菌物学报 [email protected] 8 April 2013, 32（增刊）: 20-44 Http://journals.im.ac.cn Mycosystema ISSN1672-6472 CN11-5180/Q © 2013 IMCAS, all rights reserved. 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 菌物学报 22 ISSN1672-6472 CN11-5180/Q Mycosystema April 8, 2013 Vol.32 (Suppl.) 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. http://journals.im.ac.cn/jwxtcn HO Hon-Hing / The genus Pythium in mainland China 23 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: