Introduction of new indices to identify relative drought tolerance and resistance in wheat genotypes

Three new indices namely: abiotic-stress tolerance index (ATI) (Abiotic-stress Tolerance Index)†, stress susceptibility percentage index (SSPI) (Stress Susceptibility Percentage Index) and stress non-stress production index (SNPI) were introduced to identify relatively tolerant (through ATI and SSPI) and resistant (through SNPI) genotypes under nonirrigated and irrigated conditions. Sixteen bread wheat genotypes (in 2004, under a moderate stress with SI = 0.31) and twenty durum wheat genotypes (2004 and 2005 under a severe stress with SI = 0.57) were studied in field experiments under non-irrigated and irrigated conditions. Yield changes in non-irrigated and irrigated conditions for different genotypes, the primary selection of genotypes for relative drought tolerance or resistance and a comparison between new indices and previous ones were studied. In this paper, “relative tolerance and resistance” phrases are used instead of “tolerance and resistance” because we believe that, generally, there are no complete tolerance and resistance to abioticstress. ATI and SSPI exhibited a positive significant simple correlation with TOL, Yp and SSI, but their correlations with RDI were significantly negative. ATI and SSPI differentiated between relative tolerant and intolerant genotypes better than TOL and SSI in some cases and were considered as a favorite index for the selection of relatively tolerant genotypes. ATI and SSPI are powerful to select extreme tolerant genotypes with yield stability and may be can use of them as parents in conformation to a QTL population for yield stability in two irrigated and non-irrigated conditions, because, both of them are related to relatively yield stability and may be state that a genotype with suitable yield stability carries drought tolerance or other related trait genes. SNPI had a positive correlation with yield changes in both non-irrigated and irrigated conditions and negative correlation with SSI and TOL, therefore, to select a genotype with appropriate, high and stable yield in both stress and non-stress conditions for commercial aims, it is suggested to use SNPI as a desirable index because this index supports stable and high yield in both conditions (especially in non-irrigated condition) simultaneously.