Study of drought stress susceptibility indices of forage maize cultivars under water limited conditions and salicylic acid application

Water deficiency affects photosynthesis, respiration and transpiration by affecting cellular swelling and opening and closing openings. Also, by affecting enzyme processes directly controlled by water potential, it negatively affects plant growth (Brar et al., 1990). Salicylic acid is a phenolic compound and has an antioxidant effect in regulating the physiological processes of plants. Salicylic acid is known as an important messenger molecule in plant responses to various biotic and non-biological stresses (El-Tayeb, 2005). Salislic acid increases wheat and corn resistance in salt conditions (Gunes et al., 2007). Salicylic acid also increases the resistance of plants to biological and non-biological stresses such as drought stress (Sing and Usha, 2003). The aim of this experiment was to evaluate the susceptibility indices of early maize, medium clay and late corn varieties. For this purpose, stress tolerance indices were used to estimate yield in stress and non stress conditions, so that the most suitable indices or indicators of stress tolerance along with superior genotype were determined. In order to evaluate the study of stress susceptibility Indies of maize cultivars under water stress and salicylic acid application, this study was carried out in field of Arak Payam Noor university in 2009. Twice split-plot arrangement of treatment in a randomized complete block design with three replications was used. Water stress (I0= Control irrigation, I1= Irrigation about 80% plant requirement water, I2= Irrigation about 60% of plant requirement water, were assigned in the main plots, maize varieties (V1= S.C 370, V2= Apex, V3= S.C 704) in sub plots and foliar treatment of salicylic acid in two levels (Sa0= Control, Sa1= 300 ppm) in sub-sub plots. Each sub plot consisted of 4 rows, 5 m long with 50 cm between rows space and 20 cm between plants on the rows. In this study characteristics such as: stem height, panicule length, number of ear m-2, ear height, forage biomass, stress susceptibility index, tolerance, mean productivity, geometric mean productivity, stress tolerance index, yield index and yield stability index were assessed. After analyzing the data, the meanings were compared with Duncan's multiple range tested at a probability level of 5%. Also, all correlation coefficients between studied traits were calculated and their significance was determined by Mstat-c software. In the analysis of variance table, the effects of treatment of water stress levels and different maize varieties on the biomass traits were significant at 1% probability level. So that among the levels of water stress, the highest amount of forage biomass with mean 40.3 ton ha-1 and the lowest is the average 28.06 ton ha-1 related to intense water stress treatment. In this study, the use of the TOL indicator showed that the Apex hybrid had the lowest value (7.45) and the hybrid S.C 370 with the amount of (9.09) respectively, had the highest and lowest levels of water stress tolerance among cultivars. SC 704 cultivar with average (1.18) the highest tolerance to stress was achieved.
Results indicated that the treatment effect of water stress on traits such as panicule length, number of ear m-2, forage biomass was significant. The treatment effect of cultivars of maize on traits such as stem height, panicule length, ear height and forage biomass was significant, too. The S.C 704 hybrid was markedly superior performance than other cultivars in stress susceptibility index, mean productivity, stress tolerance index, geometric mean productivity, yield index and yield stability index. According to the results of this study, with increasing water deficit stress, forage yield decreased by about 30%. However, with normal irrigation, the highest silage yield was obtained. Among cultivars, S.C 704 had a remarkable advantage. Also, Salicylic acid increased forage yield, although this increase was not significant.