Rhizoctonia solani Kuhn and other Rhizoctonia spp. are widespread in the world and in both cultivated and noncultivated soils. Rhizoctonia spp. are readily isolated from diseased plants and soils, with isolates differing in pathogenicity and morphology, as well as cultural and physiological charac­ teristics. Based on these differences, many species and intraspecific groups (ISGs) have been described; however, identification of species and ISGs is sometimes very difficult, owing to the absence of the authentic cultures, which hinders mycological and pathological studies. Fortunately, this situa­ tion has been put in order through the efforts of many researchers through characterization of the genus Rhizoctonia, the species R. solani, and other Rhizoctonia spp. The introduction of the concept of anastomosis groups (AGs) or intraspecific groups, as this paper introduces, has also aided species and subspecies identification. Ecologically, Rhizoctonia spp. are diversified; they may be pathogens on many hosts, saprophytes in soils, or mycorrhizae of orchidiaceous plants. This paper outlines the present status of our knowledge of ecology and pathology of Rhizoctonia solani, especially of anastomosis groups or in­ traspecific groups.

Ecology and pathogenicity of anastomosis and intraspecific groups of

Soilborne, fungal pathogens of cool season food legumes, including seed and seedling blights, rot rots, and wilts are described. Seed and seedling diseases are caused primarily by Pythium and Rhizoctonia spp. The most important fungi causing root rots include Aphanomyces euteiches, Fusarium solani, Pythium spp., Sclerotium rolfsii, and Macrophomina phaseolina. Wilt is caused primarily by various host-specific forms of Fusarium oxysporum. This paper discusses these diseases and screening procedures that emphasize standardization of inoculum levels, maintenance of virulent pathogen cultures, inoculum growth media, environmental conditions, and host plant age. Sources of resistance to these diseases are discussed.

Screening techniques and sources of resistance to root rots and wilts in cool season food legumes.

Among Rhizoctonia species, the following have been reported to cause diseases on vegetable crops. R. solani AGs 1 to AG 5 and binucleate Rhizoctonia AGs-E, -F and - R. Different symptoms are caused by different specified Rhizoctonia isolates. For examples, aerial blight or web blight are caused by R. solani AG 1 (Yang et al., 1990), AG 2-3 (Naito and Kanematsu, 1994) and AG 3 (Date et al., 1984). Damping-off, stem or root rot are mainly caused by AG 2 (Naiki and Kanoh, 1978; Liu and Sinclair, 1991), AG 4 (Win and Sumner, 1988) and AG 5 (Naiki and Ui, 1981). The hypocotyl rot is induced by AGs 1, 2, 4, and E (Warren et al., 1972; Galindo et al., 1982; Ploetz et al., 1985). In order to control diseases caused by different AGs of Rhizoctonia spp., the ecological manner of different Rhizoctonia isolates will be seriously considered and realized. In this paper, the Rhizoctonia diseases of major vegetable crops are demonstrated.

Vegetable Diseases Incited by Rhizoctonia Spp.

Mycoflora of pea seeds and the effectiveness of Rhizobium leguminosarum on important seed-borne pathogens were determined. Mycoflora were changed according to seed groups with or without surface sterilization. The most common isolated fungi were Fusarium spp., Alternaria spp., Macrophomina phaseolina, Phytophthora megasperma , Rhizoctonia solani and Sclerotium rolfsii. R. leguminosarum showed antagonistic effect on Fusarium oxysporum and P. megasperma by 66.3 and 62.1%, respectively, in dual culture test in vitro . R. leguminosarum application reduced disease severity of P. megasperma , R. solani , F. oxysporum and S. rolfsii by 52.9, 50, 67.9 and 52%, respectively. Results indicated that R. leguminosarum showed effects on plant pathogenic fungi and could be used as biocontrol agent.

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Determination of mycoflora of pea (Pisum sativum ) seeds and the effects of Rhizobium leguminosorum on fungal pathogens of peas

Rhizoctonia solani Kuhn and other Rhizoctonia spp. are the plant pathogenic fungi widespread in the world and in both cultivated and noncultivated soils. Rhizoctonia spp. are readily isolated from diseased plants and soils, which differ in their pathogenicity, cultural, morphological and physiological characteristics. Identification of species and intraspecific groups (ISGs) is sometimes very difficult, due to the absence of the authentic cultures, which hinders mycological and pathological studies. The genus Rhizoctonia can be identified using various techniques such as, sequence analysis of ITS regions, DNA fingerprinting and the rDNA coding sequence. The introduction of the concept of anastomosis groups (AGs) or intraspecific groups has also aided species and subspecies identification. There are 13 different anastomosis groups exists in Rhizoctonia solani of which AG 1-4 were strong pathogenic on many plants and AG 6-10 were orchid mycorrhizae. Analysis of restriction fragment length polymorphisms (RFLPs) and the sequences within ribosomal RNA genes (rDNA) among different anastomosis groups of R. solani isolates exhibited DNA base sequence homology and diverging evolutionary affinities for hyphal anastomosis. More recently, ribosomal DNA (rDNA) sequences have been used to study the genetic relationships between AG of R. solani. The ecology and epidemiology of each ISG of R. solani must be investigated in order to gain a better understanding of this important group of fungi.

https://www.phytojournal.com/archives/2021/vol10issue2/PartF/10-1-377-257.pdf

R. J. Mccoy

Papers

Resistance in Pisum sativum to epicotyl rot caused by Rhizoctonia solani