Effect of Drought Stress on Water Use Efficiency and Its Components in Several Genotypes and Cultivars of Foxtail Millet (Setaria italica L.)

IntroductionAccording to NASA reports about atmospheric earth conditions, in the 30 years later, 45 countries will face with severe droughts and Iran is in the fourth place in this list. Water shortage is one of the most important limiting factors of production that affects plants growth by changing physiological conditions. Using adapted plants is a proper strategy to deal with the effects of water shortage on the status of water restrictions. Foxtail millet is a C4 plant with good compatibility to dry areas and it has high water use efficiency. In medium stress partial stomata closure reduces transpiration more than photosynthesis in this plant and as a result, increase water use efficiency.
Materials and MethodsThis experiment was carried out as split-plot layout based on randomized complete blocks design with four replications at the Agricultural Research Station, University of Birjand in 2014-2015. The main factor was drought stress in three levels including 100, 75 and 50 percent of plant water requirement (no stress as control, moderate stress and severe stress, respectively) and the sub-factor was millet genotype in three levels (including Bastan, KFM5 and KFM20). At four leaf stage, 75 plants per square meter were maintained and applied stress. Water use efficiency, evapotranspiration efficiency, harvest index for seed and ear, economic and biological yield were measured at maturity. . Data were analyzed with the SAS software ver 9.1 and the means were compared with Tukey’s test.
Results and DiscussionThe results showed that water use efficiency (WUE) was significantly decreased with increasing the intensity of drought stress in all three genotypes but not evapotranspiration efficiency (ETE, ratio of total dry matter to water used). Bastan cultivar had higher water use efficiency in all stress levels and was more affected under moderate stress while it was less affected under severe stress (33 and 31 percent compared to the control, respectively). The evapotranspiration efficiency (ETE) was similar in all three genotypes and did not change under stress condition. The water use efficiency was different in two years but drought stress had a similar effect on its. The drought stress reduced seed yield through its impact on water use efficiency, harvest index and total dry matter within two years. The highest and lowest seed yield were observed in control (152 g m-2) and severe stress (171 g m-2), respectively. Significant genotypic variation was observed for WUE (ratio of grain yield to water used), and harvest index (HI, ratio of grain yield to total dry matter). Bastan cultivar had higher WUE than two other lines in well-watered (0.82 vs. 0.63 g kg−1) and drought (0.56 vs. 0.42 g kg−1) field conditions, due mainly to higher HI in well-watered (41.04 vs. 36.01 percent) and drought (26.2 vs.25.5 percent). Drought stress had not a similar effect on harvest index in three genotypes. At all stress levels, water use efficiency, harvest index and dry matter had a higher direct effect on seed yield, respectively. Also, the results showed that the negative correlation between seed yield and evapotranspiration was not significant.
ConclusionsTotal dry matter was similar in the three genotypes but Bastan cultivar was better than the other lines and it is advisable to drought stress conditions due to higher water use efficiency and harvest index. As respects high crop water use efficiency is necessary for adaptation and resistance to drought stress and harvest index is an indicator of the amount of product to be used, WUE and HI can be used to identify suitable genotypes and cultivars for water shortages and drought conditions.