Performance of backcrosses involving transgressant doubled haploid lines in rice under contrasting moisture regimes: Yield components and marker heterozygosity

Improvement of grain yield in the rainfed lowland rice (Oryza sativa L.) ecosystem is important because that ecosystem covers a considerable area. The objectives of this study were first to find relationship(s) among grain yield and its components, second to assess the influence of root morphological characters on grain yield, and finally to find the relationship of molecular marker heterozygosity with heterosis-performance of yield related characters in rainfed lowland rice. Nine backcrosses involving transgressants for maximum root length in rice from a doubled haploid mapping population of IR64/Azucena along with parents were evaluated simultaneously for grain yield and related characters as well as root traits under contrasting moisture regimes. Grain yield showed maximum reduction under severe moisture stress conditions. Significant negative correlation between drought tolerance index and grain yield was observed in the well-watered conditions only. Multiple linear regression analysis revealed total dry weight (root + shoot dry weight) as the most significant variable under well-watered conditions because it could explain as much as 30% of variability in grain yield, followed by root number. Under severe stress conditions, root dry weight explained 20% of variability in grain yield. The relationships between yield and root related characters were determined. General heterozygosity, based on molecular marker data, was found to be correlated with hybrid performance and heterosis of yield related characters. Among the nine backcrosses, P331 x IR64 and P124 x IR64 were selected to map quantitative trait loci for root morphological characters and grain yield.