Pictorial Atlas of Soilborne Fungal Plant Pathogens and Diseases

Tsuneo Watanabe

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781351587884
• Edition: 1
• Topic: Scienze biologiche
• Subtopic: Botanica

The Pictorial Atlas of Soilborne Fungal Plant Pathogens and Diseases describes the soilborne fungal diseases caused by Oomycetes, Zygomycetes, Ascomycetes, Basidiomycetes, and Deuteromycetous (Anamorphic) fungi. Soilborne fungal diseases are significant as both environmental and agricultural problems, yet it is difficult to understand the ecology of pathogenic fungi and its effective control. This book provides very detailed information on many of the commonly and not so commonly encountered groups of soilborne fungi diseases. It will be a useful reference for those teaching and conducting research in mycology, plant pathology, soilborne plant diseases, and the ecology of fungal communities.

1 Aphanomyces and Plectospira

The genus Aphanomyces is characterized by forming zoospores, which move in a row inside hypha-like sporangia and encyst in a mass at the tips. Oogonia are terminal, often aggregated, include aplerotic oospores, and bear monoclinous antheridia suppressed often on coiled hypha-like antheridiumphores. Plant-pathogenic Aphanomyces species have been isolated from tissues of various host plants worldwide (Drechsler, 1929). A. cladogamous was isolated from tomato field soil or forest soil in Japan by bait methods with cucumber or lupinus seed.

The genus Plectospira is morphologically similar to the genus Aphanomyces. It forms lobate sporangia connected with hypha-like sporangia; and its zoospores, after moving in a row inside sporangia, encyst in a mass at the tips just like Aphanomyces. Oogonia is surrounded by monoclinous and diclinous hypha-like antheridia, including both plerotic and aplerotic oospores. Oospores are often formed without sexual contact of both oogonia and antheridia parthenogenetically.

Plectospira myriandra (isolate 84-209 (ATCC64139)) was first reported as tomato root isolates in the United States (Drechsler, 1927) and re-isolated in bamboo fields in Tosa, Japan 59 years after its discovery by the cucumber seed bait method (Watanabe, 1987); however, this fungus has now been commonly isolated from various areas in Brazil (Pires-Zottarelli, 2011) since its first record of isolation in Brazil (Gomez et al., 2003).

A. Damaged radishes harvested from a severely infected field in Akita.

B. Aphanomyces sp. associated with the underground disorder of radishes.

1.1 MORPHOLOGIES: APHANOMYCES

Aphanomyces cladogamous (isolate 83–413) (A–E)

A. Hypha-like sporangium bearing encysted zoospores at the tip.

B. Zoospores moving inside the exit tube, and two zoospores encysted outside.

C–D. Antheridia and oogonia bearing oospores.

E. Winding antheridiumphores, and antheridia surrounding oogonium, including single aplerotic oospore.

(Zoospores encysted 7–8 µm in diameter; oogonia 18.7–35 µm in diameter; oospores 15–25 µm in diameter)

1.2 MORPHOLOGIES: PLECTOSPIRA

Plectospira myriandra (isolate 84–209 (ATCC64139))

A. Zoospores encysted in a mass at the tip of an evacuation tube exit from lobate sporangium.

B. Oogonium surrounded with antheridia and lobate sporangium.

C–D. Oogonium covered with several antheridia diclinously and monoclinously.

E. Regermination from encysted zoospore.

F. Oogonium germinated elongating germ tubes.

G. Parthenogenetically formed oospore. Sporangia can reach up to 25 μm wide; oogonia can be 15–28 μm in diameter; and encysted zoospores can reach 5.5–15 μm.

(Watanabe, 1987)

1.3 PLECTOSPIRA MYRIANDRA

A. Radial mycelial growth rates of P. myriandra (isolate 84–209 (ATCC64139)) after incubation for 24 hours on corn meal agar culture under different temperatures.

B. Zoospore discharge (number of encysted zoospores/12.6 mm2) of P. myriandra under different temperatures.

C. Colony of P. myriandra (isolate 84–209, dried culture specimen).

(Watanabe, 1987)

2 Phytophthora

2.1 DISEASES: OVERVIEW

Phytophthora diseases occur commonly in Japan, including pineapple heart rot (A–B) in Okinawa, Phytophthora diseases of orchid (E) in Chiba, and Zanthoxylum piperitum (C–D) in Nara.

Pineapple heart rot (A–B)

The disease started rotting internally, and the basal rotted leaves were readily removable. The disease was caused by both P. nicotianae var. parasitica and P. cinnamomi.

Phytophthora disease of orchid (E)

The disease was caused by P. nicotianae var. parasitica. The blighted lesions occur abundantly on leaves.

Phytophthora disease of Zanthoxylum piperitum (C–D)

The diseased plants were discolored and weakened. The root systems were poor and also darkened. The disease was caused by an unidentified Phytophthora species.

Stem blight of rose

The hydroponic culture of rose seedlings was damaged for the first time in 1968 in Chiba, and plants showed wilting, yellowing, and defoliation (F). In pathogenicity tests, the three-month-old rooted cuttings inoculated by burying the inoculum of P. megasperma in the soil near the healthy cuttings grown in pots or dipping the roots in the inoculum suspension were seriously damaged, especially when artificially wounded prior to inoculation by cutting a part of the roots. The new shoots and lower leaves of the inoculated plants initially wilted (B) and the plants finally died (Nagai et al., 1978). The fungus was isolated for the first time by the crown-rot pathogen of hollyhocks by Drechsler (1931).

2.2 DISEASES: PINEAPPLE, CATTLEYA, ROSE

A–B. Pineapple heart...