Abstract
Rice is food for more than half of the world population and the most consumable cereal in most of the countries. Pakistan is the fifth largest exporter of rice. However, Bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae is the most devastating and serious threat to rice production in many countries of the world including Pakistan. To combat this disease, innate genetic resistance of the plant plays vital role along with being environmentally friendly and economical. In this study, thirty-one (31) Near Isogenic Lines (NILs) having Xa4, xa5, Xa7, xa13 and Xa21 reported BLB tolerant genes and 34 locally developed rice lines were investigated under natural field conditions at three agro-ecologically different locations with highest disease occurrence records (BLB hotspots) viz., Sheikhupura, Hafizabad and Gujranwala, Punjab, Pakistan in order to assess their respective genetic resistance and G × E interactions against the disease. Thirty-one (31) lines were categorized under resistant cluster, twenty-eight (28) were moderately resistant, six (6) were moderately susceptible and one (susceptible check) was in susceptible category. Grouping of different lines/varieties under same cluster shows their significantly similar response against BLB disease in corresponding environment. Among the studied NILs, only one line showed polymorphism for all five resistant genes, two lines had four; seven lines had three genes, seven lines showed di-genic while five lines showed mono-genic polymorphism. These resistant lines with multiple-genes for BLB resistance can be evolved as a new BLB resistant variety and also be utilized as donor parent in breeding programs for developing new cultivars with horizontal resistance against more than one target pathotypes and environments. Xa4 and xa13 were found to deliver significant resistance against the local pathotypes in studied germplasm and NILs.
Highlights
Rice is one of the most important staple food of over half of the world’s population and about 90% of the world rice is grown and consumed in Asian continent [1]
Thirty-one (31) lines were categorized under resistant cluster, twenty-eight (28) were moderately resistant, six (6) were moderately susceptible and one was in susceptible category
Disease scoring was done by following the Standard Evaluation System (SES) of Rice developed by International Rice Research Institute (IRRI), Philippines
Summary
Rice is one of the most important staple food of over half of the world’s population and about 90% of the world rice is grown and consumed in Asian continent [1]. Bacterial leaf blight (BLB) disease is highly threatening all over the rice world. This disease is caused by rod-shaped bacterium Xanthomonas oryzae pv. Management of many improved and high yielding varieties with high nitrogen levels and close spacing expose the crop defenseless against the disease [5] This disease is the most devastating and serious threat to rice production. High spread of disease in favorable conditions make BLB more difficult to manage through conventional control methods such as chemical sprays. To combat this disease, innate genetic resistance of the plant plays vital role along with being environmentally friendly and economical. In the case of BLB resistance, cultivated rice and the wild relatives have been identified with 35 BLB resistance genes [6] [8] [9]
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