English

Abstract

The Bacterial Leaf Blight (BLB) disease of rice caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the main reasons limiting production of rice in Asia ensuing to an average of 20 to 30% and in some Asian countries, up to 50% rice yield losses .The disease, when occurs in severe condition on susceptible cultivars, causes 74 to 81% yield losses (Srinivasan and Gnanamanickam, 2005). It was reported that yield losses can be 100% in Basmati rice at tillering stage (Mannan et al., 2009). Cultural practices, chemical control or resistant varieties are optional strategies for the control of plant diseases. The chemical control of BLB is impractical in the monsoon climatic conditions of Asia (Agrawal et al., 2005). Furthermore, no effective bactericide is commercially available for disease control. Therefore, the preferred strategy for disease management is through varietal resistance (Naveed et al., 2010). The manipulation of host resistance has been shown to be the only and most reliable method to manage this disease. Globally, to date, 39 Xa genes (28 dominant and 11 recessive) conferring resistance against Xoo have been identified (Chen et al., 2011; Zhang et al., 2014). These identified genes were evaluated in different countries against their indigenous Xoo populations to deploy in local germplasm for BLB resistance. The response of 23 lines like 10 NILs and 13 pyramids was evaluated against BLB under field conditions in Vietnam. The resistance gene xa13 and Xa14 were susceptible, Xa4 and xa5 were moderately susceptible and the rest were moderately resistant to BLB. Among the pyramids, Xa4+xa5+xa13+Xa21, Xa4+Xa7+Xa21 and xa5+Xa7+xa13 had short lesion length and low diseased leaf area (Loan et al., 2006). Three gene pyramid (xa5+xa13+Xa21) in variety Sawarna was transferred to Jalmagna, a popular deep-water variety in India, which exhibited a high level of resistance against BLB (Pradhan et al., 2015). However, the durability of resistance depends upon the prevalence of pathogen races in time and space. A lot of research has been done on the evaluation of rice genotype (Khan et al., 2009), virulence reaction of local Xoo isolates (Mannan et al., 2009), molecular screening of local germplasm against a specific R gene (Abbasi et al., 2011) and evaluation of resistance genes in rice against local isolates of Xoo (Khan et al., 2012) in Pakistan. But for the development of durable resistant cultivar, it is of prime importance to screen all available resistant genes either single or in combination against all prevailing 29 pathotypes of Xoo Pak. J. Agri. Sci., Vol. 53(2), 365-370; 2016 ISSN (Print) 0552-9034, ISSN (Online) 2076-0906 DOI: 10.21162/PAKJAS/16.5357 http://www.pakjas.com.pk