| چکیده انگلیسی مقاله |
Introduction and Objectives: Canola (Brassica napus L.) has become the third most valuable edible oilseed crop worldwide after soybean and oil palm. Considering the importance of canola cultivation, it is important to identify genotypes with high yield potential to obtain superior crosses. Combining ability can determine the capacity of individual towards the transmission of superior performance to its offspring. Diallele analysis is used as a very powerful and efficient method to estimate genetic parameters, gene function, special and general combinability, and determine the amount of heterosis. Therefore, in this study, diallele crossing was used in eight spring and winter cultivars to estimate the combinability and heterosis of these cultivars in terms of phenological and morphological traits to identify promising parents and hybrids for future breeding programs.
Materials and methods: Four spring canola cultivars (RGS, Asa, Baharan, Dalgan) and four winter cultivars (Zarfam, Nima, SLM2246, Okapi) were crossed in 2022-2023 as a one-way diallele design. The hybrids of the first generation along with eight parents (36 genotypes in total) were evaluated in the randomized complete block design with three replications in the 2023-2024. The studied traits included the number of days to flowering, number of days to maturity, plant height, length of the main branch, number of sub-branches, number of pods in the main branch, number of pods in the sub-branch, pod length, number of grains per pod, weight of 1000- grains and seed yield.
Results: The results of diallele analysis in both general combinability (GCA) and specific combinability (SCA) showed a significant difference among the parents and hybrids for all investigated traits; therefore, additive and non-additive components play a role in the inheritance of all traits. On the other hand, in all studied traits, the estimates of GCA variances were higher than SCA variance, indicating that additive variance was more than the non-additive variance. Genotypes RGS, Asa, Baharan and Dalgan with negative and significant general combinability for the number of days to flowering will be prioritized to reach early cultivars. The results of specific combinability in six crossing for this trait were observed as negative and significant. Most crosses with negative and significant specific combinability had at least one parent with negative and significant general combinability for this trait. In terms of plant height, RGS and Dalgan genotypes showed significant negative general combinability. Six hybrids had negative and significant specific combinability for plant height, so they can be used to reduce height in breeding programs. In terms of increasing the number of pods in the main branch of the Baharan, Dalgan, Asa genotypes and the number of pods in the sub branch of the Nima, SLM046 and Okapi genotypes, there was a positive and significant general combinability. Therefore, these genotypes will be prioritized to increase these traits. In addition, positive and negative specific combinability was observed in crosses for these traits. Asa, Baharan and Zarfam genotypes with positive and significant general combinability were recognized as the best combiners to increase the number of seeds in the pod. Seven hybrid compounds with positive and significant specific combinability were recognized as superior compounds for increasing this trait. Asa and Dalgan genotypes with significant positive general combinability were considered among the desirable genotypes for increasing grain yield. Specific combinability was observed positively and significantly in 11 crosses, which indicated the non-additive effect of genes to increase this trait. The degree of heterosis compared to the superior parent for the trait number of days to flowering in most of the crosses was significant in the negative direction, which in terms of reaching early varieties of RGS×Okapi, Baharan×Okapi and Asa×Okapi crosses with significant heterosis will be given priority. Considering the desirability of shortening in rapeseed, RGS×Asa and RGS×Zarfam crosses with significant negative heterosis are preferred for height reduction. The crosses SLM046×Okapi and Asa×Zarfam had the highest amount of heterosis in the number of pods in the main branch. The crosses of Nima×Okapi, SLM046×Okapi and Baharan×Dalgan with the highest amount of heterosis will be prioritized to improve the number of pods in the branch. RGS×Okapi, Baharan×Dalgan, Asa×Okapi and RGS×Zarfam crosses had significant positive heterosis in terms of the number of seeds in the pod. In terms of grain yield, Dalgan×Okapi, Dalgan×SLM046, Zarfam×SLM046, Baharan×Zarfam, and Nima×Okapi crosses are preferred with the highest amount of heterosis.
Conclusion: The estimation of traits' combinability showed that RGS and Dalgan cultivars were the best general combiners to reducing the number of days to flowering, the number of days to maturity and the height of the plant. Therefore, these cultivars can be considered as a source of desirable alleles to achieve early maturity. In addition, Asa and Baharan cultivars were recognized as the best combiners in order to increase yield and some related traits. Nima×Okapi, Dalgan×Okapi, RGS×Dalgan and Asa×Okapi crosses were the best specific combiners hybrids for increasing yield and some related traits, while these crosses showed positive and high heterosis in seed yield. Therefore, their parents can be suggested for the production programs of new cultivars and improvement of canola genotypes for seed yield.
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