Genetic variation of root and shoot traits at early stage in a lentil (Lens culinaris Medik) recombinant inbred lines (RILs) population under drought: towards Quantitative Trait Loci (QTL) mapping

Well-developed roots and vigorous shoots at early-seedling stage are important for drought tolerance in lentil (Lens culinaris Medik). 135 RILs derived from a cross between two contrasting parents ILL6002 and ILL5888 (obtained from JF Muehlbauer, Washington State University) is under phenotyping and genotyping in order to assess the genetic control behind root and shoot traits at early growth stage. The phenotyping was carried out in a plastic pot experiment under well-watered and progressive drought-stressed treatments. ILL6002 is a vigorous line with a well developed root system showing drought tolerance, while ILL5888 has a less developed root system and vegetative biomass showing drought sensitivity. The analysis of variance shows significant differences between the RILs for all the studied traits. Significant correlations with drought tolerance were observed for dry root weight (0,616), root surface area (0,516), lateral root number (0,476), root-shoot ratio (0,377) and chlorophyll content (0,452) and dry shoot weight (0,282). The frequency distributions of dry root weight, lateral root number, taproot length, mean taproot diameter, root surface area, dry shoot weight, shoot length at 12 and 22 days after sowing, seedling vigour, chlorophyll content, root-shoot ratio and drought score in the RILs were quantitative, continuous and normally distributed. Thus, suggesting polygenic control of these traits involving probably many QTLs of variable effects. The existing genetic map is being saturated by Amplified Fragment Length Polymorphism and microsatellite markers in order to enhance the resolution of QTL mapping.