برآورد فاکتورهای ژنتیکی و پاسخ ارقام مختلف چغندرقند (beta vulgaris l.) نسبت به دماهای پائین در مرحله رسیدگی

چغندرقند دارای پتانسیل عملکرد بالایی است، امّا تنش های مختلف از جمله سرما مهمترین عوامل کاهش دهنده عملکرد آن در سطح جهان است. برای بررسی تحمل به سرما در مرحله رسیدگی ده رقم مورد کشت چغندرقند، آزمایشی به‌صورت طرح کامل تصادفی در سه تکرار در دانشگاه یاسوج به اجرا درآمد. ژنوتیپ ها در معرض چهار سطح دمایی شامل 0، 5، 10 و 25 (شاهد) درجه سانتی‌گراد درون اتاقک رشد با دمای مورد نظر قرار گرفتند. صفات مهم کمّی و کیفی اندازه‌گیری شدند. نتایج حاصل از تجزیه واریانس نشان دادند اثر دما برای کلیه صفات اندازه گیری شده، اثر ژنوتیپ برای تمام صفات بجز قطر ریشه، نشت الکترولیت و fv/fm و برهمکنش دما و رقم برای تمام صفات اندازه گیری شده بجز نشت الکترولیت معنی دار بودند. بنابراین ارقام مورد بررسی واکنش های متفاوتی نسبت به سطوح مختلف دمایی مورد بررسی داشتند. بیشترین کاهش صفات در دمای صفر درجه نسبت به شاهد، مربوط به وزن خشک اندام هوایی به میزان 55 درصد و بیشترین افزایش مربوط به میزان پرولین برگ به میزان 58 درصد بود. وزن قند همبستگی ژنتیکی مثبت و معنی داری با صفات وزن ریشه (غده)، قندهای محلول، عیار قند و وزن خشک اندام هوایی داشت، در حالی که با صفات طول غده و شاخص کلروفیل همبستگی منفی نشان داد. گروه بندی ارقام توسط نمودار سه بعدی حاصل از امتیاز سه عامل اول ارقام پرشیا و آنتیک را متحمل تر نسبت به سرما در مقایسه با سایر ارقام تشخیص داد. نتایج این پژوهش، اطلاعات ارزشمندی جهت بهبود تحمل به سرما در اختیار به نژادگران چغندر قرار می دهد.

estimation of genetic factors and the response of different sugar beet (beta vulgaris l.) cultivars to low temperatures at the maturity stage

sugar beet has a high yield potential, but various stresses, including cold, reduce its yield worldwide. to investigate the cold tolerance of common sugar beet cultivars in the maturity stage, an experiment was carried out at yasouj university in 2020. in this research, ten sugar beet cultivars (karaji, sbsi-005, shirin, rastad, anakonda, dorotea, merac, antik, zarghan, and persia.) were exposed to four temperature levels, including (0, 5, 10, and 25 (control) ℃) at maturity stage. the experiment was performed at each temperature level based on a completely randomized design with three repetitions. the results of the analysis of variance showed that the effect of temperature for all measured traits, the effect of genotype for all characteristics except root diameter, electrolyte leakage, and fv/fm, and the interaction of temperature and genotype for all measured traits except electrolyte leakage were significant. therefore, the cultivars studied responded differently to the different temperature levels studied. the highest reduction of the characteristics at 0˚c compared to the control (25˚c) was related to the shoot dry weight by 55%, and the highest increase was related to the leaf proline content by 58%. sugar weight had a positive and significant genetic correlation with the traits of root weight, soluble sugar, sugar content, and shoot dry weight. at the same time, it showed a negative correlation with the root length and spad number traits. the three-dimensional scatter plot identified persia and antic cultivars as more tolerant to cold stress than other cultivars. the results of this study provide valuable information to sugar beet breeders to improve cold tolerance. introductionsugar beet (beta vulgaris l.) is one of the twelve main plants that provide food for the world’s people. sugar beet has a high yield potential, but various stresses, including cold, reduce its yield worldwide. cold is one of the most important abiotic stresses that limit plant growth, production, and geographical distribution. the cold at the end of the growing season reduces the yield of sugar beet and has a negative effect on its quality. therefore, it is of great theoretical and practical importance to explore the mechanism of cold tolerance and to improve it in susceptible sugar beet genotypes. most of the previous studies have been conducted regarding the effect of cold stress on physiological aspects of sugar beet traits at the seedling stage.  our previous study studied the effect of cold stress on morpho-physiological traits of ten common sugar beet cultivars. there is little information about the genetic aspects of cold tolerance of common sugar beet cultivars at the maturity stage in iran. this research investigated the genetic response of sugar beet cultivars to cold stress and the genetic relationships between their important traits in cold stress conditions at the maturity stage. materials and methodsto study the cold tolerance of common sugar beet cultivars in the maturity stage, an experiment was carried out at yasouj university in 2020. in this research, ten sugar beet cultivars (karaji, sbsi-005, shirin, rastad, anakonda, dorotea, merac, antik, zarghan, and persia.) were exposed to four temperature levels, including (0, 5, 10, and 25 (control) ℃) at maturity stage. the experiment was performed at each temperature level based on a completely randomized design with three repetitions. ten days after the cold treatment application, important morpho-physiological traits, including crown height, plant height, shoot dry weight, root diameter, root length, root weight, proline content, soluble sugar, spad value, electrolyte leakage, fv/fm ratio, sugar content, and sugar weight were measured. combined variance analysis was performed, and environmental, genotypic, and phenotypic variances were calculated. genotypic and phenotypic coefficients of variation and broad-sense heritability were calculated. the pearson correlation coefficient between the measured traits was calculated, and the relationships among variables were interpreted. factor analysis was done, and the most important first components were interpreted. the three-dimensional scatter plot of the distribution of genotypes was drawn based on the first three factor scores. genotypes were classified according to their response to cold stress. results and discussionthe results of the combined analysis of variance showed that the effect of temperature for all measured traits, the effect of genotype for all characteristics except root diameter, electrolyte leakage, and fv/fm, and the interaction of temperature and genotype for all measured traits except electrolyte leakage were significant. the highest reduction of the characteristics at 0˚c compared to the control (25˚c) was related to the shoot dry weight by 55%, and the highest increase was related to the leaf proline content by 58%. broad-sense heritability of root diameter, electrolyte leakage, and fv/fm was over 50%, indicating less effect of environmental factors. proline content and total soluble sugar had a maximum genetic coefficient of variation. in contrast, sugar weight had a positive and significant genetic correlation with the traits of root weight, soluble sugar, sugar content, and shoot dry weight. at the same time, it showed a negative correlation with the root length and spad number traits. so, these traits can be used in indirect selection to improve sugar weight. factors analysis in cold conditions identified the first two factors related to cold tolerance and the third factor related to cold sensitivity. the three-dimensional scatter plot identified persia and antic cultivars as more tolerant to cold stress than other cultivars. the results of this study provide valuable information to sugar beet breeders to improve cold tolerance.  conclusionbased on the results of this research, high genetic diversity was observed for traits related to cold tolerance in sugar beet. in addition, genetic relationships among important sugar beet traits in cold conditions show that some characteristics can be used in indirect selection to improve cold tolerance in sugar beet. some traits had more than 50% heritability, which can be considered in sugar beet breeding programs. there was a relationship between cold tolerance in the vegetative stage and the maturity stage. therefore, it is possible to improve cold tolerance in the early stages of growth.