Evaluation of the effect of interruption of irrigation on protein and seed oil content of rapeseed genotypes

The response of plants to drought stress conditions is related to the severity of stress and its growth stage. The amount of nitrogen and protein in oilseeds is related to the optimal storage of soil moisture. Under drought stress conditions, by reducing the grain size, oil content and protein content, it fills a large volume of grain space compared to non-stress conditions. One of the serious problems in rapeseed production is the problem of water shortage in the reproductive period. In order to solve this problem, relying on genetic potential and introducing genotypes and cultivars tolerant to drought stress is one of the practical ways.

In order to evaluation of the effect of cut-off stress on protein and seed oil content of spring rapeseed genotypes a split plot experiment was conducted based on the randomized complete block design with three replications at the research farm of department of plant production and genetics, Agricultural Sciences and Natural Resources University of Khuzestan, Iran during 2020-2021. Main plots included three irrigation treatment: control (without interruption of irrigation), interruption of irrigation in the beginning of flowering stage (phenology code 60) to the formation of 50% pods (phenology code 75) and interruption of irrigation in the stage of formation of pods until harvest (Phenology code 99) in the main plots and the genotypes (Long pod, Aram, RGS 003, Jankom, Solar, Hayola 4815, Mahtab, Julius, Agamax and Sala) were arranged in sub-plots with respect to irrigation treatments. The amount of seed oil was determined by purim method. Oil yield was obtained by multiplying the percentage of oil in grain yield by kilograms per hectare. Grain nitrogen content was calculated by Kjeldal apparatus. Protein yield was obtained by multiplying the percentage of protein in grain yield by kilograms per hectare.

The results of this study showed that the interaction effect of cutoff stress and genotype on all traits except grain protein yield was significant. The highest oil percentage and seed oil yield were observed under normal conditions by Hayola 4815, Langpad and Solar genotypes. The highest percentage of seed oil in both applied stresses was assigned to Hayola 4815, Langopad and Mahtab genotypes. Regarding grain protein content and nitrogen content, the highest amount of mentioned traits was obtained under drought stress conditions and lazy genotypes, Jankom, RGS003 and Hayola 4815. In general, under the conditions of cessation of irrigation stress, the amount of grain protein increased, however, the oil content was decreasing and a significant negative correlation was observed under normal conditions and stress between the two traits. Due to the higher values of MP, GMP, HM, STI and YI indices in terms of seed oil yield, compared to other genotypes under drought stress conditions were suggested as the superior treatment.

Under drought stress, grain nitrogen content and increase while oil grain decreases, in fact, the amount of nitrogen, oil and seed oil under irrigation stress conditions have a negative and significant correlation.