Abstract
Bacterial blight, blast, and sheath blight are the commonest diseases causing substantial yield loss in rice around the world. Stacking of broad-spectrum resistance genes/QTLs into popular cultivars is becoming a major objective of any disease resistance breeding program. The varieties ASD 16 and ADT 43 are the two popular, high yielding, and widely grown rice cultivars of South India, which are susceptible to bacterial blight (BB), blast, and sheath blight diseases. The present study was carried out to improve the cultivars (ASD 16 and ADT 43) through introgression of bacterial blight (xa5, xa13, and Xa21), blast (Pi54), and sheath blight (qSBR7-1, qSBR11-1, and qSBR11-2) resistance genes/QTLs by MABB (marker-assisted backcross breeding). IRBB60 (xa5, xa13, and Xa21) and Tetep (Pi54; qSBR7-1, qSBR11-1, and qSBR11-2) were used as donors to introgress BB, blast, and sheath blight resistance into the recurrent parents (ASD 16 and ADT 43). Homozygous (BC3F3 generation), three-gene bacterial blight pyramided (xa5 + xa13 + Xa21) lines were developed, and these lines were crossed with Tetep to combine blast (Pi54) and sheath blight (qSBR7-1, qSBR11-1, and qSBR11-2) resistance. In BC3F3 generation, the improved pyramided lines carrying a total of seven genes/QTLs (xa5 + xa13 + Xa21 + Pi54 + qSBR7-1 + qSBR11-1 + qSBR11-2) were selected through molecular and phenotypic assay, and these were evaluated for resistance against bacterial blight, blast, and sheath blight pathogens under greenhouse conditions. We have selected nine lines in ASD 16 background and 15 lines in ADT 43 background, exhibiting a high degree of resistance to BB, blast, and sheath blight diseases and also possessing phenotypes of recurrent parents. The improved pyramided lines are expected to be used as improved varieties or used as a potential donor in breeding programs. The present study successfully introgressed Pi54, and qSBR QTLs (qSBR7-1, qSBR11-1, and qSBR11-2) from Tetep and major effective BB-resistant genes (xa5, xa13, and Xa21) from IRBB60 into the commercial varieties for durable resistance to multiple diseases.
Highlights
Rice (Oryza sativa L.) is considered a major staple food crop for billions of population across the globe, and it provides 23% of calories shared by different food crops (Sharma et al, 2012)
We have found that 9/134 plants in ASD 16 background and 13/150 plants in ADT 43 background were heterozygous for xa5, xa13, and Xa21, and these plants were screened with polymorphic SSR markers to assess the recovery of RPG
In BC3F1, we have found that 11/92 in ASD 16 background and 17/110 in ADT 43 background were shown to be triple heterozygous, and background assay indicates that three plants with RPG recovery ranged from 93.85 to 94.96% in ASD 16 combination, and two plants with a recovery of 94.26% and 94.04% were observed in ADT 43 combination (Supplementary Table S2)
Summary
Rice (Oryza sativa L.) is considered a major staple food crop for billions of population across the globe, and it provides 23% of calories shared by different food crops (Sharma et al, 2012). Exponential growth of the world population demands an increase in rice production by 26% to fulfill calorie requirements (Khush, 2013). The yield potential is frequently threatened by various biotic stresses, mostly fungi, and bacteria. To address these problems and to increase production, developing cultivars with durable resistance is a prerequisite. The host-plant resistance can be ideally improved through pyramiding of major R-genes/QTLs for multiple diseases and biotic stress factors
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