Assessment of drought resistance in different bread wheat lines using agro-physiological traits and integrated selection index

Drought as one of the most important environmental stresses and limiting production of crops such as wheat, often leads to a significant decline in production. Identify and use specific physiological traits in breeding programs and also producing cultivars with characteristics consistent with drought conditions is one of the most important steps in drought stress studies. The aim of this study was to evaluate the diversity of bread wheat landraces in response to drought stress based on some agro-physiological traits (grain yield, gas exchange parameters, relative water content, chlorophyll and carotenoid contents) and also to exploring the possibility of selecting superior agro-physiological traits in identify drought tolerant genotypes using integrated selection index.
This experiment was conducted on 19 landraces of bread wheat in a randomized complete block design with three replications under normal and rainfed conditions in the Campus of Agriculture and Natural Resources, Razi University, Kermanshah, Iran during 2011-2012 cropping season. Sowing was done by hand at five row plots, 2 m length, and 0.20 m row spacing as 400 seeds per square meter density. Chemical fertilizers were not used during the research. The weeds control wad done by hand and using 2,4-D herbicide before stem elongation stage of wheat. Non-stressed plots were irrigated according to regional needs at heading, flowering and kernel filling stages. At full physiological maturity, two middle rows of each plot at both conditions were harvested to determine kernel yield per unit area.
The mean of grain yield in irrigated and rainfed conditions were 1651 and 1273 Kg/ha, respectively, means that drought stress reduced grain yield as much as 22.86% but it increased proline by 253%. The considerable variation was not observed among genotypes in both conditions for gas exchange traits, except stomatal conductance. All the gas exchange-related traits were reduced due to drought stress so that the stomatal conductance had the highest reduction by 45%. Genotypes number 4, 9, 18 and 11 were known as tolerant genotypes based on all studied traits using integrated selection index. In ranking method which calculated based on all studied traits under rainfed conditions, mean rank, standard deviation of ranks and rank sum parameters, genotypes number 5, 2, 15 and 18 with the lowest rank sum were identified as the most drought tolerant genotypes by consideration the rank of each genotypes for kernel yield under both conditions, the value of studied traits and the integrated selection index, while genotypes number 3, 9, 13 and 10 as the most sensitive. In examining the relationship between various physiological indicators of drought tolerance, grain yield under both conditions and integrated selection index, using Biplot, the PCA1 and PCA2 axes justifed 51.46 % of total variation.
Integrated selection index introduced genotypes 4 (WC-4530), 9 (WC-47381), 18 (WC-47636) and 11 (WC-4566) as the most drought tolerant. Principal component analysis showed that integrated selection index (ISI) had close relationship with chlorophyll a, chlorophyll b, carotenoid, leaf temperature, proline concentration, photosynthesis rate, stomatal conductance and grain yield under both conditions, therefore these traits were identified as superior traits for selecting drought tolerant genotypes using biplot graph.