Effects of drought stress on seed yield and some biochemical traits of new Faba bean lines (Vicia faba L)

Introduction Faba bean (Vicia faba L.) is a rich source of phosphorus, calcium, iron, and protein and is very effective in rotation, cropping patterns, and in maintaining the sustainability of agricultural systems and fixing atmospheric nitrogen through symbiosis. Achieving figures with high performance and a wide range of adaptation to drought stress and climatic changes is one of the most important breeding goals in Faba bean (Vicia faba L). This study was conducted to evaluate the effects of drought stress on grain yield and some biochemical traits of new Faba bean lines. Materials and methods This experiment was carried out in the crop year of 2022-2023 in the form of a split-plot experiment in the form of randomized complete blocks design with 3 replications at the Gorgan Agricultural Research Station. In this study, 9 low tannin lines of Vicia faba L along with two control cultivars Mehta (low tannin) and Shadan (high tannin) were compared and evaluated in two environments of drought stress (after flowering) and normal irrigation. The lines studied in this experiment were selected and cultivated from the superior lines of the preliminary faba bean experiments. Each experimental unit was in four lines with a distance of 60 cm, a length of 6 m and a plant distance on the row of 8 cm. In the normal irrigation environment (without stress), the time required for irrigation was based on weather conditions and the water requirement of the plant (sowing, before flowering, the beginning of flowering and seed filling) in four irrigation times so that the plant does not face drought stress, but in the drought stress environment, no irrigation was done from the beginning of flowering to the end of the growing season. Results and discussion The results of composite variance analysis (mean square) showed that the interaction between drought stress and variety on chlorophyll b, total chlorophyll, proline, soluble sugar, carotenoid, number of branches per plant and number of pods at a statistical level of 1% and on chlorophyll a and weight Seed dryness in the plant was significant at the five percent level. Comparison of the average interaction between drought stress and variety showed that Shadan variety and lines BPL4104, WRB1-3, FLIP03-07FB had the highest seed yield per hectare with 5100, 4950, 4750, 4633 kg respectively. Also, in the conditions of drought stress, FLIP03-07FB, WRB1-3 and Shadan varieties had the highest production of 500, 473 and 437 kg of seed yield per hectare, respectively. In the normal environment, Shadan variety had the highest amount of chlorophyll a, chlorophyll b, total chlorophyll and carotenoid at 1.53, 0.46, 0.2 and 0.58 mg g-1 respectively, and the line FLIP03-07FB with 9.47 μmol ml-2 had the most proline and line S2008,033 with the amount of 1.16 mg per gram had the most soluble sugar. The highest number of seeds per pod (3.28) was obtained in normal environment and the lowest number of seeds per pod (0.303) was obtained in drought stress environment. Identifying drought-resistant cultivars at the end of the season is one of the strategies for developing faba bean cultivation in the country. Drought stress during flowering and pod formation reduces the transport of photosynthetic materials, resulting in grain shrinkage, reduced grain weight, and reduced grain yield, while lack of stress during the flowering stage increases the length of the grain filling period, increases grain weight, and grain yield. Conclusion According to the results, it can be stated that drought stress in the flowering and seed filling stage caused a decrease in seed yield and an increase in carotenoid, proline and soluble sugar levels in all cultivars. Shadan variety and lines WRB1-3 and FLIP03-07FB had the highest seed yield in both environments. Therefore, the cultivation and development of two new lines are suggested after carrying out compatibility tests in different regions of the country and achieving the stability of seed yield.