Analysis of relationships between some traits and grain yield in rapeseed for its indirect improvement under normal irrigation conditions and drought stress at end of the season

IntroductionToday, lack of water is one of the most important factors limiting crop growth in arid and semi-arid regions, and the reduction in growth caused by drought stress is far more than other environmental stresses. In order to investigate the relationships between yield and agronomic and phenological traits and to determine the relationships between these traits in spring rapeseed genotypes, seven rapeseed lines were crossed with five testers under two moisture conditions in the 2019-2020.Materials and methodsThe first generations hybrids along with 12 parents were evaluated under normal irrigation conditions and drought stress at the end of the season. Under normal irrigation conditions, irrigation was carried out in the stages of cultivation, rosette, stem growth, flowering, stem formation and grain development. Manual weeding was done to control weeds. In order to apply drought stress at the end of season, irrigation is stopped after flowering. The traits evaluated in this research included days to flowering, days to end of flowering, length of flowering period, days to physiological maturity, plant height, number of pods per plant, length of pods, number of grain per pods, height of the first pods from the ground, 1000 grain weight, grain yield per hectare, oil percentage, number of pods in the sub-branches, number of pods in the main stem, number of sub-branches, diameter of pods, length of the main stem, diameter of the stem at a height of 20 cm.Results and discussionThe correlation results of traits in normal irrigation conditions showed that grain yield had a positive and significant correlation with the traits of number of pods per plant, number of pods in sub-branches, stem diameter at a height of 20 cm, number of seeds in pod and number of sub-branches. Under drought stress at the end of the season, number of pods per plant, number of seeds per pod and diameter of pod had a positive and significant correlation with grain yield and day to flowering had a negative and significant correlation with grain yield. Based on the results of the stepwise regression analysis in both conditions, the number of pods per plant under normal irrigation conditions and drought stress justified most of the changes in the regression model. Based on the results of path analysis in both experiment conditions, number of pods per plant, thousand grain weight, number of grains per pod and the height of the first pod from the ground have direct positive effects and days to physiological maturity had direct negative effect on grain yield. Also, the length of the main stem under normal irrigation conditions and the number of pods in the sub-branches under drought stress conditions at the end of the season had direct negative effects on grain yield. However, all these negative direct effects were neutralized by positive indirect effects through other traits and caused the correlation coefficients of these traits with grain yield to become insignificant. In principle component analysis, in normal irrigation conditions, the total of 6 independent factors justifed about 75.9% of the changes, the first component including the number of pods in sub-branches, the number of pods per plant and the diameter of the stem at a height of 20 cm. In the conditions of drought stress at the end of the season, a total of 7 independent factors justified about 75.2% of the changes, the first factor consisting of the number of pods in the sub-stem, the number of pods per plant, the number of sub-branches, the diameter of the stem in the height of 20 cm.ConclusionIn general, in both conditions of normal irrigation and drought stress at the end of the season conditions, the number of pods per plant and the number of grains per pod had a high share of total changes and were the most effective traits on grain yield. Therefore, since these traits are more heritable than grain yield, selection to increase them can be recommended for indirect improvement of grain yield in breeding programs.