TERMINAL HEAT STRESS DIFFERENTIALLY MODULATES ROOT ARCHITECTURE, CARBOHYDRATE STATUS AND NODULATION IN LENTIL (LENS CULINARIS MEDIK.): IMPLICATIONS FOR IDENTIFYING HEAT-RESILIENT GENOTYPES

Abstract

Lentil is an important pulse crop which also provides biological nitrogen fixation advantage to cropping systems, but lentil sown late can suffer 36-59% loss in yield due to terminal heat stress, and India, the biggest producer and consumer of lentil, has to import about 1.2 million tonnes of lentil each year. Responses of lentil to shoot-level heat exposure have been investigated extensively, but root-level responses have not been investigated as much and there is a lack of systematic evaluation of root architecture, carbohydrate status, and nodulation across genotypes. A total of 28 lentil genotype were evaluated to determine their root, carbohydrate and nodulation responses under control, mid-late and late sowing to increase the amount of heat stress at the end of the season. Delayed sowing caused a drastic reduction in root volume (81.5%), root diameter (70.0%) and nodule number (72.3%), and moderate reduction in carbohydrate content (13.7%) with an increase in root length, suggesting a compensatory elongation response, root surface area was fairly stable. There was significant variation in each genotype for each of the traits, indicating different heat adaptation strategies. Root volume, diameter and nodule number were found to be correlated and grouped together as a "root vigor – nodulation" complex (PC1 31.2%) against which root elongation was opposed, and with surface area and carbohydrate content as a separate complex (PC2 23.9%), accounting for 55.1% of the variance. Nodule number was the most important direct factor in the path analysis of root biomass (0.49), mainly through root volume which is the most useful indirect selection criterion for breeding heat-tolerant lentil cultivars.