Investigation of frost stress on yield, yield components and a number of biochemical traits in rapeseed genotypes

Rapeseed is one of the most important oilseeds in the world. Rapeseed with the scientific name of Brassica napus L. is ranked third in the world in terms of grain production after soybean and in terms of oil production after soybean and oil palm. Plants are always exposed to a wide range of environmental stresses, both biological and non-biological, that strongly affect their growth and production. Cold stress and frost are one of the environmental factors that affect crop production and other important agronomic traits in many plant species. Frost in the early stages of germination causes the destruction of the whole plant. The amount of frost damage depends on many important factors such as the duration and severity of frost stress, different stages of plant growth period and the amount of air humidity. Rapeseed is sensitive to frost stress and shows a yield reduction of up to 70%.Identifying cultivars that tolerate low temperatures can help researchers improve new cultivars and increase the flexibility of choosing the right planting date for farmers. Various studies have been performed to evaluate canola genotypes against cold stress in terms of morphological or physiological traits, but few studies have been conducted to study the combined traits. This study was designed to identify frost stress resistant genotypes, evaluate the effects of frost stress on yield and yield components as well as physiological traits to identify and modify the traits affected by the stress.

In this experiment, 24 autumn Rapeseed genotypes were obtained from the oilseeds section of Karaj Seed and Plant Breeding Research Institute. Selected genotypes included a number of promising lines and free pollen and rapeseed hybrid cultivars, including: SLM046, Opera, L963, Okapi, L62, Nima, KH4, Talayeh, L957, Ahmadi, KR18, L1009, Zarfam, Nafis, HW101, Licord, KS7, L14, SW101, L1008, L83, L120, Natali and Hydromel. Experiment with two different planting dates as normal sowing on 10/6/1397 and delayed sowing on 6/25/1397 in the form of split plot design based on randomized complete blocks with three replications in 1397-98 crop year It was implemented in the agricultural lands of Tikmeh Dash city of East Azerbaijan province. Morphological traits including number of pods per plant, number of seeds per pod, 1000-seed weight, yield per hectare and physiological traits including leaf chlorophill, proline, malondialdehyde, soluble sugars, electrolyte leakage percentage and superoxide dismutase were measured.

The effects of frost stress were significant for three traits: number of pods per plant, 1000-seed weight and yield at 1% probability level, and this indicates that delay in planting all cultivars tested caused a decrease in yield and its components. The mean squares of genotypes were significant for two traits: number of seeds per pod and yield at 1% probability level. Mean stress squares were significant in terms of chlorophill b, proline, soluble sugars, electrolyte leakage, malondialdehyde and superoxide dismutase at the level of 1% probability. There was also a significant difference between the genotypes in terms of the above traits as well as chlorophill a and total chlorophill at the level of one percent probability. The results of comparing the mean of genotypes together for stress-free and frost stress conditions showed that KS7 line with 1699.9 kg ha-1 had the highest average yield and the lowest was related to L62 line with 107 kg ha-1. According to this study, the decrease in yield is due to the decrease in the number of pods per plant as components of grain yield. Both under stress and non-stress conditions, the total yield showed a positive and significant correlation with the number of pods per plant and the number of seeds per pod. In non-stress conditions, no correlation was observed between yield and physiological traits, while in frost stress conditions, there was a positive and significant correlation between yield with proline, soluble sugars, malondialdehyde and superoxide dismutase, so this can be Introduced traits as positive traits for selecting frost-resistant cultivars. Based on the results of factor analysis, 4 factors were identified for each of the conditions without stress and frost stress, which in the non-stress state was 77.52% of the total variance and in the frost stress state was 81.06% of the total variance.

According to the results of the correlation between the studied traits, it was found that in non-stress conditions, the number of pods per plant and the number of seeds per pod can be used to improve grain yield. In terms of frost stress, in addition to the number of pods per plant and the number of seeds per pod, the amount of proline, soluble sugars, malondialdehyde and superoxide dismutase had the greatest contribution in justifying the diversity of studied genotypes. Due to the low heritability of the yield, it is usually difficult to improve. As a result, other aspects of frost stress resistance, such as physiological parameters, should be considered. In general, physiological traits provide more complete information and are a good alternative to functional traits.