آثار تنش خشکی درازمدت و تنوع ویژگی‌های مرتبط با برگشت‌پذیری، دیرزیستی و خواب تابستانه در گونه‌های داکتی‌لیس (.dactylis glomerata l) و بروموس (.bromus inermis leyss)

این پژوهش به‌منظور ارزیابی تحمل خشکی ژنوتیپ‌های نوترکیب دو گونه داکتی‌لیس (.dactylis glomerata l) و بروموس (.bromus inermis leyss)، و بررسی اثر تنش خشکی درازمدت بر دیرزیستی، خواب تابستانه و برگشت‌پذیری اجرا شد. بدین منظور، تعداد 36 ژنوتیپ داکتی‌لیس و 36 ژنوتیپ بروموس به‌صورت تصادفی از بین نتایج حاصل از پلی‌کراس انتخاب شده و کلون شدند و در شرایط بدون تنش و تنش خشکی طی سال‌های 1394-1392 در مزرعه پژوهشی دانشگاه صنعتی اصفهان مورد ارزیابی قرار گرفتند. در سال پنجم (1395)، پس از برداشت علوفه بهاره، اجرای آبیاری به‌مدت 2 ماه در هر دو رژیم رطوبتی متوقف شد و سپس گیاهان آبیاری شده و مورد ارزیابی قرار گرفتند. تنوع ژنتیکی زیادی بین ژنوتیپ‌های هر دو گونه از نظر اکثر صفات مشاهده شد. در گونه داکتی‌لیس، ضریب تنوع ژنتیکی از 4/31 تا %65/45 در شرایط بدون تنش، و از 3/93 تا %79/93 در شرایط تنش متغیر بود. در گونه بروموس، دامنه ضریب تنوع ژنتیکی در شرایط بدون تنش %67/18-3/56 و در شرایط تنش %54/63-3/42 مشاهده شد که نشان‌دهنده پتانسیل زیاد برای بهبود این صفات از طریق انتخاب هدفمند در برنامه‌های اصلاحی است. در هر دو گونه بیش‌ترین درصد افزایش ضریب تنوع ژنتیکی تحت شرایط تنش برای صفات مرتبط با برگشت‌پذیری (امتیاز و نسبت برگشت‌پذیری در گونه داکتی‌لیس، و عملکرد، امتیاز، نسبت و درصد برگشت‌پذیری در گونه بروموس) مشاهده شد. نتایج نشان داد که گونه بروموس از نظر برگشت‌پذیری نسبت به گونه داکتی‌لیس وضعیت بهتری دارد. در هر دو گونه کاهش صفات مرتبط با برگشت‌پذیری، به‌جز صفت نسبت برگشت‌پذیری در گونه بروموس، تحت شرایط تنش خشکی مشاهده شد. میزان کاهش این صفات در گونه داکتی‌لیس نسبت به بروموس بیش‌تر بود. در این پژوهش، دیرزیستی ژنوتیپ‌های داکتی‌لیس در رژیم رطوبتی تنش خشکی افزایش یافت در‌حالی‌که در گونه بروموس کاهش یافت. تولید کم‌تر علوفه طی تابستان توسط ژنوتیپ‌های این ژرم‌پلاسم نشان داد که این ژنوتیپ‌ها دارای خواب ناقص بودند. 

effects of long-term drought stress and variation in traits related to post-drought recovery, persistence, and summer dormancy in two species of orchardgrass (dactylis glomerata l.) and smooth bromegrass (bromus inermis leyss.)

abstractthis study was conducted to evaluate drought tolerance of recombined genotypes of orchardgrass (dactylis glomerata l.) and smooth bromegrass (bromus inermis leyss.), and investigate the effect of long-term drought stress on persistence, summer dormancy, and post-drought recovery. for this purpose, 36 genotypes of each species randomly selected from polycross populations, were clonally propagated, and evaluated under normal and drought-stressed conditions during 2013-2015 at the research farm of the isfahan university of technology, isfahan, iran. in the fourth year (2016), irrigation was withheld in both moisture regimes for two months, and then plants were re-watered and investigated. for most of the measured traits, high genetic variation was observed among the genotypes of both species. in orchardgrass, the genetic coefficient of variation varied from 4.31 to 65.45% under normal conditions, and from 3.93 to 79.93% under drought stress conditions. in smooth bromegrass, the range of genetic coefficient of variation was variable from 3.56 to 67.18% under normal conditions and from 3.42 to 54.63% under drought stress conditions. this indicated a high potential for improving these traits through targeted selection in breeding programs of the two species. in both species, the higher increase in genetic coefficient of variation under drought stress was observed for recovery-related traits (i.e., degree of recovery and recovery ratio in orchardgrass; and recovery yield, degree of recovery, recovery ratio, and percentage of recovery in smooth bromegrass). results showed that smooth bromegrass had a better performance regarding recovery-related traits. furthermore, post-drought recovery-related traits in both species were reduced under drought stress, except for the recovery ratio in smooth bromegrass. however, reductions were higher in orchardgrass than in smooth bromegrass. in the current study, the persistence of orchardgrass genotypes increased under drought stress, and decreased in the smooth bromegrass. less fodder production during summer by the genotypes of this germplasm showed that these genotypes had incomplete dormancy.background and objective: orchardgrass (dactylis glomerata l.) is one of the most important perennial forage grasses, which plays an essential role in the livestock industry and sustainable development of environments worldwide (2). smooth bromegrass (bromus inermis leyss.) is a drought-tolerant, cool-season grass species grown mainly for hay production (1). drought stress is one of the most important factors limiting the survival and growth of plants in many regions of the world. therefore, grasses must survive summer, recover in autumn, and actively grow during the cooler rainy seasons. despite the wide distribution of forage grasses in arid and semi-arid regions of iran, studies about post-drought recovery, persistence, and summer dormancy in these two species are rare. therefore, this study was conducted to: 1) evaluate the genetic variation of post-drought recovery, persistence, and summer dormancy under two moisture conditions, 2) determine the relationships between these traits with phenological traits, productivity, and drought tolerance, and 3) assess the response of genotypes to drought stress in terms of the evaluated traits.methods: in this study, 36 genotypes of each species were randomly sampled from polycross progenies. these genotypes were clonally propagated and space-planted in the field according to a randomized complete block design with 12 replications in march 2012. six replications were allocated to each of the two moisture environments. phenological and morphological traits were evaluated over three years. after three years of field evaluation, drought recovery of all genotypes was assessed in 2016. for this purpose, after the first harvest of the fourth year, acute drought stress was imposed on both previous moisture environments (normal and drought stress) by stopping irrigation for 60 days until grass foliage was entirely desiccated. all plants were irrigated to the point of field capacity every week to allow drought stress recovery. after six weeks of re-watering, the traits related to recovery were measured.results: high genotypic variation was observed among genotypes for all measured traits, indicating a high potential for improving these traits. drought stress negatively affected all traits and reduced their diversity. moreover, in both species, after withholding irrigation and re-watering, post-drought recovery of genotypes was reduced under drought stress. however, these reductions were higher in orchardgrass than in smooth bromegrass. in this study, the persistence of orchardgrass genotypes increased under drought stress, and decreased in smooth bromegrass. the reduction of persistence under drought stress is likely related to decreased crown diameter, less root growth, and a decrease in growth points. results also revealed that the genotypes of this germplasm with the characteristic of inhibiting fodder production during summer had incomplete dormancy. these plants were more flexible to drought stress. they had better survival and persistence than the plants with low summer dormancy, indicating that summer dormancy is an important trait for drought tolerance and can be used to develop drought-tolerant cultivars.conclusions: there was high genetic diversity between the studied genotypes of both species, which can be used in the breeding programs. in both species, post-drought recovery of genotypes was reduced under drought stress. these reductions were higher in orchardgrass than in smooth bromegrass. in the current study, the persistence of orchardgrass genotypes increased under drought stress conditions, while it decreased in smooth bromegrass. moreover, the genotypes of this germplasm with the characteristic of inhibiting fodder production during summer had incomplete dormancy. there was a significant and positive association between summer dormancy and autumn yield on the one hand and between autumn yield and productivity on the other. therefore, autumn yield is a compensatory mechanism in the dormant genotypes during the summer, leading to more fodder production in these genotypes during the autumn. references:1. casler, m.d., vogel, k.p., balasko, j.a., berdhal, j.d., miller, d.a., hansen, j.l., frits, j.o., 2000. genetic progress from 50 years of smooth bromegrass breeding. crop science 40: 13–22.2. jiang, l.f., qi, x., zhang, x.q., huang, l.k., ma, x., xie, w.g. 2014. analysis of diversity and relationships among orchardgrass (dactylis glomerata l.) accessions using start codon-targeted markers. genetics molecular research 13(2): 4406–4418.