Brown Root Rot Caused by Phellinus Noxius in Subtropical Areas of Japan

102 年森林健康之管理與經營國際研討會 2013 International Symposium on Forest Health Management

Brown root rot caused by Phellinus noxius in subtropical areas of Japan

Norio Sahashi

Department of Forest Microbiology, Forestry and Forest Products Research Institute (FFPRI)

ABSTRACT The fungus Phellinus noxius has a broad host range and causes brown root rot in a variety of tree species of various ages, irrespective of their original health. The fungus is widely distributed in tropical countries of Southeast Asia, Oceania, Central America and Caribbean, and Africa. Since 1988 when brown root rot was first found on Ishigaki Island, Okinawa Prefecture, the disease has been reported on several islands in the Ryukyu (Nansei) Islands and the Ogasawara Islands, and it has been causing serious problems to shade, windbreak, ornamental, and landscape trees in the subtropical region of southern Japan.

Here, I report on the current status of P. noxius-caused brown root rot in subtropical areas of Japan, including symptoms, distribution and host tree species of the disease, and pathogenicity and/or virulence of the pathogen based on our surveys and previously published reports from Japan. In the Ryukyu Islands, brown root rot has been confirmed in 53 tree species from 32 plant families at different sites on 10 of the 12 islands surveyed. Among the 53 tree species, 34 were first recorded in Japan as host plants of P. noxius. In the Ogasawara Islands, we confirmed brown root rot in 33 tree species from 20 plant families．Among them, 20 tree species were first recorded in Japan as host plants, including endemic species of the Ogasawara Islands. The disease occurs mainly in shade, windbreak, and ornamental or landscape trees at scenic areas, parks, roadsides, agricultural land such as sugar cane fields and around residences or other places associated with human activities.

Key Words: brown root rot, Phellinus noxius, The Ryukyu Islands, The Ogasawara Islands, Subtropical areas of Japan

Corresponding E-mail：[email protected]

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Introduction

Phellinus noxius (Corner) G. Cunn. is widespread in tropical countries of Southeast Asia, Oceania, Central America and Caribbean, and Africa, where it causes brown root rot in a variety of trees of all ages and health conditions (Singh et al. 1980; Bolland 1984; Hodges and Tenorio 1984; Neil 1986, 1988; Nandris et al. 1987a; Arentz and Simpson 1989; Bolland et al. 1989; Dennis 1992; CABI/EPPO 1997; Quanten 1997; Chang and Yang 1998; Larsen and Cobb-Poulle 1990; Ann et al. 2002; Brooks 2002; Albrecht and Venette 2008). The fungus has a very wide host range (Bolland 1984; Hodges and Tenorio 1984), with more than 200 woody plant species representing 59 families currently reported as host plants worldwide (Ann et al. 2002).

In Japan, brown root rot was first found in windbreak trees on Ishigaki Island, Okinawa Prefecture, in 1988 (Abe et al. 1995; Fig. 1). Since then, the disease has been reported on several islands in both the Ryukyu and the Ogasawara Islands, causing serious problems to shade, windbreak, and ornamental or landscape trees in subtropical regions of southern Japan (Kobayashi and Kawabe 1991; Kobayashi et al. 1991; Kawabe et al. 1993; Hattori et al. 1996; Kobayashi and Kameyama 2002; Sahashi et al. 2007, 2012, 2013; Shimada et al. 2013; Kawabe 2010).

Here, I report on the current status of P. noxius-caused brown root rot in subtropical areas, the Ryukyu Islands and the Ogasawara Islands, Japan, as well as general information about the disease, based on our surveys and previously published reports.

Characteristics of the pathogen

Phellinus noxius, a causal pathogen of brown root rot, is easily isolated from root tissues of newly dead or declining trees at a relatively high frequency after incubation of flame-sterilized pieces of affected tissues (Sahashi et al. 2007, 2012, Fig 2a). On potato sucrose agar (PSA), the fungus first produces a white colony, which turns brown, with irregular dark brown lines or patches (Fig. 2b). Arthrospores and

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Fig. 1. Geographic distribution of brown root rot caused by Phellinus noxius in the Ryukyu Islands. Red circles indicate sites where the disease has been confirmed in our 13 field surveys. Each number on left side map is corresponding to each island indicated by the same number on right side. The precise locations of each island are indicated in left side map.

Fig. 2. Cultural characteristics of Phellinus noxius. (a) Colonies growing up from small pieces of decayed wood. (b) Colony morphology on potato sucrose agar (PSA) with irregular dark brown patches. (c) Arthroconidia produced on PSA. (d) Staghorn-like hyphae produced on PSA.

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staghorn-like hyphae (Fig. 2c, d) are commonly observed in culture. The pathogen can grow at temperatures between 12-13 to 37 ºC, with the optimal temperature near 30 ºC (Abe et al. 1995; Ann et al.1999). Fruiting bodies of P. noxius are rarely observed on diseased trees in the field (Sahashi, 2007, 2012). Similar observations have been reported from Taiwan (Chang and Yang 1998; Ann et al. 1999, 2002; Chang, T. T. 2002), which is very close to Okinawa, and from West Africa (Nandris et al. 1987a).

Disease symptoms

Brown root rot has been observed on a variety of tree species of various ages and health conditions in Japan (Table 1). Infected trees usually exhibit reduced growth, discoloration and wilting of the foliage, defoliation, and dieback of branches, after which whole plant eventually dies (Figs. 3, 4). These symptoms are similar to decline symptoms caused by other root rot pathogens. However, these aboveground symptoms and the rate of their development may vary considerably depending on tree species, age, and possibly environmental conditions (Fig. 3). Generally, young trees show rapid tree death, while older trees exhibit more gradual decline.

In contrast to foliage symptoms, belowground (root) symptoms are quite unique, and differ from those caused by other root rot pathogens, such as Rigidoporus microporus (Sw.) Overeem (syn. R. lignosus (Klotzsch) Imaz.) and Armillaria spp. (Bolland 1984; Nandris et al. 1987a, b; Intini, 1991; Mohd Farid et al. 2009). A thick mycelial sheath or crust with first a cinnamon, then a dark-brown to blackish color appears on the surface of the affected stem base (Fig. 5a, b). The encrustation may extend up to 2 m above the ground level in tropical countries (Hodges and Tenorio 1984; Singh et al. 1980), but does not grow that high in Japan except for several cases in the Ogasawara Islands. Diseased roots are also covered with a brown to black mycelial crust (Fig. 5d, f, h), with soil particles and small stones usually adhered tightly to or embedded in the mycelial crust. Infected wood becomes brown at first (Fig. 5e), but in the late stage it forms a soft textured white rot, with conspicuous brown lines irregularly distributed in the decaying tissue, yielding a honeycomb appearance (Fig. 5c, g, i, j). A thin white to brown mycelial mat is usually present between the bark and wood (Fig. 5 k).

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Table 1. Host records of brown root rot caused by Phellinus noxius in the Ryukyu Islands, Japan

Reported as Location Plant families Plant species References2) new hosts （Island)1)

1 Anacardiaceae Rhus succedanea a3) 1 9

2 Apocynaceae Cerbera manghas 6 10

3 Aquifoliaceae Ilex rotunda a 3 9

4 Araliaceae Aralia elata a 1 9

5 Berberidaceae Nandina domestica a 3 9

6 Bombacaceae Chorisia speciosa a 8 1,3,5,10

7 Boraginaceae Argusia argentea a 8 10

8 Ehretia dichotoma a 9 10

9 Buxaceae Buxus bodinieri a 6 10

10 Casuarinaceae Casuarina equisetiforia a 1,2,3,4,6,7,8,9,10 1,2,3,4,5,7,8,9,10

11 Celastraceae Maytenus diversifolia a 7 10

12 Clusiaceae Calophyllum inophyllum a 6,8,9 1,3,7,10

13 Garcinia subelliptica a 9 3,7,10

14 Ebenaceae Diospyros ferrea var. 9 10 buxifolia 15 Elaeocarpaceae Elaeocarpus sylvestris a 1,7 9, 10 var.ellipticus 16 Euphorbiaceae Bischofia javanica 2 10

17 Glochidion obovatum a 1 9

18 Jatropha pandurifolia a 8 4

19 Macaranga tanarius 8,10 10

20 Hamamelidaceae Distylium racemosum a 6 10

21 Hernandiaceae Hernadia nymphaeifolia 4 9

22 Lauraceae Cinnamomum a 6,7 10 doederleinii 23 Cinnamomum japonicum a 1,2,3,4,5,7,8 9, 10

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Reported as Location Plant families Plant species References2) new hosts （Island)1)

24 Litsea japonica a 1,2,3,5 9,10

25 Machilus thunbergii a 1,7 9, 10

26 Leguminosae Acacia confusa a 8,9 1,3,7,10

30 Bauhinia acuminata a 8 4

31 Bauhinia racemosa a 9 3,7

27 Bauhinia variegata 6 10

32 Delonix regia 9 3,6,7

28 Erythrina variegata 8,9 3,7,10

29 Leucaena leucocephala 9,8,10 1,10

33 Lythraceae Lagerstroemia subcostata a 1 9

34 Malvaceae Hibiscus rosa-sinensis 5,9 1,9

35 Hibiscus tiliaceus 2,6 10

36 Meliaceae Melia azedarach var. 10 10 subtripinnata 37 Moraceae Ficus microcarpa 4,10 9, 10

38 Ficus virgata a 4 9

39 Morus australis a 1 9

40 Myrsinaceae Ardisia sieboldii a 3 9

41 Myrtaceae Eugenia uniflora a 9 10

42 Eucalyptus sp. 6 4

43 Oleaceae Ligustrum japonicum a 1 9

44 Palmae Areca catechu a 8 4

45 Pittosporaceae Pittosporum tobira a 1 10

46 Podocarpaceae Podocarpus macrophyllus a 1,9 3,7,9,10

47 Rosaceae Prunus cerasoides var. 7 10 campanulata 48 Prunus persica 1 9

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Reported as Location Plant families Plant species References2) new hosts （Island)1)

49 Rhaphiolepis indica var. a 1,3,4,6 9, 10 umbellata 50 Rutaceae Murraya paniculata 3 9

51 Sapindaceae Litchi chinensis 6 10

52 Verbenaceae Callicarpa japonica var. a 10 10 luxurians 53 Duranta repens 10 10

1) Locations provided on map in Fig. 1. 2) 1.Kawabe et al., 1993; 2.Kawabe et al.,1990; 3.Kobayashi et al.,1991; 4.Kobayashi and Kameyama, 2002; 5.Kobayashi and Kawabe, 1991;6.Kobayashi et al.,1995; 7.Kobayashi et al., 1989; 8.Kobayashi et al., 2007; 9.Sahashi et al. 2007; 10.Sahashi et al．2012 3) First reported in Japan.

Fig. 3. Aboveground symptoms of declining or dead trees infected with Phellinus noxius. (a) Ficus microcarpa, (b) Cinnamonum japonicum, (c) Pittosporum tobira tree showing rapid leaf wilting next to dead Casuarina equisetifolia, (d) Calophyllum inophyllum, (e) Cinnamomum doederleinii and (f) Declining Casuarina equisetifolia, with thinning of the crown and reduced growth. Trees (a, b, d and e) were growing on roadsides or near residences. 7 102 年森林健康之管理與經營國際研討會 2013 International Symposium on Forest Health Management

Fig. 4. Brown root rot in a number of adjacent trees. (a, c, d) Large gaps in windbreaks of Casuarina equisetifolia resulting from tree deaths caused by P. n o x i u s . (b) Brown root rot in hedge of Rhaphiolepis indica var. umbellata. (e) Small focus of the disease affecting Acacia confusa and other trees. The disease spread to adjacent trees in the direction of the arrow.

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Fig. 5. Characteristic symptoms of root and stem base infected with Phellinus noxius. (a, b) Thick mycelial crust with brown to black color on the stem bases of Cinnamomum japonicum (a) and Calophyllum inophyllum (b). (d, f, h) Outer surface of lateral roots covered with mycelial mat with soil: Rhaphiolepis indica var. umbellate (d), Cinnamomum japonicum (f), and Podocarpus macrophyllus (h, artificial inoculation). (e, g) Appearance of wood beneath the bark in early (e) and late (g) stages of decay. (c, i, j) Well developed white rot with conspicuous brown lines permeating rotted wood of Casuarina equisetifolia (c), Rhaphiolepis indica var. umbellata (i), and Chorisia speciosa (j). (k) White mycelial mat growing on the inner bark surface of Rhaphiolepis indica var. umbellata. 102 年森林健康之管理與經營國際研討會 2013 International Symposium on Forest Health Management

Distribution and host species of the disease

Host plants in the Ryukyu Islands of brown root rot caused by P. noxius are listed in Table 1 on the basis of previous reports from Japan (Kobayashi et al. 1989; Kawabe et al. 1990; Kobayashi and Kawabe 1991; Kobayashi et al. 1991; Kawabe et al. 1993; Kobayashi et al. 1995; Kobayashi and Kameyama 2002; Kobayashi et al., 2007; Sahashi et al. 2007, 2012). Currently, brown root rot has been confirmed in 53 tree species from 32 plant families at different sites on 10 of the 12 islands surveyed (Fig. 1). To our knowledge, Oshima Island is currently the northernmost recorded distribution of the disease in the Northern Hemisphere (Sahashi et al. 2007). Brown root rot is very common in angiosperm trees and has been confirmed in only one gymnosperm species, Podocarpus macrophyllus (Thunb.) D. Don. Among the 53 tree species, 34 were first recorded in Japan as host plants of P. noxius. Recently, we confirmed brown root rot in 33 tree species from 20 plant families in Ogasawara Islands (Sahashi et al. 2013, Shimada et al. 2013). The host plants observed in Ogasawara Islands included endemic species of the Islands.

The disease occurs mainly in shade, ornamental, and windbreak trees at sightseeing places, parks, roadsides, agricultural land such as sugar cane fields and around residences or other places associated with human activities. The disease has never been found in natural forest except for several cases in Ogasawara Islands, which agrees with observations elsewhere (Chang 1995; Ann et al. 2002). The disease is more often observed in low-elevation plains and hills less than 100 m above sea level than in high mountainous forests; this distribution pattern also agrees with previous findings (Chang and Yang 1998; Ann et al. 2002; Chang 2002). While P. noxius has been found in broken or fallen trees in Ryukyu Islands forests, these occurrences never became a disease center or focus (Hattori, personal communication). Singh et al. (1980) also reported that P. noxius occurred and attacked trees in natural forests in Fiji, but infection centers were limited to small areas. In natural forests, equilibrium is established among species that compose the microflora through competition and other methods. Human disturbance (e.g. clear cutting, forest road/trail construction) might destroy this equilibrium and cause

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instability in the microbial ecosystem, perhaps creating favorable conditions for the brown root rot pathogen.

Pathogenicity, host specificity and virulence of the pathogen

The pathogenicity and virulence of P. noxius in several countries has been reported (Bolland 1984; Nandris 1987b; Dennis 1994; Abe et al. 1995; Chang 1995; Ann et al. 1999; Mohd Farid et al. 2001, 2009; Supriadi et al. 2004). However, most host species that have been reported from Japan have not been shown experimentally via pathogenicity tests to be susceptible to P. noxius, and no information on host specificity or virulence of the pathogen is available.

Recently, cross inoculation tests with nine isolates of P. no x i u s from different tree species in the Ryukyu Islands revealed that the fungus was pathogenic to all nine tree species tested and all species experienced some mortality (Fig. 6a-g, Sahashi et al. 2010). Apparent host specificity of the fungus was not confirmed. These results are consistent with previous findings from Taiwan (Chang 1995; Ann et al. 1999), in which several P. noxius isolates from different hosts were used to inoculate each of the host species.

In contrast to host specificity, the virulence of P. noxius isolates was quite variable as has been reported by Nandris et al. (1987b) and Nicole et al. (1985), who found variable virulence or pathogenicity to Hevea brasiliensis seedlings was found among P. noxius isolates from West Africa.

Recently we carried out preliminary inoculation experiment to verify the pathogenicity of P. noxius from Japan to four important coniferous plantation species (Chamaecyparis obtusa (Sieb. et Zucc.) Endl., Cryptomeria japonica (L. f.) D. Don, Larix kaempferi (Lamb.) Carr. and Pinus thunbergii Parl.). Phellinus noxius from Japan was pathogenic to four coniferous species tested, and it was able to kill these species (Fig. 6h-k), although mortality was variable (10-100 %) depending on tree species and isolate of P. noxius used (unpublished data).

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Fig. 6. Rapid wilt and leaf discoloration in trees infected with Phellinus noxius 30 days after inoculation. a, Rhaphiolepis indica var. umbellata; b, Machilus thunbergii; c, Cinnamomum japonicum; d, Casuarina equisetifolia; e, Melia azedarach var. subtripinnata; f, Podocarpus macrophyllus; g, Calophyllum inophyllum; h, Pinus thunbergii; i, Larix kaempferi; j, Cryptomeria japonica: k, Chamaecyparis obtusa.

Based on these studies, we consider that P. noxius isolates from Japan have a broad host range without any host specificity, and have different virulence among isolates. However a comprehensive study, with more isolates of P. noxius from various countries and from many tree species, should be conducted to better understand the host specificity and virulence of the fungus.

We are developing easy and quick inoculation method to evaluate pathogenicity and/or virulence of the pathogen and to choose resistant tree species or variety.

The development of improved modes of transportation has increased the movement of tree seedlings and other plant materials in Japan, as well as globally. Thus, P. noxius could invade Kyushu and Honshu (the largest island of Japan) from the Ryukyu Islands or foreign countries via shipments of seedlings and their related materials, such as soil. (Abe et al. 1995) showed experimentally that the fungus was able to survive winter and kill trees in warm temperate area of Japan. Thus, if the fungus is introduced into Kyushu and Honshu islands of Japan, there could be a

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possibility of causing serious damage. Global warming may also promote damage because the pathogen prefers tropical or subtropical climates (Abe et al. 1995). To prevent the invasion of the pathogen, it is necessary to construct a strict monitoring system.

Finally, we should conduct following studies for better understanding and controlling this important disease.

1. Clarifying the genetic structure within and among the Ogasawara and the Ryukyu islands, (possibly among the other pacific islands). 2. Determining environmental factors and/or other factors that contribute to this disease. 3. Developing the control procedures of this disease.

Acknowledgements

I thank M. Akiba, Y. Ota, N. Kanzaki, T. Hattori, Forestry and Forest Products Research Institute (FFPRI), M. Ishihara, Hokkaido Research Center, FFPRI and H. Masuya, Tohoku Research Center, FFPRI for their kind help throughout the investigation, valuable suggestions and comments.

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日本亞熱帶地區由木層孔菌(Phellinus noxius)所引起之褐根

腐病

佐橋憲生日本國立林業和森林產品研究所

摘要木層孔菌 (Phellinus noxius)具廣泛之寄主範圍，可引起許多林木不同樹齡之褐根腐病，而與其原來健康與否無關。此病原真菌廣泛分布於熱帶地區，如位於南亞、中美洲加勒比海和非洲等地之國家。在日本於 1988 年首次於石垣群島，沖繩縣被發現，其後陸續於琉球群島和小笠原群島被報導，嚴重為害位於日本南方亞熱帶地區之行道樹、防風林、觀賞作物以及景觀樹木。在此，基於調查和以前業已發表之論文，報導 P. noxius 於日本亞熱帶地區之褐根腐病，包括其病徵、分布、寄主樹種以及其病原性和致病性。在琉球群島，所調查之 12 個島中之 10 個島，計 32 科 53 種之林木證實有褐根腐之發生，而 54 種中之 34 種林木為首次之記錄；而於小笠原群島也證實 22 科 33 種林木被此木層孔菌 P. noxius 侵染，其中包括首次發現之 20 種林木以及小笠原群島之特有種。此病害主要發生於遮陰、防風、觀賞、景觀以及行道樹或農地，住宅區之林木。

關鍵詞：褐根腐病、Phellinus noxius、琉球群島、小笠原群島、日本亞熱帶地區