Pyricularia oryzae pathogenicity

Melanin is a collective term for brown or black pigments. They are condensates of phenolics and are widely distributed in nature, examples of this diverse chemistry being found in animals, plants and fungi. They perform various roles but in some fungi, notably Pyricularia oryzae and Colletotrichum spp., melanin biosynthesis is an essential feature in pathogenicity, the biosynthesis of melanin in appressorial walls being a requirement for the development of infection hyphae and subsequent penetration of the host epidermis. For example, melanin-deficient mutants of P. oryzae are not pathogenic. 

Probenazole is used for the control of Pyricularia oryzae in rice (Figure 4.40). Interestingly, probenazole is ineffective against P. oryzae as a pathogen of barley, implying a dependence upon the metabolism of the natural host, rice, or a different SAR response. 

When we started to look for the mode of action of different EBI s, we decided to use several pathogens as test organisms. These were Pyricularia oryzae, Botrytis cinerea, Cercospora musae, Fusarium nivale, and Drechslera teres. To get rapid information about the possible antimycotic efficacy of a test compound, we also used a non-pathogenic yeast, Saccharomycopsis lipolytica. 

Blasticidin S. Blasticidin S is the first successful agricultural antibiotic developed in Japan. It was isolated from the culture filtrates of Streptomyces griseochromogenes by Takeuchi et al. (7), and the potent curative effect of blasticidin S on rice blast was found by Misato et al. (8) Thereafter the benzyl-aminobenzene sulfonate of blasticidin S was reported to be least phytotoxic to the host plant without reducing antifungal activity against Pyricularia oryzae, the pathogen of rice blast (9), and... 

Melanin Biosynthesis Inhibitors. Among the most desirable targets for selective fungitoxic action are those uniquely associated with fungal pathogenicity such as the polyketide pathway to melanin in the fungus Pyricularia oryzae which causes rice blast disease. 

Various biochemical approaches to the pathogen-ecity of Pyricularia oryzae, a rice blast fungus, have been studied in our laboratory from the stand points of toxins (1,2) and glycosidases produced... 

The microbial cultures of isolates and their antifungal agents strongly inhibited growth of F. oxysporum and also many other plant pathogenic fungi F. solani, F. moniliforme, F. roseum, Biporaris sorokiniana, Alternaria alternata, Cladosporium cucumerinum, Pyricularia oryzae, Pythium graminicolum, Verticillium dahliae, Cylindrocarpon sp., Rhizoctonia soIani(Table III, IV). 

Several compounds such as fusaric acid (52) and a-picoli-nic acid (53) (Fig. 29.18) (from the pathogenic fungi Fu-sarium oxyspomm and Pyricularia oryzae, respectively) are phytotoxins. Both are probably involved in chelation of ferric and zinc ions (Stoessl, 1981). 

Pyricularia oryzae in rice (Oryza sativa) [253]. When the stilbene synthase gene from peanut (Arachis hypogaea) was overexpressed in alfalfa, the transgenic plants accumulated piceid and showed increased resistance to the alfalfa pathogen, Phoma medicaginis [155]. 

The cellulase activities Q and C have been detected in filtrates of germinating conidiospores and in growing mycelia of pathogenic and non-pathogenic strains of Pyricularia oryzae, Comparisons of these activities for various strains of P. oryzae grown on rice-plant powder showed that the Ci activity is related to the pathogenicity. 

Chitosan has been used also as carriers for synthetic fungicides against Pyricularia oryzae and Rhizoctoria solani. A mixture of equal weight of chitosan and fungicide has the same effect on pathogens as fungicide used alone and less toxic. 

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