Drought resistance in spring wheat cultivars. III.* Yield associations with morpho-physiological traits

This paper describes associations between yield performance under drought and morpho-physiological traits, determined both under drought and non-drought conditions, for a large set of diverse cultivars of bread wheat (Triticum aestivum L.), durum wheat (T. turgidum L.), triticale (X Tritosecale Wittmack) and barley (Hordeum vulgare L). Performance under drought was considered in terms of grain yield and drought susceptibility, the latter being proportional to the decrease in yield relative to yield without drought. Species effects are considered, but greatest attention is paid to associations amongst bread wheat cultivars (n = 34), based on phenotypic and genotypic correlations, multiple linear regression and principal components analysis. Under drought, which reduced yield on average 60%, greater yield was most closely associated with greater total dry weight at maturity. Variation in traits associated with plant water relations had only a minor influence. The best prediction of yield under drought, from traits measured in the absence of drought (non-drought traits), was given by a linear model containing total dry weight, kernel weight and leaf waxiness, all with positive coefficients. Drought susceptibility, as defined, was unrelated to plant water relations under drought, but was related to various non-drought traits. It increased with increased non-drought yield, harvest index, kernels per sq metre, kernels per spike and leaf water potential, and with decreased plant height and waxiness. One part of these associations with drought susceptibility appeared to be related to variation in height, probably arising from the action of the Norin 10 dwarfing genes; part, however, was independent of height. The relationships suggested that direct selection for increased yield in the absence of drought, or selection via most of the non-drought traits, increased drought susceptibility and, depending on drought level, may increase or decrease yield under drought. No trait had clearly desirable effects on yield both in the absence of drought and drought susceptibility; total dry weight appeared to have the least undesirable effect on susceptibility. ______________________ *Part 11, Aust. J. Agric. Res. 30: 801 (1979).