Irradiation of Wheat Seeds for Developing Mutants Resistant to Blast (Magnaporthe oryzae Triticum)

Seeds of four wheat BARI Gom varieties were irradiated with four different doses of Gamma rays (150Gy, 200Gy, 250Gy, 300Gy). Both M 1 and M 2 population were exposed to wheat blast under natural field condition. In the present study, M 3 seeds harvested off M 2 population were grown under both confined inoculated and natural field condition. In BINA campus, M 3 plants were inoculated with spore load (CFU 1×10 7 spores/ml) of Magnaporthe oryzae Triticum (MoT) at pre-heading stage (53 days age). Inoculation was repeated thrice to cover pre-heading stage of some late mutants. In Madnadanga Meherpur Sadar, M 3 population was exposed to blast infection under natural field condition in the farmer’s field. Among the radiation doses, 200Gy produced significant reduction in MoT infection. Inoculated M 3 plants showed differential reaction to Magnaporthe infection. Only one entry (BWM 5) was completely free of blast infection. Another one entry (BWM 6) carried only 0.13 % blast severity. Eight entries (BWM 2, 3, 7, 9, 20, 21, 22, 23) had <5% blast severity while other four entries had< 10% blast severity. Here blast severity means percent spike surface area bleached. Molecular analysis in PCR done with MoT3 marker produced typical bands of MoT (361 bp) in all the entries except for the entry BWM 5. In Madnadanga farmer’s field, blast disease pressure was very low; most of the entries did not catch infection. Entry BWM 5 and entry BWM 6 and some other 12 entries which showed 0-10% blast severity indicated the inheritance of blast resistance which needs advancing through further checking under inoculated epiphytotic condition.