Effect of Irrigation Cut-Off Stress on growth indices and conservable grain yield of Sweet and Super Sweet Corn Hybrides (Zea mays L. var. Saccharata)

Sweet corn (Zea mays L. var. Saccharata) is one of the important and strategic crops, not only due to the short growing season for summer planting (Ti-da et al., 2006; MokhtarPour et al. 2008), but also, for the accumulation of higher quantities of sugars and the soluble polysaccharides in the grain of the endosperm, which can be consumed as a freshly, canned or frozen food. However, the occurrence of drought stress during vegetative and reproductive growth stages is one of the most important challenges to the summer planting of crops such as sweet corn (Ahmadi et al., 2013). Therefore, due to the limited water resources in agriculture, adopting any strategy to conserve water is very important. One of these strategies is irrigation cut-off. Therefore, the aim of the present study was i) to evaluate irrigation cut-off effects on growth indices and conservable grain yield; ii) to identify sweet corn varieties that could be tolerant to irrigation cut-off with slight loss in grain yield under Markazi Province climatic conditions.

In order to study the effects of irrigation cut-off stress on growth indices (leaf area index: LAI; relative growth rate: RGR; crop growth rate: CGR; net assimilation rate: NAR) and conservable grain yield of three sweet corn varieties (Merit, Chase, KSC.403) and two super sweet corn varieties (Obsession, Basin), a split-plot experiment was conducted in a randomized complete block design with three replications at Millajerd research farm of Payame Noor university of Markazi province in 2016. There were three levels of irrigation regimes assigned to the main-plots; (S0: no irrigation cut-off, S1: irrigation cut-off at the 8- leaf stage and S2: irrigation cut-off at the grain filling stage) and six corn varieties assigned to the sub-plots, respectively. All data were subjected to analysis of variance (ANOVA) using the GLM procedure of SAS statistical program. Also, significant differences among the means were measured using the least significant difference (LSD) test by pairwise comparisons (P < 0.05).

The results showed that the differences among irrigation patterns and varieties were significant in terms of the measured traits (P<0.01). In addition, the interaction effect of irrigation × varieties was significant for all of the measured traits. The results of present study showed that irrigation cut-off stress had a negative effect on growth indices and conserable grain yield; however, irrigation cut-off at the 8-leaf stage had more negative effects on the varieties and traits as compared to the grain filling stage. Based on the results, the greatest variation observed among irrigation patterns was related to LAI, RGR and conservable grain yield traits, which were affected in the descending order of the irrigation patterns (S0>S2>S1) (P<0.05). Also, the conservable grain yield as the most important economic trait, under the irrigation cut-off stress at the 8- leaf stage and grain filling stage, showed a decrease of 20.87 % (7136.18 kg.ha-1) and 7.96 % (8300.25 kg.ha-1), respectively, as compared to full irrigation (S0) (9018.42 kg.ha-1) (P<0.01). On the other hand, varieties of "Obsession" and "Basin" exhibited higher growth indicies and the least yield loss as compared with the other varieties under irrigation cut-off treatments (S2, S1) and S0 (P<0.05).

Our findings indicated that the growth indices including LAI and RGR might be suitable for the identification and selection of sweet varieties that are tolerant to irrigation cut-off. In addition, due to the limited water resources in agriculture, using irrigation cut-off pattern at grain filling stage with non-significant loss of grain yield in sweet corn varieties, especially "Obsession" and "Basin" varieties can be recommended to the farmers in the Markazi province.