Effect of deficit irrigation on kernel yield, yield components and some physiological traits of different varieties of bread wheat and durum wheat

Currently, the most important selection criterion for drought tolerance in wheat breeding programs is to compare grain yields between wheat cultivars grown under normal and deficit irrigation conditions. Several reports indicate that wheat traits, such as grain yield, biomass and yield components are decreased when the crop encounters water stress (Mohseni and Akbari, 2012). Heritability for yield is low under drought conditions due to high interaction between genotype and environment or low genetic variation. For this reason, secondary characteristics such as physiological traits have been given particular attention for selection process by researchers. Leaf relative water content (LRWC), chlorophyll content, water use efficiency (WUE), proline and abscisic acid accumulation are of some physiological indices as a measure for selection of drought tolerant cultivars. LRWC is considered as a screening tool under drought condition. (Blum et al., 1981). LRWC is affected by osmotic pressure, water uptake and respiration rate and shows a high heritability under drought conditions. Crop chlorophyll (Chl) content decreases under drought conditions and plants with high Chl content are more tolerant to drought (Abdoli et al., 2013). In crops with high chlorophyll content, photosynthesis activity continues under drought conditions. Thus the experiment was conducted to investigate the effect of limited irrigation on some morphological and physiological traits of bread and durum wheat under Mashhad-Iran environmental conditions The study was conducted at experimental field of Ferdowsi university of Mashhad during 2011 and 2012 growing seasons in order to evaluate the effect of limited irrigation on yield and physiological characteristics of wheat. A split plot experiment based on randomized complete block design with three replications was performed. The main plots were assigned to irrigation levels including (I1)100, (I2)75, (I3)50 and (I4) 25 percent of evaporation from evaporation pan class A and the sub-plots consisted of wheat cultivars (three hexaploid cultivars (Pishgam, Alvand, Erum) and three durum cultivars (Behrang, Arya, Dena). Land preparation was done on late October according to farmers practice in the area. There were six 3m long rows spaced 20cm apart in each plot. The studied characteristics were yield component traits, flag leaf chlorophyll content, chlorophyll (Chl) a, and b contents and flag leaf relative water content (LRWC). The results of analysis of variance showed that there was significant difference between cultivars in terms of grain yield. Also, grain yield was significantly affected by irrigation levels but was not affected by interaction between the treatments. The highest (723 kg/m2) and lowest (677 kg/m2) grain yields were produced by Pishgam and Alvand cultivars respectively. The highest (52%) and lowest (32%) harvest index were observed for Dena and Erum cultivars, respectively. There was no significant difference between irrigation levels for harvest index. There was no significant difference between cultivars for chlorophyll content There was a significant difference between cultivars for chlorophyll a content. The highest chlorophyll a content (2.49 mg/g fresh weight) was observed for Dena cultivar. There was significant difference between irrigation levels for chlorophyll a and b contents. Chlorophyll content was significantly affected by irrigation level and chlorophyll a and b concentrations were decreased by water deficit. There was no significant difference under normal irrigation levels between chlorophyll content index and the Chl a, and b concentrations. LRWC was different with different cultivars and was affected by irrigation levels. The highest and lowest LRWC were obtained with Pishgam and Alvand cultivars, respectively. There was no significant difference between the other cultivars for LRWC . The highest grain yield was obtained from Pishgam and Alvand cultivars. The former and the latter gave the highest yield because of higher 1000-grain weight and higher numbers of grain per spike, respectively. Harvest index of all the wheat cultivars remained stable and was not affected by water stress. Water stress reduced LRWC, chlorophyll index content and chlorophyll a and b concentrations. The reduced chlorophyll content led to diminished production of photosynthates, resulting in decreased grain yield and biomass in the all cultivars. Since selection based on grain yield is not useful because of its low heritability, LRWC can be used as the selection criterion for cultivars with high yield performance under water deficit conditions.