Dolichos bean is one of the ancient grain legumes grown in India for fresh beans for use as a vegetable and for dry grains as split dhal for use in various food preparations (
Ramesh and Byregowda, 2016). It serves as an important source of protein to many people who depend on vegetarian diets. It is predominantly grown in rain-fed eco-systems in southern Karnataka and adjoining districts of Tamil Nadu andhra Pradesh and Maharashtra both as inter crop and pure crop (
Ramesh and Byregowda, 2016).
Despite its multiple uses, dolichos bean is an ‘underutilized’ crop as evidenced by limited area planted to the crop, scale of consumption and efforts for its genetic improvement (
Ramesh and Byregowda, 2016). Enhancement of its economic value through the development of widely adapted and stable high yielding varieties is expected to offer competitive edge to dolichos bean to enable its popularity and wider cultivation (
Ramesh and Byregowda, 2016). As a result of shifts in rainfall pattern driven by climate change, the crop frequently experience moisture stress (MS) at pod filling and grain development stages, referred to as terminal MS (TMS). TMS significantly reduces grain yield in dolichos bean (
Ramesh and Byregowda, 2016). Sustainable production of dolichos bean requires (among others) identification/ development and use of TMS tolerant varieties. Breeding dolichos bean for TMS tolerance is still in infancy. Crop breeding for TMS has been less effective. This is because, TMS tolerance is a complex quantitative trait with confounding effects of high temperature and soil physico-chemical factors (
Blum, 2011).
Three approaches have been used to breed crop plants for tolerance to TMS (
Mitra, 2001). In the first approach, direct selection for yield under moisture stress free (MSF) conditions is practiced. The basic axiom of this approach is that genotypes that perform well MSF condition do so under MS as well (
Blum, 2011). Most often, this axiom is not necessarily true. In the second approach, direct selection for high yield under MS is practiced. Due to significant genotype × MS interaction coupled with low heritability, direct selection for yield potential under MS has been less effective resulting in low yield and hence, progress of breeding for resulting in low yield and hence, progress of breeding for tolerance to TMS is rather slow (
Mitra, 2001). In third approach, the ability of high yielding genotypes to tolerate TMS is enhanced by transferring genes controlling morphological, physiological and biochemical traits contributing to tolerance to TMS. Even this approach proved less effective due to inadequate understanding of genetic basis of these traits contributing to TMS tolerance (
Mitra, 2001). Considering the drawbacks of the three approaches, an alternative one which is the combination of the first two is suggested. In the alternative breeding approach, direct selection for high yield under MSF and stability of yield (with minimal reduction in yield) under MS is practiced (
Mitra, 2001;
Bennani et al., 2017). This alternative approach is attempted in the present study.
Detection and quantification of genetic variability within working germplasm/released varieties/available segregating populations for responses to TMS is not only a prerequisite, but also a short-term strategy for identification of TMS tolerant dolichos bean genotypes for use as varieties to cater to immediate needs of the farmers. Development/identification of appropriate indices is essential for quantification of responses of the experimental genotypes and identification of TMS tolerant ones for use as cultivars. Indices such as stress tolerance index (STI)
(Fisher and Maurer, 1978), mean productivity (MP) (
Rosielle and Hamblin, 1981), geometric mean productivity (GMP) and hormonic mean productivity (HMP) (
Fernandez, 1992), yield index (YI) (
Gavuzzi, 1997), drought susceptibility index (DSI) (
Lan, 1998), modified STI (K1STI and K2STI) (
Farshadfar and Sutka, 2002), abiotic tolerance index (ATI) and stress non-stress production index (SNPI)
(Moosavi et al., 2008) have been developed and frequently used in crop plants for quantification and selection of genotypes for tolerance to TMS. All these proposed indices are based on the extent of reduction in yield under MS condition relative to that under MSF condition. Identification of indices that enable empirical selection of genotypes with high yield under MSF conditions and acceptable stability of yield under MS conditions is the key (among others) for enhancing the progress in breeding for tolerance to TMS in any crop
(Bennani et al., 2017) with no exception of dolichos bean.
The objectives of the present investigation were to (1) identify indices that most significantly correlated with seed yield under both MSF and TMS conditions and (2) identify TMS tolerant genotypes using the most significantly correlated indices.