Diversity of root and shoot traits associated with drought tolerance in groundnut germplasm and advanced breeding materials

Abstract

Groundnut (Arachis hypogaea L.) genotypes (351) belonging to three different market types, i.e., Vulgaris (VUL), Fastigiata (FST) and Virginia (VIR) were analysed for yield and physiological traits, under field conditions during 2009 wet season. Most of the genotypes belonging to VIR exhibited high biomass, pod yield, SPAD - reading, leaf stomatal density, 100 - seed mass and, low specific leaf area (SLA) and UC. On the other hand, most of the genotypes belonging to VUL and FST exhibited high HI, shelling outturn and SLA. The UC was directly associated with SLA (r=0.53 * *) indicating that higher the SLA lower the drought tolerance. Based on variations in physiological parameters, 92 genotypes were selected and analysed in 3D concrete - blocks for various roots and shoot traits, after imposing water deficit stress, during 2010 dry season. Bi - plot analysis showed significant trait - by - trait and genotype - by - trait interactions between various roots and shoot parameters. For example, angle between line of vector of primary root length (PRL) and Fv/Fm ratio, leaf relative water content (RWC) and total biomass (TBIO) were acute indicating direct association between these traits. On the other hand, lines of vector of PRL and folding of leaves were in appositive direction indicating that these two traits are inversely associated. Also, length of vector was higher for the traits, i.e., PRL, SRL, R:S ratio, TBIO, RV, root weight density while moderate for RWC, Fv/Fm and SDRL. In addition, SLA was correlated with PRL (r= - 0.42 * *), secondary root length (SRL) (r= - 0.53 * *), secondary dense root length (SDRL) (r= - 0.72 * *) and root volume (RV) (r= - 0.58 * *). It is presumed that SLA along with desirable roots traits played crucial role in determining drought tolerance or otherwise. Further, based on PRL, genotypes were classified as high (>96.8 cm) and low (<76.4 cm) ranks, most of high rank genotypes exhibited low SLA, high TBIO, Fv/Fm and RWC, while most of the low rank genotypes were having high SLA, and rest all above mentioned traits were lower than high rank. In addition, some genotypes were identified with high TBIO, irrespective of PRL and SLA, but Fv/Fm and RWC in these were significantly lower than genotypes having low SLA and high biomass, indicating that these genotypes might be suitable for irrigated conditions. Genotype NRCG 12109 was identified having all desirable traits, and this could be ‘plant type’ for drought tolerance. This study offers valuable genetic material for use in breeding programmes to develop new cultivars for drought prone areas in semi - arid tropics, worldwide, and Fv/Fm could be used as screening tool for drought tolerance.