Background:
Bacterial blight (BB) of rice caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the major production constraint in major rice growing regions in India. Over the years, the intensity and geographic distribution of the disease has increased significantly. BB has become a major production constraint in many rice growing regions in south India. Analysis of pathogen population structure of Indian Xoo population has indicated that rice varieties with single BB resistance gene do not provide broad spectrum resistance to the disease necessitating the need of introgression of more than one BB resistance genes. Fine grain rice variety Samba Mahsuri is extremely popular among the farmers in south India and parts of Chhattishgarh, eastern Uttar Pradesh and parts of Bihar and Jharkhand. However, this variety is extremely susceptible to BB causing a significant amount of yield loss (to the extent of 50% or more depending on the severity of the disease and stage of infection). Therefore, three major BB resistance genes viz., Xa21, xa13 and xa5 were pyramided in the genetic background of Samba Mahsuri to provide a broad spectrum of resistance to BB:
Technology Details:
Improved Samba Mahsuri (RP Bio 226; IET 19046) is a durable bacterial blight (BB) resistant high yielding, fine grain type rice variety, suitable for irrigated rice ecosystem. The variety is same as Samba Mahsuri in all respects including grain and cooking quality with 100% in-built resistance to bacterial blight of rice. The variety has been developed jointly by Directorate of Rice Research (now ICAR-Indian Institute of Rice Research) and Centre for Cellular and Molecular Biology (CCMB) through marker assisted backcross breeding by pyramiding three bacterial blight resistance genes (xa5, xa13 and Xa21). The variety is a unique rice variety in the country and provides a broad and very high level of resistance against BB. Seeds of ISM were distributed to the rice farmers across the country through a CSIR sponsored project (CSIR 800/ CSIR-HARIT) called BLIGHT-OUT from 2013 onwards and has occupied a significant area in farmers’ field. Improved Samba Mahsuri has been registered as an extant variety with Protection of Plant Varieties and Farmers (PPV&FR) rights authority in 2010 and since then it has been licensed for seed production to two private seed companies. Recently, through clinical trials carried out by ICMR-National Institute of Nutrition, ISM has been determined to have low glycaemic (GI) index of 50.9, indicating its suitability for consumption by patients suffering from Type II diabetes. The variety has a yield potential of 5.5-6 t/ha. Under conditions of BB incidence, the variety shows a significant yield advantage of 15-30% compared to bacterial blight susceptible variety like Samba Mahsuri.