Abstract
Bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo) has now become one of major rice diseases. During recent years, its occurrence has increased in Pakistan, particularly in ‘Kallar tract’ which is well-known for quality rice cultivation. Development of new resistant varieties by utilizing the available resistant gene-pool is most reliable breeding technique for the plant breeders. The present study was conducted to explore the genetic resources regarding presence and absence of BLB resistance genes Xa4 , xa5 and Xa21 through DNA marker technology. Effectiveness of Xa21 followed by xa5 and Xa7 genes has been reported to confer more resistance level for BLB in traditional rice belt of Pakistan. For this purpose, eighty (80) rice genotypes comprising of diverse origin including three isogenic lines viz., IRBB4 (carrying Xa4 ), IRBB5 (carrying xa5 ) and IRBB21 (carrying Xa21 ) as positive resistant gene checks and IR24 (carrying none of these) as negative gene check were genotyped. DNA fingerprinting results indicated the presence of Xa4 gene in 41 entries, while 14 lines were positive for xa5 gene. Only one local line was carrying Xa21 gene along with Xa4 . Thus, the present study will not only be helpful for rice breeders to develop new rice varieties carrying disease resistant genes, but will also provide the donors to incorporate / pyramid disease resistant genes in popular rice varieties like Super Basmati and Basmati 515 which are susceptible to BLB disease. Keywords: Molecular screening, rice germplasm, Xa4, xa5 and Xa21 genes, bacterial leaf blight
Highlights
Millions of people in the world take rice as a staple food (Chakravarti et al, 2012; Deepti et al, 2013)
Amplification of marker MP1which is a sequence-tagged site (STS) marker linked to Xa4, revealed a 150 bp fragment specific for Xa4 mediated Bacterial leaf blight (BLB) resistance in near-isogenic lines (NILs) IRBB4, and a 120 bp DNA fragment that corresponds to a susceptible variety IR24 (Figure 1)
This study indicates the presence of Xa4 gene in forty one (41) rice genotypes, xa5 in fourteen (14) genotypes, while Xa21 in only two (2) genotypes including NILs among all the studied eighty (80) genotypes
Summary
Millions of people in the world take rice as a staple food (Chakravarti et al, 2012; Deepti et al, 2013). The usage of rice is more than 90% in Asian countries, it is consumed and produced more in Asia. In Pakistan, rice is a major cash crop as well as staple food. It is cultivated on 6.82 million acres occupying about 11% of total cultivated area during 2014 to 2015 and produces 6.73 million metric tons of milled rice (Economic survey of Pak., 2015). Pakistan was ranked as third exporter of Basmati rice.
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