Marker assisted backcross breeding for submergence tolerance in rice variety Rajendra Sweta
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Date
2019-02-02
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Department of Plant Breeding and Genetics, BAU, Sabour
Abstract
Submergence stress regularly affects rice crop in major parts of eastern India comprising Odisha, West Bengal, Bihar, Assam, Chhattisgarh and eastern Uttar Pradesh. Out of 42 biotic and abiotic stresses that prevail in rainfed lowland rice areas of eastern India, submergence stress is the third most important limitation to rice production. A major QTL mapped on chromosome 9, designated as sub1, has provided the scope to apply marker assisted backcrossing (MABC) to develop submergence tolerant varieties suitable to be grown in these regions. Developing rice cultivars with tolerance of submergence and with agronomic and quality traits acceptable to farmers is a feasible approach to address this problem. In the present study, BC2F1 generation was developed between a submergence tolerant donor, Swarna-Sub1and the widely grown recurrent parent, Rajendra Sweta. A parental polymorphism survey between these two parents revealed 46 polymorphic SSR loci covering all the chromosomes of rice genome. Foreground selection was done in each generation for the confirmation of Sub1 QTL. Molecular markers that were tightly linked to Sub1, flanking Sub1 and unlinked to Sub1 were used to apply foreground, recombinant and background selection, respectively, in BC2F1 generation. Out of 91 plants, 50 plants were found positive in foreground selection using Indel primer Sub1bc2. Recombinant selection was done on these 50 heterozygous plants with RM219. Out of these 50 individuals, five recombinants were selected namely, BC2F1-4,BC2F1-28,BC2F1-37,BC2F1-43 andBC2F1-79. Background selection was carried out on these five recombinants with 46 SSR markers. Recipient allele frequency was calculated for these five recombinants which ranged from 51.1% to 78.2%. In BC2F1 generation, maximum recipient parent recovery obtained was 78.2% for individual BC2F1-79. Screening for submergence tolerance revealed that the recombinants were able to survive complete submergence for 14 days and were also able to recover faster upon de-submergence. Higher ADH enzyme activity was observed in donor as well as recombinants during submergence. Similarly, higher concentration of carbohydrate before submergence and its slower depletion during submergence was observed in all the recombinants. Chlorophyll content was found greater in the recombinants than the recipient parent Rajendra Sweta.Morphological observations (days to flowering, plant height, tiller number, flag leaf length, panicle length, number of grains per panicle and grain yield per plant) under stress condition revealed that for all the traits Sub1’s were similar to or better than Rajendra Sweta. The newly improved rice line, BC2F1-79 containing Sub1and showing highest recovery may further be utilized in backcross breeding program to improve its recovery percentage and the similar strategy can be followed to introgress other QTLs for biotic and abiotic resistance into the high yielding varieties.