Efficiency of physiological trait-based and empirical selection approaches for drought tolerance in groundnut

Drought is the major abiotic constraint affecting groundnut productivity and quality worldwide. Most breeding programmes in groundnut follow an empirical approach to drought resistance breeding, largely based on kernel yield and traits of local adaptation, resulting in slow progress. Recent advances in the use of easily measurable surrogates for complex physiological traits associated with drought tolerance encouraged breeders to integrate these in their selection schemes. However, there has been no direct comparison of the relative efficiency of a physiological trait-based selection approach (Tr) vis-à-vis an empirical approach (E) to ascertain the benefits of the former. The genetic material used in the present study originated from three common crosses and one institute-specific cross from four collaborating institutes in India (total seven crosses). Each institute contributed six genotypes and each followed both the Tr and E selection approaches in each cross. The field trial of all selections, consisting of 192 genotypes (96 each Tr and E selections), was grown in 2000/2001 in a 4 x 48 alpha design in 12 season x location environments in India. The selection efficiency of Tr relative to E, RE_Tr, was estimated using the genetic concept of response to selection. Based on all the 12 environments, the two selection methods performed more or less similarly (RE_Tr, = 1.045). When the 12 environments were grouped into rainy season and post-rainy season, the relative response to selection in Tr method was higher in the rainy than in the post-rainy season (RE_Tr = 1.220 vs 0.657) due to a higher genetic variance, lower G x E, and high h². When the 12 environments were classified into four clusters based on plant extractable soil-water availability, the selection method Tr was superior to E in three of the four clusters (RE_Tr = 1.495, 0.612, 1.308, and 1.144) due to an increase in genetic variance and h² under Tr in clustered environments. Although the crosses exhibited significant differences for kernel yield, the two methods of selection did not interact significantly with crosses. Both methods contributed more or less equally to the 10 highest-yielding selections (six for E and four for Tr). The six E selections had a higher kernel yield, higher transpiration (T), and nearly equal transpiration efficiency (TE) and harvest index (HI) relative to four Tr selections. The yield advantage in E selections came largely from greater T, which would likely not be an advantage in water-deficient environments. From the results of these multi-environment studies, it is evident that Tr method did not show a consistent superiority over E method of drought resistance breeding in producing a higher kernel yield in groundnut. Nonetheless, the integration of physiological traits (or their surrogates) in the selection scheme would be advantageous in selecting genotypes which are more efficient water utilisers or partitioners of photosynthates into economic yield. New biotechnological tools are being explored to increase efficiency of physiological trait-based drought resistance breeding in groundnut.