An Investigation of the Pathogenicity Characteristics of Magnaporthe grisea Isolates Collected from Different Host Plants from the Family Poaceae and on Race Determination of the Pathogenic Isolates

Thrity seven isolates of Magnaporthe grisea collected from several host plants from family of Poaceae namely Digitaria singuinalis, Setaria italica, and Echinochloa sp.were tested for their pathogenecity against two susceptible rice cultivars. Conidial suspensions were prepared by the surfaces of 14-day-old cultures being washed with sterile water and adjusting the final concentrations to approximately 5×104 conidia per ml with the aid of hematocytometer. Inoculums were applied to the leaves of 3 week-old plants and symptoms scrutinized 10 to 12 days following inoculation. Moreover, to confirm the outcomes of the test, the survey of the infection of the leaves was recapitulated after a 5 days interval. Pots each containing sixty seedlings of either Binam or Tarom rice cultivars were sprayed with 50 ml suspension of 5×104 conidia per ml from either pure cultures of the M. grisea or water, with a hand-held mist sprayer (until runoff) onto rice plants that were at a four-to-five-leaf stage. Inoculated plants were incubated in a humidity chamber and maintained at 100% relative humidity (RH) for 48 h and then reincubated in a greenhouse (20 to 24°C). Also negative and positive control plants were sprayed with distilled water and with rice infecting isolate respectively in the same manner. After 10 to 12 days past, leaf spot symptoms appeared on some inoculated plants. Then five virulent and semi virulent isolates as based upon their interaction with rice were analyzed for pathogenic races. In total 13 cultivars and lines (eight varieties differentiated through international standard cultivars and five through Near Isogenic Lines (NILS)) were examined. The last five isolates were classified in four pathogenic races IB-58, IA-27, IA-127, IA-17 that belonged to two race groups IA and IB as based on their virulence on eight international differential varieties, and in A, B, C, D as based on their virulence on five Near Isogenic Lines (NILS).