Determination of drought stress indices in corn (Case study: Behbahan)

Drought stress is the most important factor limiting the growth and grain yield of maize (Zea mays L.). Drought stress is one of the most important abiotic stresses that can seriously reduce crop yields depending on the season and the time it occurs. In arid and semi-arid regions, the plant undergoes periods of dehydration during its growth and must be able to tolerate these periods to produce proper yield (Emam and Niknejad, 2004). Cooper et al. (2006) reported that the capacity and ability to produce different maize genotypes under drought stress varied according to their morphological and physiological characteristics. Corn at different stages of development requires different amounts of water. The effect of dehydration on maize plants is marked by certain symptoms. These symptoms are seen as decreasing plant height and root length, delay in plant growth, leaf area depletion, seed production and biomass (Cakir 2004). The results of correlations indicate a significant positive relationship between potential yield (without stress) with MP, GMP, STI, TOL and HARM indices. The most positive and significant correlation between indices was related to GMP and STI (0.99) (Alipour et al, 2014). Due to the importance of maize as one of the important cereals in Iran, using irrigation method can be adapted to water shortage during drought. The purpose of this study was to investigate the effect of drought stress through different irrigation intervals and identify superior cultivar based on stress indices.

In order to investigate the response of new maize cultivars to water stress, an experiment was conducted at Behbahan Agricultural Research Station with latitude 50°:14´ east and 30°:36´ north latitude as a split plot in a randomized complete block design with four replications. It was implemented in two years (2014 - 2015). Drought stress including irrigation after 100 and 200 mm evaporation from Class A pan in main plots and three maize cultivars (S.C. 704, PH3 and PH4) were compared in sub plots.

Comparison of mean water use efficiency in irrigation and cultivar interactions showed that 100 mm evaporation from Class A pan and V2 cultivar with yield of 1.299 kg maize per 1 m3 of water was in the first rank and position. The 100 mm evaporation treatment of Class A pan and cultivar V2 was ranked second with production of 1.155 kg of maize grain per cubic meter of water. Pearson correlation coefficient results showed that the highest correlation of grain yield with water use efficiency and 1000-grain weight were calculated as 0.8761 and 0.8478, respectively, indicating the effective role of 1000-grain weight in increasing maize yield. The highest values of SSI, STI, MP, TOL, GMP, HM and YI were for V2 and the lowest for V3. The lowest YSI index belonged to V2. In other words, the accuracy of the stress and non-stress treatments in V2 indicates that the above indexes are classified as ascending and descending, respectively. Therefore, higher values of SSI, STI, MP, TOL, GMP, HM and YI in each cultivar showed that the cultivar is resistant to drought stress or deficit irrigation. Therefore, the drought tolerant cultivar identification criterion can be high values of SSI, STI, MP, TOL, GMP, HM and YI. Thus, the values of the above indices and their use in selection of drought tolerant cultivars indicate an increase in grain yield under stress and non-stress conditions and can be recommended together to identify suitable cultivars for each condition.

Comparison of mean interaction effects between irrigation and cultivar in terms of water use efficiency showed that water use reduction in stress treatment decreased water yield in this treatment compared to non-stress treatment. The effect of reducing water use was even to the extent that it failed to cover the continuous decrease in yield in return for water consumption, and the treatment of 100 mm evaporation from Class A pan despite still consuming more water than the 200 mm evaporation treatment from Class A pan. Due to the increase in performance, water consumption was the most efficient. Positive and significant correlations of yield components with important traits of 1000-grain weight on one hand and highly significant correlation of 1000-grain weight with yields on the other hand indicate that the trend of increasing yield components with grain yield increased. Drought stress tolerance index was higher than other cultivars for SSI, STI, MP, GMP, HM and YI indices.