ارزیابی مورفولوژیک و گزینش تک درختان متحمل به تنش یخ زدگی در باغات زیتون استان گلستان

دمای پایین از تنش‌های عمده غیر زیستی است که سبب آسیب فراوان به درختان میوه می شود. آسیب سرما به درختان همیشه سبز مانند زیتون، بیشتر از بقیه گیاهان است. به علت همیشه سبز بودن زیتون، تنش سرما اغلب در اواخر پاییز، زمستان و اوایل فصل بهار علاوه بر خسارت به محصول زیتون، در رقم های روغنی دیررس، باعث خشکیدگی شاخساره سال جاری و شاخه های چند ساله می شود. این مطالعه در سال 1395 و 1396 با هدف ارزیابی خسارت یخ زدگی از دیدگاه باغبانی و شناسایی تک درختان متحمل به تنش یخ زدگی زودرس پاییزه پس از وقوع یخبندان آذر ماه 1395در باغات زیتون شرق استان گلستان انجام شد. علائم تنش یخ زدگی در درختان زیتون با توجه به نوع رقم و ژنوتیپ، شامل خشکیدگی و ریزش برگ، ترکیدگی شاخه های یک تا چند ساله، تیرگی رنگ پوست و چوب، خروج محتویات میوه و تغییر رنگ میوه بلافاصله بعد از تنش یخ زدگی تا هفت ماه بعد از تنش مطالعه شد. در ابتدا 218 تک درخت زیتون که نسبت به سرما از خود تحمل نشان داده بودند شناسایی و مجددا یک ماه، چهار ماه و هفت ماه بعد از تنش مورد ارزیابی قرار گرفتند. در نهایت، تعداد 58 اصله درخت زیتون متحمل به سرما در باغات مختلف شناسایی و از نظر صفات مکانی، عملکردی و مورفولوژیک بررسی شدند. برخی از این درختان در مناطق مختلف، الگوهای رفتاری مشابهی نسبت به تنش یخ زدگی نشان دادند و با تحقیقات تکمیلی می توان امیدوار بود از بین درختان شناسایی شده، ارقام متحمل به سرما با عملکرد قابل قبول معرفی گردد.

Morphological Evaluation and Selection of Tolerant Trees to Freezing Stress at The Olive Orchards in Golestan Province

Introduction ;Low temperature is one of the major abiotic stresses which can cause a significant reduction in olive growth and productivity mainly at late autumn, winter and early spring. Although olive is moderately freezing tolerant, temperatures below a certain threshold 7oC can damage the plant, while at 12oC damage may be serious enough to threaten the life of the tree. Different cultivars of olives have diverse reactions to cold stress and so, the selection of cold resistant cultivars is the most effective method to avoid frost damages. First step to achieve this goal, is indentifying tolerant cultivar and genotypes in olive area growing. Due to extensive and high freezing damage in November 2016, the objective of the present study was to evaluate morphological characteristics and selection of single tolerant cold trees.;Materials and Methods ;The present study was carried out in some cold tolerant olives after freezing event in December 2016 in Eastern region of Golestan province of Iran. After freezing stress Healthy olive trees were identified in tow major olive cultivation regions and then were evaluated in four stages. Thus, this study included: 1 Meteorological data analysis, 2 Evaluation of freezing stress symptoms in olive orchards and identification of single tolerant trees, 3stugy of single tolerant cold trees in 4 stages. For each genotype, studies on morphological traits (Tree age, location altitude, dip direction and its percentage, previous yield, tree height, canopy height, average of canopy diameter, canopy volume, canopy surface area, trunk perimeter, trunk diameter, trunk cross section area, length of internodes, growth habit, canopy density, canopy defoliation, barksplit ranging, flowering and fruit set) based on CFC / IOOC / 03 and Lodolini et al. (2016) results.;Results and Discussion;History of cold climate in the last two decades showed freezing event several times cause damage to olive orchards. The last freezing stress occurred with the entrance of the cold air to the Golestan province and a sudden drop in temperature to less than 0 degrees Celsius and stability of these conditions for 5days in the late of November, 2016. The temperature drops below 0 ° C began on November 23 and lasts for 4days. However, the main damage to the olive orchards is on November 25, when temperature is 7 ° C. The minimum temperature recorded in the studied regions in November 25, Maravehtapeh, Gonbad, Kalaleh and Minoudasht are 14.2, 12.7, 12.3 and 8.5 ° C, respectively. Symptoms of freezing damage on olive tree can range from shoot tip burns and defoliation up to bark split on branches or trunk. After 4 stages visiting olive orchards, Finally, from 218 primary individual trees, 58 trees were introduced for further evaluation. Location altitude (meters above sea level) of the idividual trees are 81411 in the CTO17 and CTO5 genotypes, respectively. Generally, 93% of all trees identified in sloping land orchards, and the Percentage variation for this trait is 48. 99. Fruit production of selected olives before freezing event in 2016 showed except of 13 trees, 44 of olives was of 260 kg/tree. Tree height was 26.82 in CTO35 and CTO17 genotypes, respectively. However, average of canopy diameter in all genotypes was 2.68. Also, trunk diameter (TD) and trunk cross section area (TCSA) was maximum in CTO29 and minimum in CTO9. But the average of this trait was 17.13 cm. Variation between genotype in internode length changed between 1.05 in CTO20 and 16.2 in the CTO49. Reduction of internode spaces and shoot growth, even though the total node number is normal resistance of the olive tree to cold is reduced. Leaf defoliation is one of the most important symptoms of freezing event. The study of selected trees showed that 48 trees (83%) did not showed symptoms of leaf loss, and only 10 trees showed less than 50% leaf loss. Except for the CTO54 genotype, which showed symptoms of bark spliting on oneyear shoots, no evidence of bark spliting observed in other selected olives.; Conclusions ;Although olive is the most coldhardy of the subtropical fruit trees, some varieties can withstand low temperatures better than the other. Although temperatures at which olive trees can be damaged vary, depending on climatic conditions, temperatures at or below 7°C are often critical. The most important symptoms were leaf defoliation, bark split, and limb dieback. Finally, because of different influence of environmental factor in different regions, evaluation of location, yield and morphological traits showed some of cold tolerant olive in different region had a similar behavior, thus by supplementary molecular studies, it can be hoped that among recognized trees, cold resistant cultivars with acceptable yields were introduced.