Morphological, physiological and biochemical studies on Pyricularia grisea isolates causing blast disease on finger millet in Ethiopia

Objective: Finger millet blast disease caused by Pyricularia grisea (Magnaporthe grisea) causes significant yield loss in Ethiopia. This study was conducted to isolate, identify and characterize the pathogen (using morphological, physiological and biochemical methods).Methodology and results: A total of 42 P. grisea isolates from five different finger millet producing regions of Ethiopia were collected from diseased finger millet plants and wild relatives. Based on their geographical distribution, virulence and comparative growth on culture media, only six isolates were selected for further indepth study. The morphological and physiological variability studies of the six isolates were carried out on Host Seed Extract + 2% Sucrose Agar, Oat Meal Agar, Potato Dextrose Agar and Richard’s Agar culture Media at varying temperature, pH, carbon and nitrogen sources. Each of the isolated P. grisea showed consistently better growth on Oat Meal Agar than other media. The isolates showed considerable variation in mycelial growth, pigmentation and conidia production in culture. Oat meal agar and Richard Agar media showed maximum mycelial growth with 87.3mm and 88.2mm by isolates of Pg 41 and Pg 26, respectively. Based on temperature preference and pH requirement, the isolates of P. grisea showed maximum mycelial growth of 61.4mm and 423.3mg at 30°C and pH 6.5. The isolates of P. grisea showed ability to metabolize a wide range of carbon and nitrogen sources among which dextrose and NaNO3 were the most suitable carbon and nitrogen sources for mycelial growth of all isolates. The variations in the utilization of the various carbon and nitrogen compounds seem to reflect inherent biochemical and physiological differences among P. grisea isolates.Conclusion and applications: Basic data on finger millet blast pathogen diversity and characterization using morphological, physiological and biochemical methods has been conducted. The results of this study help to understand the physiological and biochemical requirements for the growth and development of the pathogen, which could serve as an input in disease management to minimize the effect of blast disease on finger millet and its wild relatives.Keywords: Blast disease, Eleusine coracana, Pyricularia grisea, characterization