Tagging QTLs for maximum root length in rainfed lowland rice (Oryza sativa L.) using molecular markers.

A number of morphological, physiological and phenological traits are known to improve the performance of rice challenged by drought. Root morphological traits and stress-induced response form important components of drought tolerance. Enhancing grain yield remains the principal objective of most breeding programs. Interaction between primary traits poses a formidable challenge while dealing with grain yield under stress. The evaluation of root morphology at three different growth stages and grain yield along with related characteristics under contrasting moisture regimes was made using nine backcrosses along with their parent and standard checks. The backcrosses invoved transgressant double haploid lines derived from IR64 and Azucena with IR64. Marked genotypic differences were observed for all root morphology as well as grain yield related characteristics across the sampling dates as revealed by individual and combined ANOVA. Among the nine backcrosses studied in this experiment, the BC1F2 population of P124 x IR64 were evaluated for forwarding based on their performance with respect to maximum root length and grain yield under both well-watered and low-moisture stress conditions. Sixty-nine plants - ten percent of the backcross population - were selectively genotyped using RAPD primers. Under well-watered conditions two RAPD markers showed strong linkage to QTLs for maximum root length evaluated under ww conditions. Two other markers could explain the considerable amount of variation in MRL under LMS. One of the markers identified under low-moisture stress conditions was also able to explain variability in maximum root length in the mean environment.