Studies on BB Resistance Introgression in Aromatic Rice Variety Keteki Joha

Keteki joha, one of the most popular aromatic rice variety of our region was found to be resistant towards BB earlier, but is also becoming highly infested by the disease now a days.This may be due to the climatic change which may lead to the evolution of new races of the pathotype which might not exist earlier in Assam.Bacterial blight (BB) caused by Xanthomonas oryzae pv.oryzae (Xoo) is one of the most devastating diseases affecting entire rice acreages.It causes severe yield losses of up to 80% depending on the stage of the crop, cultivar susceptibility, and environmental conditions.An effectual and well founded chemical control method of the disease is not available.To save the crop from this deleterious disease, intensification of host plant resistance is the viable option, but it is hard to attain the required resistance through conventional breeding.Therefore the introgression of resistance genes of BB is the greatest possible way to tackle this disease and raise the productivity of the rice cultivation.The resistant varieties carrying resistance genes have been utilized to control the disease.A number of rice genes have been identified along with its closely linked microsatellite markers that confer resistance against X.Oryzae pv.oryzae.Out of these resistant genes -Xa4, xa5, xa13 and Xa21 have been introgressed in different combinations in the background of popular rice varieties of our country and exhibiting resistance by the introgressed varieties.Identification of parental polymorphism between the recipient and the donor variety is of prime importance to introgress the resistant gene.For introgression of Xa4, xa5, xa13 and Xa21, polymorphic molecular markers has been identified between the donor Improved Sambha Mahsuri and recipient Keteki joha; RM144 for Xa4, RM122 for xa5, xa13 for xa13 and pTa248 for Xa21.It was found that in Assam the prevalent pathotypes of X. oryzae pv.oryzae were III, V, VIII and IX.However, even after the presence of xa5 resistant gene which confers resistance against pathotypes V and VIII, Keteki Joha was found to be susceptible to BB infection, this may be due to evolution of new races III and IX.xa5 gene alone cannot confer complete resistance against the prevalent pathotype of Assam.Therefore, for complete resistance against the prevalent BB pathotype, a combination of other BB resistance genes-xa13 and Xa21 along with xa5 has to be introgressed.