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Phenotypic and genotypic assessment of elite rice varieties for brown plant hopper (Nilaparvata lugens Stål.) resistance

Popular rice varieties from India which exhibited field resistance against Brown Plant Hopper attack were selected to validate their resistance reaction. Genotyping using twenty-four gene-specific markers for BPH resistance was carried out. Besides this, phenotyping of morpho-economic traits along with resistance reaction was performed. Stepwise regression of phenotypic data showed that the traits viz. trichome number, leaf area and leaf number per tiller were significantly correlated to BPH damage score, while the traits, grains per panicle, tiller number, plant height and leaf number per plant contributed significantly towards seed yield. It was observed that there was a positive association between leaf area and BPH damage while trichome number was negatively associated, causing decreasing value in damage score. In the case of yield, except leaf number per plant, others traits showed a positive association. Further, PCA biplot analysis results confirmed the findings. Phenotypically, the rice variety Hasanta exhibited the highest BPH resistance followed by Jyotirmayee, Mahanadi, Konark and Pratap. Out of the twenty-four gene-specific markers, six markers exhibited polymorphism and RM247 showed the highest polymorphic information content (PIC) value. Cluster analysis of the varieties based on the marker data placed the variety Hasanta in a separate cluster, confirming its distinctness. Genotyping confirmed the genetic nature of BPH resistance in Hasanta variety. The cluster 2.2a included the highest number of varieties based on genetic similarity although it comprised of resistant, moderately resistant and susceptible types. This finding indicated that phenotypic variation within genotypic similar groups might be due to environment or different sources of origin. Hence, this phenotypic and genotypic variation among the genotypes would be useful for selecting elite and potential BPH-resistant donors in a crop improvement program

Pyramiding Submergence Tolerance and Three Bacterial Blight Resistance Genes in Popular Rice Variety Hasanta through Marker-Assisted Backcross Breeding

Flash flooding (FF) along with bacterial blight (BB) outbreak are very destructive for rice production in the rainfed shallow-lowland (RSL) ecosystem. The presence of dynamic Xoo races with varying levels of genetic diversity and virulence renders their management extremely challenging under RSL. In this context, the marker-assisted improvement of plant resistance/tolerance has been proven as one of the most promising strategies towards the development of sustainable cultivars. The present study demonstrates the marker-assisted introgression of the submergence tolerant (Sub1) and three bacterial blight resistant genes (Xa21 + xa13 + xa5) into the genetic background of Hasanta, a long duration popular rice variety in the eastern coastal region of India. The rice genotypes, Swarna Sub1 (carrying Sub1) and IRBB66 (carrying Xa21 + xa13 + Xa7 + xa5 + Xa4) had maximum genetic similarity (0.84 and 0.73, respectively) with Hasanta; recurrent parent (RP) was used as donor. The forward analysis of target genes in F1s, IC1F1s and backcross (BC) generations was performed by linked/genic markers (Sub1bc2; pTA248, xa13prom and RM122), whereas background recovery of RP in each BC and segregating generations was performed utilizing 108 hypervariable SSR markers. Intervened speed breeding (SB) strategy and intensive phenotyping could lead the development of near isogenic lines (NILs) as to the RP in all basic traits. The performance of the near isogenic lines (NILs, BC2F3 and BC2F4), HS 232-411-391-756-37, HS 232-411-391-809-8, HS 232-411-391-756-18, HS 110-224-197-10-36, HS 232-411-391-809-81, HS 110-224-197-10-41 and HS 232-411-391-809-63 establishes the utility of marker-assisted backcross-breeding (MAB) and SB in accelerated trait introgression. The introgressed lines carrying Sub1 + Xa21 + xa13 + xa5 showed 76% to 91% survival under 14 days of submergence and durable BB resistance (percent disease index-PDI of 2.68 ± 0.26 to 6.22 ± 1.08 and lesion length, LL of 1.29 ± 0.12 to 4.2 ± 0.64 cm). Physiological analysis revealed that improved NILs, carrying Sub1 gene conquered adaptive physiological modulations, had reduced the consumption of soluble sugar and the degradation of total chlorophyll contents (TCC), and an enhanced level of Alcohol Dehydrogenase activity (ADH) and proline accumulation in all submergence regimes. The pyramided lines attained complete product profile of RP, that will contribute to sustainable rice production under RSL, particularly in the coastal region that has substantial acreage under the variety Hasanta