P-188 - Molecular mapping of an avirulence gene of Pyricularia oryzae Eleusine pathotype on wheat

Pyricularia oryzae, a causal agent of blast disease on various gramineous plants, is composed of pathotypes that show host specificity at the plant genus level. The avirulence of Eleusine pathotype (specific to finger millet) on common wheat is controlled by at least five genes including PWT3, PWT6, and PWT7. Analyzing genes involved in the incompatibility between the Eleusine pathotype and wheat could provide key insights into the evolutionary process leading to the emergence of the Triticum pathotype. Therefore, we attempted to clone one of the five avirulence genes, eA2, which confers avirulence of the Eleusine pathotype on common wheat. 200R39, an F₁ culture derived from MZ5-1-6 (an Eleusine isolate) x Br48 (a Triticum isolate), was backcrossed with Br48 twice. When the resulting BC₂F₁ cultures were sprayed onto the wheat cultivars Hope and Anahuac (Ahc), avirulent and virulent cultures segregated in a 1:1 ratio with the same segregation pattern. On cultivars Transfed (Tfed) and Langdon (Ldn), the segregation ratio was 3:1. The isolates avirulent on Hope and Ahc were also avirulent on Tfed and Ldn, suggesting that a single gene controls avirulence on all these cultivars. Bulked segregant analysis and molecular marker-based mapping revealed that eA2 is located on chromosome 1 of MZ5-1-6. These findings suggest that the loss of eA2 function played a crucial role in the adaptation of P. oryzae toward wheat.