The Effect of Deficit Irrigation on Yield and Its Related Traits in Promising Chiti Bean (Phaseolus vulgaris L.) Genotypes under Zanjan Province Climatic Condition

IntroductionGiven that successive droughts, particularly recent ones, have impacted most regions of Iran, drought stress is recognized as one of the major challenges for crop production in the country's arid and semi-arid regions. Beans grow in a wide range of areas that are subject to seasonal droughts and wide fluctuations in soil moisture in different years. Nevertheless, drought stress causes a significant decrease in bean seed yield, and the amount of yield decrease is different depending on the time, stress intensity and studied genotype. Due to environmental conditions in areas where bean cultivation is common, water deficit may occur more than once during the crop growth cycle. In addition, when a dry period (two to three weeks) occurs, especially during flowering, yield reduction will be significant. Drought-adapted cultivars in beans require less water for irrigation and thus help conserve water resources. Despite the desire of farmers to maximize the use of irrigation to increase production in dry and semi-arid conditions, even in the absence of water restrictions, excessive irrigation is not logical; therefore, in such a situation, the efficiency of water consumption in the farm should be optimized. Deficit irrigation is an optimization strategy that purposefully allows the plant to tolerate some degree of deficit irrigation and reduced yield. Several studies show that lack of irrigation causes a significant decrease in the number of seeds, seed weight, number of fertile pods, number of seeds in pod, seed yield, biological yield and harvest index. Of the two main components of seed yield (seed number and seed weight), seed number shows higher sensitivity to water deficit. In this regard, in this research, it has been tried to evaluate the effects of drought stress on yield and yield components in 16 genotypes and cultivars of chiti beans and determine the genotypes with optimal yield under water limitation conditions. Materials and MethodsIn order to investigate the effects of deficit irrigation on some phenological and yield traits of chiti beans, 14 promising chiti bean genotypes obtained from breeding programs along with Sadri and Kosha control cultivars, in two consecutive crop years from 2022 to 2023, at Kheirabad Zanjan Research Station, in two conditions normal irrigation (irrigation cycle of 5 days) and deficit irrigation (irrigation cycle of 9 days) were investigated. The experiment was performed at both conditions and in both years, as basic of complete randomized blocks design with 3 replications. Combined variance analysis and mean comparisons were performed and simple correlation coefficients between traits and stepwise regression analysis of traits affecting grain yield in both irrigation conditions were calculated. Results and Discussion Variance analysis showed that there was a significant difference between the 5 and 9 day irrigation cycles in the number of plants per plot and the number of pods per plant at the 1% level, and in the plant height and yield at the 5% level. There was significant difference between genotypes in terms of all the studied traits (except the number of plants in plot) at the probability level of 1%. Irrigation cycle of 9 days decreased plant height, seed yield and its components including number of pods per plant, number of seeds per pod and 100 seed weight. G8, G10, G14 and G15 genotypes had the highest and G13 and G2 genotypes had the lowest seed yield. Correlation analysis showed that in irrigation cycles of 5 and 9 days, there is the highest relationship between seed yield and the number of pods per plant. On the other hand, in the 5-day irrigation cycle, the number of pods per plant, the number of seeds per pod, and the 100 seed weight, and in the 9-day irrigation cycle, only the number of pods per plant were included in the regression model and had the greatest impact on seed yield. ConclusionsThe number of pods per plant, the number of seeds per pod and the 100 seed are considered the most important components affecting seed yield and by justifying the large amount of changes in seed yield, they can be used as important traits to improve bean yield in breeding programs in different conditions. Therefore, G8 genotype with the highest number of pods per plant and high weight of 100 seeds can be introduced as a favorable genotype for cultivation in dry conditions.