Among the most common problems and stress in the conditions of Khuzestan is heat stress at the end of the season and abiotic stress, the lack of nutrients, which in different periods of rapeseed growth, depending on their severity, causes physiological and metabolic disorders and ultimately reduces the performance of rapeseed plants with different intensity depending on the type of plant genotype, they affect.
Materials and Methods
With the aim of evaluating the growth and yield response of rapeseed cultivars (Brassica napus) to boron element levels in late season heat stress conditions caused by late sowings dates, this study is a split-split plot in the form of a randomized complete block design with three replications. It was carried out in the agricultural year of 1401-1400 in the research farm of Khuzestan University of Agricultural Sciences and Natural Resources. Sowings dates (November 21, December 11, and December 31) in the main plots, four levels of boron (zero, 4, 8, and 12 kg/ha) in the subplots and rapeseed cultivars (RGS, Zafar, and Saffar) in the sub-sub-plots were investigated.
Results and Discussion
The results of the research showed that sowing date and end of season heat stress in Khuzestan conditions had a significant effect on most of the studied physiological traits, seed yield and biological. Also, the effect of boron on traits such as leaf area index, leaf area ratio, relative moisture content of leaf water, leakage of electrolytes, grain yield and biological performance was significant. The triple interaction effect of planting date, boron and variety was also significant on traits such as relative moisture content of leaf water, leakage of electrolytes, grain yield, biological performance. So that with the delay in planting and the consequent increase in temperature and heat stress at the end of the season in the period of growth and development and in other sensitive periods of the rapeseed plant, it causes a decrease in traits such as leaf area index, relative moisture content of leaf water, leaf area ratio, leaf specific area, seed yield and biological yield. And conversely, due to the heat stress of the end of the season, the leakage of electrolytes and the shade tempCan increased. In general, the highest seed yield was obtained in Safar variety on the sowing date of December 11 and the boron level was 4 kg/ha with an average of 4590 kg/ha. Also, the highest average leaf area index was observed on the first sowing date and Safar variety with an average of 5.43 and the lowest value was observed on the third sowing date and Safar variety with an average of 2.11. It was also observed that the application of boron caused a significant decrease in the leaf area index in all three studied cultivars. This issue can indicate the lower need of boron consumption of the studied cultivars in this experiment.
In general, the heat stress at the end of the season, which occurs in different periods of rapeseed growth, especially the seed filling period, depending on its intensity, causes physiological disorders in the plant and finally affects the grain yield with different intensity and depending on the genotype of the plant. The analyzed rapeseed genotypes also showed tolerance to different levels of boron element in the heat stress conditions of the end of the season and showed different reactions with different amounts of boron consumption per hectare.
Keywords: grain yield, heat stress, Khuzestan, leakage of electrolytes, leaf area index