Pathogenic Variation and Molecular Characterization of Pyricularia oryzae, Causal Agent of Rice Blast Disease in Tanzania

Rice blast disease, caused by the fungus Pyricularia oryzae, is one of the most devastating diseases of rice. Understanding pathogenic variation and molecular characterization of P. oryzae is one of the most efficient ways to manage the disease. Studies on identification, characterization and pathogenic variation of P. oryzae were conducted in the laboratory and screen-house at Sokoine University of Agriculture, Morogoro. Seven P. oryzae strains collected from Shinyanga, Kilimanjaro, Mbeya and Morogoro were tested with a set of ten rice blast differentials viz; IRBLk-Ka, IRBLkm-Ts, IRBLb-w/co, IRBLkp-K60, IRBLz-Fu, IRBLa-C, IRBLi-F5, IRBLta2-Pi), St and IRBLt-K59. Twenty one-day-old seedlings grown in pots were inoculated with spore suspension of a P. oryzae at a concentration of 2 x 10 ml -1 using a hand-hold sprayer in the evening. Considerable pathogenic variations among the tested strains were observed. The International rice differentials IRBLk-Ka, IRBLkp-K60, IRBLa-C, IRBLi-F5, IRBLta2-Pi, St and IRBLt-K59 were resistant to all strains, however, IRBLb-w/co, IRBLkm-Ts and IRBLz-Fu (Piz) were susceptible. Molecular analysis using four primers Bt1a and Bt1b, CAL-228F and CAL-737R, ACT-512F and ACT-783R, ITS1 and ITS4 were used for amplification of seven P. oryzae strains. The results showed no differences in banding patterns between strains, indicating that all strains analyzed were genetically homogeneous but pathogenically heterogeneous.