Improvement of bacterial blight resistance of the high yielding, fine-grain, rice variety, Gangavati sona through marker-assisted backcross breeding.

Gangavati sona (GS) is a high-yielding, fine-grain rice variety widely grown in the Tungabhadra command area in Karnataka, India; however, it is susceptible to bacterial blight (BB). Therefore, the present study was conducted to improve the GS variety for BB resistance. Three BB-resistant genes (xa5, xa13, and Xa21) were introgressed into the genetic background of susceptible cultivar GS through marker-assisted backcrossing (MABB) by using Improved samba Mahsuri (ISM), a popular, high-yielding, bacterial blight resistant rice variety as a donor parent. Foreground selection was carried out using gene-specific markers, viz., xa5FM (xa5), xa13prom (xa13), and pTA248 (Xa21), while background selection was carried out using well-distributed 64 polymorphic microsatellite markers. The true heterozygote F1 was used as the male parent for backcrossing with GS to obtain BC1F1. The process was repeated in BC1F1 generation, and a BC2F1 plant (IGS-5-11-5) possessing all three target genes along with maximum recurrent parent genome (RPG) recovery (86.7%) was selfed to obtain BC2F2s. At BC2F2, a single triple gene homozygote plant (IGS-5-11-5-33) with 92.6% RPG recovery was identified and advanced to BC2F5 by a pedigree method. At BC2F5, the seven best entries were selected, possessing all three resistance genes with high resistance levels against bacterial blight, yield level, and grain quality features equivalent to better than GS. The improved versions of GS will immensely benefit the farmers whose fields are endemic to BB.

Prediction of heterosis in rice based on divergence of morphological and molecular markers.

Identifying the best performing hybrid without a field test was essential to save resources and time. In this study, the genetic divergence was estimated using morphological and expressed sequence tag (EST)-derived simple sequence repeats (SSR) markers. Cluster analysis showed that APMS6A and RPHR 1005 belong to groups I and II, respectively, and the hybrid combination recorded the highest mean grain yield of 32.25 g among generated 40 F1s with standard heterosis of 8.4% over hybrid check, KRH2. The coefficient of marker polymorphism (CMP) value was calculated based on EST-SSRmarkers; it ranged from 0.40 to 0.80, and a higher CMP value of 0.80 was obtained for the parental combination APMS6A × RPHR1005. We predicted heterosis for 40 F1s based on correlation between CMP and standard heterosis in different traits with standard varietal and hybrid checks indicating positive correlation and significant value for grain yield per plant (r = 0.58**),productivity per day (r = 0.54**), productive tillers (r = 0.34*) and panicle weight (r = 0.42**). This study revealed that the relationship of molecular marker heterozygosity, along with the combining ability, high mean value of different traits,grouping of parental lines based on morphological and molecular characterization is helpful to identify heterotic patterns in rice.