occurrence water in Yunnan Province (Shen & Siang 1948). of Pythium species in China that lasted for over two Finally, based on their extensive experience with decades. Thus, he described 5 new species isolated Pythium species he and his student G.Z. Ma put from soil in mainland China: P. acrogynum Y. N . Yu, together a comprehensive monograph on the genus P. amasculinum Y. N . Yu , P. connatum Y.N . Yu, P. Pythium in China (Yu & Ma 1989) including not kummingense Y. N . Yu an d P. s in e n s i s Y. N . Yu ( Yu only an identification key and detailed descriptions 1973) and described several methods for the on 54 species of Pythium recorded from China but isolation of Pythium species from soil (Yu 1975). In also useful information on the materials and 1986 he discussed the taxonomic position of methods, morphology, physiology, ecology and Pythium in the systematics and taxonomy of the taxonomy of the genus as well as a list of helpful oomycetes (Yu 1986). He and his students conducted references. It proved to be a milestone in the study a taxonomic study on the Pythium species from of the genus in China and even after over 20 years Yunnan Province (Yu et al. 1987). Of the 19 species since its publication, the monograph is still widely collected in the province 5 were new records (P. used as the standard reference for studies on helicoides Drechsler, P. nagaii S. Ito & Tokun., P. Pythium species in China. Nevertheless, as a periilum Drechsler, P. ro s tratu m E.J. Butler and P. dedicated scientist, Professor Yu did not rest on his vexans) and one new species: P. hypoandrum Y.N . laurels. Subsequently, he and his students (Ma et al. Yu & Y.L. Wang was described. In his discussion on 1990) studied the genus Pythium in Ningxia and the ecology and distribution of the genus Pythium in found 10 species new to that region: P. China (Yu 1987) he presented 45 species from aphanidermatum, P. catenulatum V. D . M a t h e w s, P. various kinds of soil and infected plant tissues irregulare, P. oligandrum Drechsler, P. throughout the country and found that P. pulchrum paroecandrum Drechsler, P. periplocum Drechsler, Minden and P. aphanidermatum to be the most P. perplexum H. Kouyeas & Theoh. (a new record widely distributed species in Chinese soil, followed for China), P. salpingophorum Drechsler, P. ultimum by P. spinosum, P. s in e ns is and P. carolinianum V. D . and P. vexans. Yu and Ma continued to explore other Mathews and most species of Pythium were new methods that can be used in the species

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differentiation of Pythium. They found that growth numerous researchers also conducted study of responses to temperatures (especially the maximum Pythium species in various parts of China. Many temperatures) were useful in the speciation of the species of Pythium were pathogenic to cereal plants genus and can supplement the species identification and turfgrass from the Family Gramineae (Poaceae) based on morphology (Yu & Ma 1990). All Pythium as well as herbaceous plants, especially fruits and species in China could be segregated into 4 distinct vegetables from Family Crucifereae (Brassicaceae), groups based on the maximum temperatures for Family Solanaceae and Family Cucurbitaceae. They growth: 32℃, 36℃, 40℃ and 44℃. Grouping of were commonly found in soil either as saprophytes species did not seem to have systematic significance or as soil-borne pathogens. In addition to P. but helped with identification. So P. amasculinum, spinosum that caused seedling damping off of millet treated temporarily by Plaats-Niterink (1981) as as reported by Yu (1950), Xu & Zhang (1985) conspecific with P. oligandrum, was found to be reported that P. aphanidermatum was strongly different not only morphologically but in the pathogenic to maize in Shandgong Province maximum growth temperatures: 40℃ for P. resulting in root and basal stalk rot. However, the amasculinum and 44℃ for P. oligandrum, maize stalk rot in Jiangsu Province (Zhu et al. 1997) confirming that they were two distinct species. Ma was attributed to P. inflatum V.D. Mathews (first & Yu (1991) further demonstrated the value of record from maize) and P. graminicola. Wu et al. electrophoresis of soluble proteins on disc (1990) also confirmed that the causal pathogen of polyacrylamide gel disc in the taxonomy of Pythium stalk rot of maize in China was P. graminicola. Shen species. The results clearly indicated that the protein & Zhang (1994) identified the pathogenic species patterns of conspecific isolates were similar whereas from wheat and barley in Zhejiang Province as P. those of isolates from different species were quite dissotocum, P. irregulare, P. polypapillatum T. Ito diverse. The comparison between the protein (new record in China), P. spinosum and P. ultimum. banding patterns of P. kunmingense and P. irregulare Eight species of Pythium were isolated from spring proved that these two morphologically similar cropping maize seedlings in Zhejiang Province: P. species were different taxa. Therefore, the acanthophoron Sideris, P. aphanidermatum, P. taxonomic criteria in the identification of Pythium debaryanum, P. gramincola, P. irregulare, P. species in China were re-evaluated (Yu et al. 1990). spinosum, P. ta rd ic re s c en s and P. ultimum with P. Professor Yu capped his distinguished research aphanidermatum as the most virulent pathogen career on Pythium in China by updating the list of (Shen & Zhang 1995). In a study of maize wilt in Chinese Pythium species and providing description Guangxi, Guangdong and Hunan provinces, Zhang for each species, as part of the comprehensive record (1997) demonstrated that the disease was caused of the fungal flora in China (Yu 1998) and the primarily by P. salinum Hӧhnk, P. orthogonon conduction, by invitation, of a workshop on Pythium Ahrens and P. spinosum. Various Pythium spp. were identification at the National Institute of Agricultural responsible for the yellowing and blight of rice Science and Technology in The Republic of Korea in seedlings on dry seedbed: P. aphanidermatum and P. July 2000 (Yu 2003). catenulatum in Jiangsu Province (Xu et al. 2001) Besides Professor Y.N. Yu and his students, and P. salinum, P. intermedium as well as P.

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acrogynum in Nanjing area (Gao et al. 2001). Lou & grass diseases in summer of Beijing were caused by Zhang (2004) identified P. sylvaticum W.A. Pythium spp. which attacked primarily F. Campbell & F.F. Hendrix from damping-off arundinacea whereas Gu et al. (2009) determined seedlings of rice` in Hangzhou region, a new record that the pathogen of root rot of turf grass in the City of this species in China. Wang et al. (1996) isolated of Lanzhou to be P. aphanidermatum. 10 species of Pythium from the rhizospheres of Miscellaneous species of Pythium were also wheat in Zhejiang Province: P. adhaerens Sparrow, reported by other researchers from soil and plant P. aphanidermatum, P. arrhenomanes, P. materials. Duan (1985) isolated from soil in Beijing catenulatum, P. diclinum Tokun., P. dissotocum, P. a new species: P. bo rea le R.L. Duan and three newly irregulare, P. pulchrum, P. spinosum and P. ultimum reported species from soil and diseased cucumber with P. adhaerens, P. catenulatum and P. pulchrum seedlings: P. oligandrum, P. m y r io ty lum and a as new records for the province. All ten Pythium variant of P. ultimum. Jiang et al. (1990) isolated 18 species were pathogenic to wheat, rice, tomato and species of Pythium from Shangdong, Jiangsu, Anhui, aubergine but P. irregulare and P. spinsoum were the Jiangxi and Fujian provinces as well as Shanghai most virulent species, respectively, to wheat and region. The dominant pathogenic species were P. rice. ultimum, P. aphanidermatum, P. irregulare and P. Turf grass of parks, golf courses and lawns was spinosum whereas P. acanthicum Drechsler, P. susceptible to various diseases. Wang et al. (2000, acanthophoron, P. kunmingense and P. mamillatum 2001) identified 6 species of Pythium causing were new records for east China. Zhang & Jiang damping off as well as rotting of stems and leaves of (1990) identified P. aphanidermatum, P. dissotocum, 4 common cool-season grass species (Festuca P. kunmingense, P. s p ino sum and P. ultimum which arundinacea, Poa pratensis, Agrostis palstriss and were pathogenic to vegetable seedlings in Yinchuan, Lolium perenne) in Zhejiang Province: P. Yongning, Wuzhong, Linwu and Qingtonlin. Zhang aphanidermatum, P. deliense, P. irregulare, P. et al. (1990) further proved that the damping-off of ultimum, P. graminicola and P. mamillatum Meurs. solanaceous and cucurbitaceous vegetables caused and studied the conditions affecting Pythium by P. spinosum, P. aphanidermatum, P. irregulare infection. Pythium spp. were also implicated in and P. ultimum in the field was affected by soil causing diseases of cool-season lawns and turf in temperature, moisture and rainfall. Pythium Shanghai region (Ma et al. 1999) as well as Weifen spinosum was abundant during the winter and spring area of Shandgong Province (Ding & Ma 2005). Liu while P. aphanidermatum peaked in the summer. & Xie (2003) studied the main diseases of cold Chinese cabbages throughout Guangdong Province season turf grass in the Hexi Corridor in Gansu suffered a serious soft rot disease caused by P. Province and found that Poa pratensis and L. aphanidermatum and its pathogenicity to 18 species perenne could be infected, respectively, by P. of plants belonging to 7 families was confirmed (Liu aphanidermatum and Pythium sp. whereas Xue 1998). A survey of diseases of watermelons in (2003) determined that P. graminicola was Lianing, Jilin, Heilongjiang, Hebei, Henan and pathogenic to these two species of grass and F. Shangdong provinces revealed that the fruit rot was rubra. Chai & He (2002) showed that the main turf caused by P. aphanidermatum and P. debaryanum

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(Wei et al. 1991). Whereas the stem rot of lotus lily due to P. aphanidermatum, P. monospermum and P. in Nanjing of Jiangsu Province was caused by P. acanthicum (Zhao et al. 2009). The pathogens helicoides (Dou et al. 2010). P. elongatum was the causing the mungbean sprout spoilage, root rot of causal agent in Hanzhong region of Shaanxi kidney bean and seedling rot of Calathea sp. were Province. From a total of 226 tobacco plants identified, respectively, as P. aphanidermatum showing root neck rot symptoms and 60 soil samples (Zhang et al. 2010b), P. ultimum (Wang et al. 2010b) collected from 11 tobacco planting areas in Yunnan and P. myriotylum (Oishi et al. 2010). Province, 4 species of Pythium were isolated: P. Whereas most species of Pythium attacked aphanidermatum, P. debaryanum, P. ultimum and P. seedlings and the succulent tissues of vegetables, irregulare and their pathogenicity to tobacco was fruits, roots, stems and leaves of herbaceous plants, established, resulting not only in root neck rot but some species are pathogenic to woody plants as seedling blight as well and the most harmful well. Qiu et al. (1986) found that P. ultimum caused pathogen was P. aphanidermatum (Wang 1997) root rot of young Chinese fir trees in Sichuan which was also isolated from tobacco field (Chen et Province leading to the yellowing of leaves and al. 2009). Pythium myriotylum caused serious subsequent death after three to four years. rhizome rot of ginger in Laiwan City of Shangdong Rhododendron foot rot was a severe disease in Province (Liu & Shi 2009). From 1998 to 2001, Yixing, Jiangsu Province, leading to the wilting of Yuan & Lai (2003) conducted a comprehensive seedlings and mature plants, often resulting in death study of the genus Pythium in Nanning, Guangxi of the entire plants. The causal pathogen proved to Zhuang Autonomous Region, by isolating Pythium be P. kunmingense (Chen et al. 1997). Based on species from 106 soil samples collected from samples collected in 15 citrus-producing cultivated land of 11 counties and reported two new counties/cities in Sichuan, P. debaryanum, P. species of Pythium: P. faciforme G.Q. Yuan & C.Y. hydnosporum (Mont.) Schrӧt and P. hemmianum M. Lai and P. nanningensis C.Y. Lai & G.Q. Yuan and 6 Takah. were identified causing root rot of citrus trees Pythium species new to Guangxi area: P. (Zhang & Huang 1994). In Hanzhou and Sichuan acanthophoron, P. kunmingense, P. irregulare, P. Province, cultivated tea plants were often started middletonii, P. tardicrescens and P. ultimum with P. with stem cuttings but the roots developed from the aphanidermatum and P. spinosum as the dominant cuttings could be rotted by P. spinosum (Lai et al. species (Yuan & Lai 2004). Fu et al. (2005) also 1998, 2000). Poinsettia was susceptible to P. studied the distribution of Pythium species in the aphanidermatum which induced root rot disease in northern part of Guangxi Province and recovered 15 Shanghai’s Pudong New Area (Yang et al. 2003). species of Pythium with 7 species as new records in Pythium aphanidermatum was identified as one of the area: P. acanthicum, P. aquatile, P. dissotocum, the two pathogens causing stem base rot of papaya P. elongatum, P. amasculinum, P. graminicola and P. (Li et al. 2007) whereas P. oligandrum was the pulchrum whereas P. aphanidermatum was the pathogen causing canker disease of walnut (Shang et dominant species, followed by P. deliense and P. al. 2010). spinosum. The processing tomato, an important crop With the advent of molecular biology, Fu et al. in Xinjiang Province, often suffered root rot diseases (2004) pointed out the importance of using

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molecular data, like the nucleotide sequence of the breve Y.Y. Long, J.G. Wai & L.D. Guo from rDNA internal transcribed spacer (ITS) region as an grassland (Long et al. 2011). Lou et al. (2000) used important taxonomic tool to supplement the 25 random primers to conduct a Random Amplified traditional morphological studies. Their view was Polymorphic DNA (RAPD) analysis of 8 species of echoed by Zhang & Su (2005), Chen et al. (2007), Pythium causing tomato seedling damping off Zhang & Li (2008) and Chai et al. (2009). Thus, disease in Hanzhou region and demonstrated the based on morphological features and the comparison nearest genetic relationship between P. kunmingense of nucleotide sequence of the ITS region of rDNA and P. irregulare, between P. aphanidernatum and P. with the data in GenBank, 10 species of Pythium tardicrescens and between P. ultimum and P. from various vegetables and fruits in Zhejiang debaryanum. Furthermore, these species could be Province were identified (Lou & Zhang 2005), while classified into three groups, with P. kunmingense, P. the identity of P. carolinianum in Gansu Province spinosum and P. irregulare forming the first group, (Li & Chai 2010), P. oligandrum from walnut P. aphanidermatum and P. tardicrescens the second (Shang et al. 2010), P. helicoides from Victoria group and P. ultimum, P. dissotocum as well as P. ‘Longwood hybrid’ (Dou et al. 2010) and P. vexans debaryanum the third group. from Dendrobium (Tao et al. 2011) was confirmed. Although Pythium species are well known as The following Pythium species were similarly plant pathogens they can attack other organisms as identified from primarily rhizosphere soils: P. well. The red alga, Porphyra yezeonens widely ultimum and P. scleroteichum Drechsler (a new cultivated along the sea coasts of northern provinces record in China) from corn in Honggu and Quilhe including Shangdong, Zhejiang and Jiangsu was districts of Lanzhou; P. heterothallicum W.A. infected by P. porphyrae M. Takah. & M. Sasaki Campb. & F.F. Hendrix (a new record in China) causing red rot (Ma 1996; Ding & Ma 2005; Ding from bean, grape, cabbage and corn in Lanzhou and 2006) resulting in considerable losses. The isolation Zhangye of Gansu Province (Gan et al. 2010); P. of a new strain of P. carolinianum from the infected nunn Lifsh., Strangh. & R.E.D. Baker, for the first larvae of Culex albopictus and C. quinquefasciatus time in China, from nurseries in Beijing (Cheng et in Guiyang City of Guizhou Province in 1995 (Su et al. 2012); P. carolinianum from kidney bean, for the al. 2001) was an important discovery due to its first time, in Gansu Province (Li & Chai 2010). The potentials in controlling mosquito population and identification of Pythium species like P. many follow-up studies were conducted. Huang & carolinianum based on rDNa-ITS sequence analysis Su (2001) studied the cytology of infection of is especially important because it produces only mosquito larvae by the hyphae and zoospores by sporangia but no sexual structures, making precise means of fluorescence and scanning microscopes identification by morphological characters alone and the cDNA library was successfully constructed difficult. In addition, 3 new species of Pythium have (Liu et al. 2001). It was also demonstrated that P. thus been identified in Nanning of Guangxi carolianianum produced Pr1- and Pr-2 like protease Province: P. guangxiense Y.Y. Long & J.G. Wai from in response to the chitin of mosquito cuticle (Su vegetable fields (Long et al. 2010) as well as P. 2002). A cDNA fragment of Pr1 gene was isolated baisense Y.Y. Long, J.G. Wai & L.D. Guo and P. and cloned (Su 2003; Shi & Su 2003). Huang & Su

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(2003) also studied the effects of environmental pesticides on the fungus and the mosquito, C. factors on the sporulation of the fungus because the quinquefaciatus in Guizou Province was also zoospores were probably the primary infective studied (Zhang & Su 2008a). inocula of mosquito larvae. In addition, the mosquito The species of Pythium found so far in host range of P. carolinianum was determined (Su et mainland China are presented in Table 1 and the al. 2003). Yang et al. (2005a, b) constructed a mini hosts for the pathogenic species are listed in Table 2. genomic DNA library as an efficient and Additional information was obtained from Sylloge expeditious strategy to search for unknown Fungorum Sinicorum (Tai 1979), Atlas of Insect sequence adjacent to the known so as to obtain the Pests and Diseases of Vegetable Crops in China (Lu full-long genomic sequence of the subtilisin-like et al. 1992), Fungal Diseases of Cultivated protease (Pr1) gene. In 2006 a new species of Medicinal Plants in Guangdong Province (Qi 1994), Pythium was isolated from diseased larvae of Aedes Plant Pathology Volume of China Agriculture albopictus in Guiyang of Guizhou Province: P. Encyclopedia (Editorial Council 1996), and Sylloge guiyangense X.Q. Su and its identity was Fungorum Sinicorum Vol. 6 (Yu 1998). The Pythium confirmed by the ITS sequence of rDNA (Su 2006). spp. found in Taiwan (Ho 2009, 2011) and Hainan Huang & Su (2007) conducted further studies on Island (Ho 2012) are also included in Table 1 for the in vitro growth requirements of the fungus. In comparision. order to ensure safety to the ecosystem should the 1.2 Plant disease control fungus be applied on a large scale to control In order to control the numerous plant diseases mosquito population in the field, various studies caused by Pythium species in mainland China it was were conducted to demonstrate its safety to animals essential to have an understanding of the physiology ( Liu & Su 2007a, b), other insect larvae ( Liu et al. and pathogenesis of the pathogens. The nutritional 2007a) and cultivated plants (Zhang & Su 2008a, and temperature requirements were often studied b). A list of its mosquito hosts was compiled (Su along with the report of the pathogens. Chen & Lin 2008). Scanning electron microcrospy was used to (1949) studied the inhibition of the growth of P. study the hyphae and asexual structures (Kong et aphanidermatum by anions while Chen et al. (1989) al. 2008) and its genetic library was constructed investigated the factors inducing the zoospore (Hong & Su 2008). The subtilisin-like protease production of P. d e l ie n s e . In addition, Ji et al. (Pr1) was identified, purified and characterized (2000) conducted a detailed study on the (Wang et al. 2007a; Yu et al. 2007; Duan et al. ultrastructural resistance to stalk rot in maize caused 2008) whereas the induction conditions for Pr2 by P. inflatum and Yang et al. (2001) determined that were elucidated (Yu et al. 2008b). The protoplast of the resistance to the pathogen was controlled by one P. guiyangense was successfully recovered and dominant gene in the host. In the study of the regenerated (Zhao et al. 2008) providing the pathogenesis of P. aphanidermatum He et al. material to allow for genetic transformation (1992a) showed that the zoospores aggregated at the mediated by Agrobacterium tumefaciens (Zhao & region of root hairs and root caps of tomato and Su 2008) in order to produce more virulent begonia and penetrated the cell walls directly by mosquito-killing strains. The effect of five common germ tubes, Chen et al. (1996) demonstrated that the

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Table 1 Presence of Pythium species in mainland China, Taiwan and Hainan Island

Species Mainland China Taiwan Hainan acanthicum Drechsler + + + acanthophoron Sideris + – + acrogynum Y.N. Yu (1973)* + – – adhaerens Sparrow + + – afertile Kanouse & T. Humphrey – + – amasculinum Y.N. Yu (1973)* + – – aphanidermatum (Edson) Fitz. + + + aquatile Hӧhnk + – – aristosporum Vanter. + + + arrhenomanes Drechsler + + + baisense Y.Y. Long, J.G. Wai & L.D. Guo (2012)* + – – boreale R.L. Duan (1985)* + – – breve Y.Y. Long, J.G. Wai & L.D. Guo (2012)* + – – carolinianum V.D. Mathews + + + catenulatum V.D. Mathews + + + chamaehyphon Sideris + – – coloratum Vaartja + + – connatum Y.N. Yu (1973)* + – – cucurbitacearum S. Takim. – – + debaryanum R. Hesse – + – deliense Meurs + + + diclinum Tokun. + – – dimorphum F.F. Hendrix & W.A. Campbell – + – dissotocum Drechsler + + + echinocarpum S. Ito & Tokun. + – – elongatum V.D. Mathews + + – falciforme G.Q. Yuan & C.Y. Lai (2003)* + – – gracile Shenk – + – gramincola Subraman. + + + guiyangense C.Q. Su (2006)* + – – guangxiense Y.Y. Long & J.G. Wai (2010)* + – – helicandrum Drechsler – + – helicoides Drechsler + + + hemmianum M. Takah. + – – heterothallicum W.A. Campb. & F.F. Hendrix + – – hydnosporum (Mont.) Schröt. – + + hypoandrum Y.N. Yu & Y.L. Wang (1987)* + – – indigoferae E.J. Butler + – + inflatum V.D. Mathews + + +

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Table 1 continued intermedium de Bary + + + irregulare Buisman + + + kunmingense Y.N. Yu (1973)* + – – mamillatum Meurs + + – marsipium Drechsler + + + middletonii Sparrow + + + monospermum Pringsh. + + + myriotylum Drechsler + + + nagaii S. Ito & Tokun. + – – nanningense C.Y. Lai & G.Q. Yuan (2003)* + – – nunn Lifsh., Strangh. & R.E.D. Baker + – – oedochilum Drechsler – + + orthogonon Ahrens + – – oligandrum Drechsler + + – palpingenes Drechsler – + – paroecandrum Drechsler + + + periilum Drechsler + + + periplocum Drechsler + + – perplexum H. Kouyeas & Theoh. + + – pleroticum Drechsler – + – polymastum Drechsler – + – polypapillatum T. Ito + – – porphyrae M. Takah. & M. Sasaki + – – pulchrum Minden + + + rostratum E.J. Butler + + – salinum Höhnk + – – salpingophorum Drechsler + + – scleroteichum Drechsler + – – sinensis Y.N. Yu (1973)* + – – spinosum Sawada + + + splendens Han Braun + + + sukuiense W.H.Ko, S.Y. Wang & P.J. Ann (2004)** – + – sylvaticum W.A. Campbell & F.F. Hendrix + + + tardicrescens Vanterp. + + – torulosum Coker & P. Patt. + + – ultimum Trow + + + undulatum H.E. Peterson – + – vexans de Bary + + + volutum Vanterp. & Truscott – + – Note: * New Pythium species found in mainland China; ** New Pythium species found in Taiwan.

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Table 2 Pathogenic species of Pythium in mainland China

Parasitic spp. on plants Hosts acanthicum Cucumis sativus, Lycopersicum esculentum, Zea mays acanthophoron Zea mays acrogynum Oryza sativa adhaerens Lycopersicum esculentum, Oryza sativa, Solanum melongena, Triticum aestivum Agrostis palstriss, A. stolonifera, Aleuritis fordii, Amaranthus tricola, Benincasa hispida, Begonia chinensis, Begonia spp., Beta vulgaris, Brassica chinensis, B. oleracea var. capitata, B. pekinensis, B. napus, Brassica spp., Capsicum annuum (frutescens), C. frutescens var. grossum, Carica papaya, Citrillus vulgaris, Chrysanthemum cineriaefolium, Chrysanthemum spp., Cucumis melo., C. melo var. hami, C. sativus, Cucurbita maxima, Cu. moschata, Cu. moschata var. meloniformis, Cu. pepo, Daucus carota var. sativa, Diospyros kaki, Euphorbia pulcherrina, Festuca arundinacea, aphanidermatum Gossypium herbaceum, G. hirsutum, Gossypium spp., Ipomaea batatas, I. reptans, Lagenaria siceraria, L. siceraria var. clavata, Lolium perenne, Luffa acutangula, L. cylindrical, L. leucantha, Lupinus spp., Lycopsersicum esculentum, Malva sylvestris, Momordica charantia, Nicotiana tabacum, Oryza sativa, Pachyrhizus tuberosus, Phaseolus vulgaris, Poa pratensis, Raphanus sativus, Secale cereale, Setaria italica, Solanum melongena, Sorghum vulgaris, Spinacia oleracea, Triticum aestivum, Zea mays aristosporum Setaria glauca, Setaria italica, Setaria viridis Capsicum annuum (frutescens), Chrysanthemum spp., Cucumis sativus, Lycopersicum esculentum, Orya sativa, arrhenomanes Saccharum officinarum, Setaria italica, Solanum melongena, Sorghum vulgaris, Triticum aestivum, Zea mays Daucus carota, D. carota var. sativa, Lycopersica esculatum, Oryza sativa, Solanum melongena, Triticum aestivum, catenulatum Vigna sinensis Brassica oleracea var. capitata, Citrus spp., Cucumis melo, C. sativus, Gossypium hirsutum, Lycopersicum debaryanum esculentum, Panax schinseng, Pinus massoniana, Solanum melongena, Nicotiana tabacum, Setaria italica, Sorghum vulgaris, Zea mays Agrostis palstriss, A. stolonifer, Brassica spp., Capsicum annuum (frutescens), Cucumis melo, C. sativus, Festuca deliense arundinacea, Lolium perenne L., Lycopersicum esculentum, Poa pratensis, Solanum melongena Capsicum annuum (frutescens), C. sativus, Chrysanthemum spp., Lycopersicum esculentum, Oryza sativa, Solanum diclinum melongena, Triticum sativum Capsicum annuum (frutescens), Chrysanthemum spp., Cucumis sativus, Hordeum vulgare, Glycine max, Lycopersicum dissotocum (=oryzeae) esculentum, Solanum melongena, Triticum aestivum, Vicia faba, Oryza sativa echinocarpum Oryza sativa elongatum Nelumbo nucifera Agrostis palstriss, A. stolonifera, Capsicum annuum (frutenscens), Festuca arundinacea, Hordeum vulgare, Lolium graminicola perenne, Poa pratensis, Setaria italica, S. magna, Soghum vulgare, Triticum aestivum, Vicia faba, Zea mays, Zingiber officinale helicoides Victoria (‘Longwood hybrid’) hemmianum Citrus spp. heterothallicum Zea mays hydnosporum Citrus spp. kunmingense Lycopersicum esculentum, Rhododendron spp. orthogonon Zea mays inflatum Oryza sativa intermedium Oryza sativa, Pachyrrhizus erosus, Phaseolus vulgaris, Pisum sativum Agrostis palstriss, A. stolonifera, Capsicum annuum (frutenscens), Chrysanthemum spp., Cucumis sativus., Festuca arundinaceae, Hordeum vulgare, Lactuca sativa, Lagenaria siceraria, Lolium perenne, Lycopersicum esculatum, irregulare Nicotiana tobacum, Oryza sativa, Pachyrhizus erosus, Poa pratensis, Setoria italica, Solanum melongena, Sorghum vulgaris, Spinacia oleracea, Triticum aestivum, Vicia faba, Zea mays, Zingiber italica

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Table 2 continued mamillatum Agrostis palstriss, A. stolonifera, Festuca arundinacea, Lolium perenne, Poa pratensis Capsicum annuum (frutenscens), Chrysanthemum spp., Cucumis sativus, Lycopersicum esculentum, Solanum middletonii melongena monospermum Lycopersicum esculentum, Setaria italica, Zingiber officinale myriotylum Calathea sp., Cucumis sativa, Glycine max, Inula japonica, Lycopersicum esculentum, Zingiber officinale Brassica pekinensis, Capsicum annuum (frutescens), Chrysanthemum spp., Cucumis sativus, Family Crucifereae, oligandrum Juglans nigra, Lycopersicum esculentum, Solanum melongena orthogonon Zea mays Allium cepa, A. cepa var. aggregatum, A. fistulosum, A. graveolens, A. sativum, A. tuberosum, Apium graveolens, paroecandrum Brassica pekinensis, Family Crucifereae periplocum Allium sepa, A. cepa var. aggregatum, A. porrum, A. sativum, A. tuberosum perplexum Allium tuberosum polypapillatum Hordeum vulgare, Triticum aestivum pulchrum Lycopersicum esculentum, Oryza sativa, Solanum melongena, Triticum aestivum rostratum Oryza sativa, Vicia faba salinum Oryza sativa, Zea mays sinensis Capsicum annum (frutescens), Lycopersicum esculentum Chrysanthemum spp., Capsicum sp., Cucumis sativus, Glycine max, Hordeum vulgare, Lycopersicum esculentum, spinosum Oryza sativa, Pachyrhizus tubersosus, Solanum melongena, Thea sinensis, Triticum aesticum, Vicia faba, Zea mays sylvaticum Glycine max, Gossypium, Oryza sativa tardicrescens Lycopersicum esculentum, Setaria italica, Zea mays Capsicum annuum (frutenscens), Chrysanthemum spp., Cucumis sativus, Lycopersicum esculentum, Solanum torulosum melongenae Agrostis palstriss, A. stolonifera, Amomum compactum, Am. krarvanh, Allium cepa, A. cepa var. aggregatum, A. fistulosum, A. porrum, A. sativum, A. tuberosum, Brassica campestris, B. juncea var. cripifolia, B. pekinensis, Calotropis procera, Capsicum annuum (frutescens), Carica papaya, Chrysanthemum spp., Cucumis sativus, Cunnuinghamia lanceolata, Daucus carota var. sativa, Festuca arundinacea, Family Crucifereae, Fragaria ananassa, ultimum Hordeum vulgare, Leucaena leucocepha, Lolium perenne, Lycopersicum esculentum, Oryza sativa, Nicotiana tabacum, Pachyrhizus bulbosus, P. erosus, Papaver rhoeas, Phaseolus vulgaris, Pisum sativum, Poa pratensis, Portulaca pilosa, Raphanus sativa, Scutellaria baicalensis, Setaria italica, Solanum melongena, Sorghum vulgaris, Triticum aestivum, Vicia faba, Vigna unquiculata, Zea mays Dendrobium aurantiacum, D. chrysanthum, D. chrysotoxum, D. thyrsiflorum, Dioscorea opposita, Setaria italica, vexans Solanum tubersoum, Sorghum vulgaris, Zea mays Agrostis spp., Amaranthus tricolor, Ananas sativus , Antirrhinum major, Calendula officinalis, Celosia argentea var. cristata, Chrysanthemum cineriaefolium, Citrus spp., Family Araceae, Family Cucurbitaceae, Festuca arundinacea, unidentified species Impatiens balsamina, Lolium perenne, Manihot esculenta, Nelumbo nucifera, Nicotiana tabacum, Pachyptera alliaceae, Pelargonium hortorum, Poa pratensis, Solanum melongena, Spinacia oleraceae, Vicia faba Parasitic on algae porphyrae Porphyra yezoensis Parasitic on mosquito

larvae Aedes albopictus, A. elsiae, A. formosensis, A. novoniveus, Anopheles sinensis, Culex mimulus, C. minor, C. carolinianum pseudovishnui, C. pipens quinquefasciatus, C. theileri, C. tianpinggensis, C. tritaeniorhynchus Aedes albopictus, A. eagypti, A. elsiae, A. formosensis, A. novoniveus, Anopheles sinensis, Culex mimulus, C. minor, C. guiyangense pipiens pallens, C. pseudovishnui, C. pipiens quinquefasciatus, C. theileri, C. tianpinggensis, C. tritaeniorhynchus

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pathogen induced cucumber seedling damping-off effect and proved to be highly toxic to the mycelial by the production of polygalacturonase and other growth of P. aphanidermatum in vitro (Zhu et al. cell wall-degrading enzymes and Xu et al. (2009a) 2010) and seed coating with a mixture of these two discovered the destruction of chlorophyll, β-carotene fungicides proved to be effective in controlling and other cellular changes in Lolium perenne due to Pythium diseases of Poa pratensis (Wang 2010). the infection by P. aphanidermatum. Azoxystrobin, metalaxyl, maxim and difenoconazole Various measures have been developed to showed strong toxicity against P. graminicola and control plant diseases caused by Pythium species. treating the seeds with these chemicals had control For pragmatic reasons, chemicals were commonly effect on corn stalk rot (Zhang et al. 2010d). used because of they were fast acting, effective and Isothiocyanate could be used to disinfect the soil in easy to handle. In his pioneering study on Pythium the greenhouse using drip irrigation system in order diseases, Yu (1934) suggested the use of acetic acid to control Pythium species (Xiao et al. 2010). Under in the soil could eliminate completely the damping laboratory conditions, other chemicals were tested off of cucumber seedlings and caused no injuries to for their fungicidal potentials. For instance, the the seeds and seedlings. The toxicity to the pathogen growth of P. aphanidermatum was strongly inhibited was probably due to the acetate anions (Chen & Lin by propamocarb (Liu et al. 2007b) and 1949). Zheng (1997) found that zinc sulfate difenoconazole (Jiang et al. 2004). Hymexazol, inhibited the growth of P. salimum, P. orthogonon pyraclostrobin, metiram and bonopol proved to be and P. sp ino sum , the causal agents of basal stalk rot toxic to P. myriotylum that caused ginger rhizome rot of maize in Guangxi Province and it could be used (Yuan et al . 2011). Various fungicides were tested to control the disease in the field effectively. Later against Pythium sp. causing garlic rot and the on, more potent fungicides were found to be mycelial growth in vitro was inhibited by inhibitory to Pythium species and thus utilized to thiophanate-methyl, copper sulphate, mancozeb, control the diseases caused by them. For instance, copper hydroxide, cymoxanil, mancobez, metiram, Pythium blight of turf grass could be controlled by famoxas and cymoxanil (Zhang et al. 2008). the applications of thiophanate-methyl, mancozeb However, some isolates of Pythium developed and chlorothalonil (Han & Mu 2000). Gao et al. resistance to fungicides, especially to the widely (2001) showed that seed treatment combined with popular metalaxyl and biological control using soil treatment by hymexazol, metalaxyl or antagonistic bacteria, like Pseudomonas spp. proved diisothiocyanatomethant was very effective in the to be a viable alternative (Zhang et al. 1990a; Lou et control of rice blight caused by P. s a lin um , P. al. 2001, 2002). From the rhizosphere soil of healthy intermedium and P. acrogenum. Hymexazol and tobacco plants in a heavily diseased field in Yunnan, metalaxyl were also used in the control of poinsettia 16 strains of Rhizobacteria were obtained with root rot (Yang et al. 2003). The P. aphanidermatum- inhibiting effect on damping off Pythium spp., induced root rot of melon seedlings in Gansu comparable to that of metalaxyl and 6 strains even Province was effectively controlled by coating them showed promoting effect on the tobacco seedlings with Vitavax FF (Wang 2004). A combination of (Fang 2001). Based on pot and field experiments in metalaxyl and hymexazol seemed to have synergistic Zhejiang Province, the biological control efficiency

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of Pseudomonas aeruginosa against the metalaxyl-mancozeb (Chen et al. 2009). Chen et al. metalaxyl-resistant P. ultimum and P. spinosum was (2004, 2005) demonstrated that T. harzianum 94.4 and 51.4% respectively. In Shangdong controlled seedling damping off and root rots caused Province, P. aphanidermatum caused the by P. ultimum by stimulating the production of plant damping-off of cucumber seedlings and the control proteomics, thus accounting for the induced efficacy of Paenibacillus polymyxa was tested in resistance in the host plants. Although P. oligandrum vitro and in vivo (Pan et al. 2008). The bacterium could be plant pathogenic it is also a mycoparasite. lysed the hyphal wall resulting in the leakage of In vitro studies proved that it was antagonistic protoplast and the failure to form oospores. The against other plant pathogenic species of Pythium: P. disease control efficiency was similar to that of the ultimum, P. spinosum and P. irregulare (He et al. fungicide propamocarb. Moreover, it did not affect 1992b). Treating tomato with oospores of P. the germination rate of cucumber seed but actually oligandrum resulted in effective reduction of 79.4% could increase the emergency rate and improve the and 63.6% of seed rot and damping-off induced by seedling growth. From the rhizosphere of ginger, P. ultimum due to substances produced to dissolve Pseudomonas fluorescens and Alcaligenes faecalis the hyphae of the latter. Gu et al. (2011) were also isolated and proved to be antagonistic demonstrated that T. aureoviride inhibited in vitro against P. myriotylum which caused the ginger growth of P. aphanidermatum, the causal agent of rhizome rot (Wang et al. 2010a). Bacillus turfgrass root rot, with the same efficiency as the megaterium could induce systemic resistance in fungicide, metalaxyl and the inhibibition was cucumber against seedling damping-off by attributed to the penetration and parasitizing the stimulating several plant defense-related enzymes in hyphae of the pathogen. In addition, an elicitin-like the host plant (Liang et al. 2011). protein (oligandrin) produced by P. oligandrum Mycoparasitic fungi could also be used to could induce systemic resistance in the host plants control Pythium diseases. An isolate of Trichoderma (Lou & Zhang 2005). Wang et al. (2007b) also from soil in Hebei Province exhibited control showed that the secretion of P. oligandrum distinctly efficiency of 80% in protecting cucumber seedlings suppressed the mycelial growth of P. sylvaticum on against P. aphanidermatum as a result of agar plates. The active compound had been isolated competition, growth within the hyphae, antibody and marketed as a biofungicide: polyversum which secretion and cell wall lysis of the pathogen. The had been found to increase the resistance to seedling effect was long-lasting and it even promoted the blight while promoting the growth of rice plants growth of cucumber seedlings (Tian et al. 2001). A (Ouyang et al. 2007). There were attempts to explore similar inhibitory mechanism existed in the control other approaches to the control of Pythium diseases. of turf grass Lolium perenne in Lanzhou by T. For example, six Chinese ectomycorrhizal fungi aureoviride (Gu et al. 2011). An isolate of T. (Boletus edulis, B. sp., Suillus grevillei, S. luteus, harzianum in Fujian Province reduced the growth Chromogomphus rutilus and Xerocomus rate of P. aphanidermatum by 80% in dual-culture chrysenteron), were found to be antagonistic to P. and the pot experiment results showed its control aphanidermatum and P. ultimum in vitro by effect on tobacco damping off was better than secreting substances to destroy the mycelia and

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inhibiting the formation of sporangia (Lei et al. Salvia splendens is listed as the host plant for P. 1995). Yu et al. (2008a) demonstrated that the splendens (Editorial Council 1996) without any extracts of Houttuyniae cordata inhibited the growth detail information. Most likely the disease was of P. ultimum and could be used to control root rot found in Taiwan (Anon. 1979). Although much has disease of pea caused by this pathogen. Secondary been learned about the occurrence and distribution metabolites (flavones, phenolics and spanonins), of Pythium in mainland China, more intensive from Solidago canadensis accumulated in soil and studies should be conducted to survey Pythium contributed to the inhibition of P. ultimum (Zhang et species in various parts of this vast country to further al. 2011). understand the diversity of the genus. Information of DISCUSSION Pythium species especially from virgin forest soil To date, 64 species of Pythium have been might shed light on the origin of those species reported from mainland whereas 48 and 28 species already discovered and help in the control of plant were found, respectively, in Taiwan and Hainan diseases caused by them. Island. Of the 64 Pythium species in mainland With the awareness of the adverse effects of China, 13 were described as new to the world: P. chemical fungicides on humans and the ecosystem, acrogynum, P. amasculinum, P. baisense, P. boreale, it is important to explore other non-chemical means P. breve, P. connatum, P. falciforme, P. guiyangense, to control Pythium diseases. The use of P. guangxiense, P. hypoandrum, P. kummingense, P. Trichoderma, P. oligandrum and antagonistic nanningense and P. sinensis, but only one new bacteria as seed dressings and soil amendment has species was found in Taiwan: P. s u ku ie n s e which has already been successfully adopted to suppress the not been reported from mainland China or Hainan pathogenic Pythium species and to induce resistance Island. None of the 13 new species from mainland in the host plants. It is possible to use molecular China has been found in Taiwan or Hainan Island. techniques to produce more potent and more stable The dominant species include P. aphanidermatum in strains of these antagonistic organisms. The recent mainland China, P. splendens, P. aphanidermatum, isolation of another mycoparasitic fungus, P. nunn is P. spinosum and P. acanthicum in Taiwan (Ho 2009, encouraging and there should be more efforts to 2011) and P. vexans in Hainan (Ho 2012). Most of make full use of this species in the control of soil the Pythium species in mainland China are borne plant pathogens. With further studies, pathogenic with 44 species parasitic on plants, one antagonistic extracts from plants and on the red alga, Porphyra yezoensis and two on ectomycorrhizae might one day become effective mosquito larvae: P. carolinanum and P. guiyangense. and practical biofungicides. It is intriguing that P. s p len de n s which is commonly Although P. aphanidermatum is probably the found in Taiwan causing a wide variety of plant most important plant-pathogenic species of Pythium diseases (Ho 2009) and in Hainan, infecting oil palm in mainland China it could be utilized to our seedlings by artificial inoculation (Chen et al. 2008) advantage. The crude extract of the fungus in liquid has been reported only twice in mainland China, culture proved to have herbicidal bioactivity and was from Guangxi Zhong Automonous Region (Yuan & toxic to a variety of weeds, including Digitaria Lai 2004) and Zhejiang Province (Wang et al. 1995). sanguinalis, Amaranthus retroflexus, Chenopodium

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album, Echinochlora crus-galli, Chloris virgata and production of useful compounds for human Setaria glauca (Zhang et al. 2005; Xu et al. 2008; consumption should be encouraged because of its Zhang et al. 2010d). The component 1 was isolated fast growth in liquid broth and high efficiency and from the extracts of the fungus and the results of low cost. For instance, eicospentacenoic acid is an bioassay suggested that it adversely affected the important unsaturated fatty acid widely used in photosynthesis of weeds (Xu et al. 2009b; Zhang et medicine, food and chemical industry because it has al. 2010d) were able to isolate and determine the many physiological functions in humans such as chemical composition of the toxin with at least one decreasing blood viscosity, preventing of the components to be dimethyl o-phthalate. It is arteriosclerosis as well as cardiovascular disease and hopeful that some time in the future a new has anti-cancer and anti-inflammatory properties. bioherbicide could be synthesized and used in the Thus Lu et al. (2008) studied the factors affecting field. Meanwhile, the toxin of P. aphanidermatum the fermentation of Pythium sp. in the production of had been used to rapidly screen turf grasses for eicospentacenoic acid. With further refinement of disease resistance (Yang et al. 2008). the fermentation technique it is hopeful that this and The discovery of two mosquito-killing species: other important compounds could be produced on a P. carolinianum and P. guiyangense has important large scale at a reasonable cost. implications. Since both have been found safe to non-target organisms, like animals, insects and crops Acknowledgments: Thanks are due to Dr. Zeng Hui-Cai it is about time to develop a comprehensive program of the Chinese Academy of Tropical Agricultural Sciences to apply them in the field in order to control in Hainan for the Chinese translation of the title and mosquitoes which not only are annoying to humans abstract of this article. in creating irritating bites but could be potential vectors for serious human diseases in various [REFERENCES] countries in the world, including dungue fever, Anon., 1979. A list of plant diseases in Taiwan. Plant Protection malaria, encephalitis, West Nile fever and yellow Society, Taiwan. 1-404 fever. Further studies are needed to understand their Bala K, Robideau GP, Levesque CA, de Cook AWAM, Abad ZG, pathogenesis in order to elucidate the mechanism Lodhi AM, Shahzad S, Ghaffar A, Coffey MD, 2010. involved in killing mosquito larvae. Since their DNA Phytopythium sindhum. Persoonia, 24: 136-137 libraries have been constructed it would be feasible Bridge PD, Newsham KK, Denton GJ, 2008. Snow mould caused to manipulate their genotypes via by a Pythium sp.: a potential vascular plant pathogen in the Agrobacterium-mediated mutations or isolate the maritime Antartic. Plant Pathology, 57: 1066-1072 virulence gene which can then be incorporated in Chai CS, He W, 2002. Investigation on the main lawn and turf other fungi more suitable for field application. diseases in summer in Beijing and a laboratory fungicide Should the mosquito larvae be killed by fungal selection experiment. Grassland of China, 24(6): 38-42 (in toxins it would be essential to isolate the active Chinese) component of the toxins in order to produce an Chai ZX, Li JH, Lou BG, Li W, Gan HL, Guo C, Zhao L, Dong D, effective mycoinsectide for the mosquitoes. 2009. Isolation, identification and sequence analysis of The utilization of Pythium species in the rDNA-ITS of Pythium species sampled from rhizosphere soil of

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