Flooding is one of the major constraints for rice production in rainfed lowlands, especially in years and areas of high rainfall. Incorporating the Sub1 (Submergence1) gene into high yielding popular varieties has proven to be the most feasible approach to sustain rice production in submergence-prone areas. Introgression of this QTL into popular varieties has resulted in considerable improvement in yield after flooding. However, its impact under non-flooded conditions or years have not been thoroughly evaluated which is important for the farmers to accept and adopt any new version of their popular varieties. The present study was carried out to evaluate the effect of Sub1 on grain yield of rice in different genetic backgrounds, under non-submergence conditions, over years and locations. The study was carried out using head to head trials in farmer’s fields, which enable the farmers to more accurately compare the performance of Sub1 varieties with their recurrent parents under own management. The data generated from different head to head trials revealed that the grain yield of Sub1 varieties was either statistically similar or higher than their non-Sub1 counterparts under non-submergence conditions. Thus, Sub1 rice varieties show no instance of yield penalty of the introgressed gene.

BACKGROUNDNutrient deficiency in humans, especially in children and lactating women, is a major concern. Increasing the micronutrient concentration in staple crops like rice is one way to overcome this. The micronutrient content in rice, especially the iron (Fe) and zinc (Zn) content, is highly variable. The identification of rice genotypes in which there are naturally high Fe and Zn concentrations across environments is an important target towards the production of biofortified rice.RESULTSPhenotypic correlations between grain Fe and Zn content were positive and significant in all environments but a significant negative association was observed between grain yield and grain Fe and Zn. Promising breeding lines with higher Zn or Fe content, or both, were: IR 82475‐110‐2‐2‐1‐2 (Zn: 20.24–37.33 mg kg−1; Fe: 7.47–14.65 mg kg−1); IR 83294‐66‐2‐2‐3‐2 (Zn: 22–37–41.97 mg kg−1; Fe: 9.43–17.16); IR 83668‐35‐2‐2‐2 (Zn: 27.15–42.73 mg kg−1; Fe: 6.01–14.71); IR 68144‐2B‐2‐2‐3‐1‐166 (Zn: 23.53–40.30 mg kg−1; Fe: 10.53–17.80 mg kg−1) and RP Bio 5478‐185M7 (Zn: 22.60–40.07 mg kg−1; Fe: 7.64–14.73 mg kg−1). Among these, IR82475‐110‐2‐2‐1‐2 (Zn: 20.24–37.33 mg kg−1; Fe: 7.47–14.65 mg kg−1) is also high yielding with 3.75 t ha−1. Kelhrie Cha (Zn: 17.76–36.45 mg kg−1; Fe: 7.17–14.77 mg kg−1), Dzuluorhe (Zn: 17.48–39.68 mg kg−1; Fe: 7.89–19.90 mg kg−1), Nedu (Zn: 18.97–43.55 mg kg−1 Fe: 8.01–19.51 mg kg−1), Kuhusoi‐Ri‐Sareku (Zn: 17.37–44.14 mg kg−1; Fe: 8.99–14.30 mg kg−1) and Mima (Zn: 17.10–45.64 mg kg−1; Fe: 9.97–17.40 mg kg−1) were traditional donor genotypes that possessed both high grain Fe and high Zn content.CONCLUSIONSignificant genotype × location (G × L) effects were observed in all traits except Fe. Genetic variance was significant and was considerably larger than the variance of G × L for grain Zn and Fe content traits, except grain yield. The G × L × year variance component was significant in all cases. © 2020 Society of Chemical Industry

Flooding is one of the major constraints of rice production in the rainfed lowland rice ecosystem. To cope with the frequent flooding in the climate change regime, tolerant cultivars are urgently needed to protect the paddy crop from flash floods. With the help of molecular markers, a major QTL for submergence tolerance "Sub1" was introgressed into a rainfed lowland mega variety Ranjit of N.E. India, by backcrossing followed by two generations of selfing. In this modified marker-assisted backcrossing (MABC), a gene based marker Sub1BC 2 and 50051 SNPs were used for foreground and background selection, respectively, in backcrosses between a Sub1 donor, Swarna-Sub1 and the recipient variety, Ranjit. The recombinant selection was skipped and background selection was deferred to BC 2 F 2 generation. The size of the donor fragment was found to be 1.65Mb. The introgression of this small segment was possible due to large population and strict selection in segregating generations for the recurrent parent with the help of 62 DUS characters. Ranjit-Sub1, a selection in BC 2 F 2 generation, showed background recovery of 96.54% and submergence tolerance similar to the tolerant donor parent. Yield, yield-components and grain physico-chemical properties showed successful recovery of these traits in Ranjit-Sub1, with yield potential ranging from 6.5 to 7.0 t/ha, not significantly different from the recurrent parent, Ranjit. Therefore, Ranjit-Sub1 has been recommended for Zone III for submergence stress conditions in India. The study demonstrates a rapid and highly precise strategy adopted to introgress a major QTL by BC 2 F 2 generation into a modern rice variety using a modified MABC.

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