Effect of Terminal Water Stress on Grain Yield and Morpho-physiological Traits of Aegilops triuncialis Ecotypes

Drought stress is the most important and common environmental stress that annually bring huge damage to crops in the world and especially in Iran, which is considered as an arid and semi-arid country. Nowadays, most plants breeding plans for resistance against drought and preparing resistant species are to achieve favorable yield in arid environments and are based on recognizing morpho-physiological and biochemical traits and involved genes and transforming them to cultivars. There is a genetic diversity regarding resistance against aridity among Aegilops species that can be used to improve resistance against aridity in wheat during different stages of reproduction and plant growth. This investigation was performed in green house of Agricultural Faculty in University of Mohaghegh Ardabili on 2011 in order to survey the effects of aridity stress and study the traits related to resistance in eight ecotypes of Aegilops triuncialis (ecotypes of Maku, Marand, Hashtrud, Namin, Hurand, Karaj, Meshkin and Ahar). The experiment was performed in three replications as factorial and based on completely randomized design. Different stages of irrigation including full irrigation as control, cutting of irrigation from booting (T1), (zadoks stage 45) and from 50% spike emergence (T2) (zadoks stage 55) to maturity were considered as water stress levels. Studied morphological traits include plant height (cm), plant dry weight (g), peduncle length (cm), spike length (cm), number of grains in spike, weight of grains per spike (g), 100 grain weight (g), spike dry weigh (g), root length and root mass. Chlorophyll content was measured by SPAD-502 machine. In order to measure fluorescence content of chlorophyll, OSI 30 machine of ADC Bioscietific Company and to measure stomatal conductance leaf porometer (SC-1 model) were used. Data analysis was performed by SAS ver.9.1 software and cutting was done in case of significant interactive effect. Mean comparison was done by Lsmeans test at probability level of 5%. Water stress decreased all evaluated traits especially grain yield (89%). Water stress condition, by damaging photosynthesis system, reduced photochemical efficiency of PS II and chlorophyll index. Stomatal conductance rate reduced by 46% at booting stage and 55% at spike emergence and also decreased relative water content by 26% compared to normal circumstances. Although drought stress application in the experiment decreased grain yield in ecotypes compared to no stress conditions, some ecotypes like Hashtrud, Hurand and Maku could resist stress conditions and showed less grain yield decrease in comparison to the others. Ecotypes of Hashtrud, Marand, Meshkin could supply their necessary moisture from deep soil by increasing their root length. Ecotypes with higher ratio of Fv/Fm and less chlorophyll index decrease under stress condition could have less grain yield decrease. It seems that superiority of Hashtrud, Hurand and Maku ecotypes in stress conditions compared to other ecotypes could be due to these characteristics. Terminal drought results in reduced growth period, length, peduncle length, main panicle length and also reduced grain yield. Drought stress by damaging photosynthesis system and decreased photosynthesis and chlorophyll and limiting photosynthesis allocations of grains under stress condition decreases their weight and finally their yield.