سطوح نسبی مقاومت به بلایت باکتریایی در تعدادی از ارقام و ژنوتیپ‌های انتخابی گردو

کاشت ارقام مقاوم یکی از مهم ترین راهکارهای کنترل بیماری بلایت باکتریایی گردو با عامل xanthomonas arboricola pv. juglandis است. در این تحقیق، سطوح نسبی مقاومت به بلایت باکتریایی در برگ و میوه نارس برخی ارقام تجاری و ژنوتیپ های انتخابی گردو در دو سال تکرار بررسی شد. ارقام و ژنوتیپ های مورد بررسی شامل kz3، 882، 881، g3، shk2، c25، h21، h17، h11 و رقمshinova  بوده و ارقام تجاری serr، hartley و chandler به عنوان شاهد به کار برده شدند. برای ارزیابی مقاومت میوه نارس، علاوه بر مواد فوق، ارقام و ژنوتیپ های vina، round de montignac (rdm)، lara، g4، g5، b10، k15، h18 و h212 نیز گنجانده شدند. از میان مواد گیاهی ارزیابی شده، چهار ژنوتیپ داخلی kz3، 882، 881 و g3 در سال 1398معرفی شدند. مخلوط جدایه های باکتری عامل با منشا قزوین، کرج، زنجان و ارومیه در تهیه مایه تلقیح به کار برده شد. ارزیابی مقاومت برگ در شرایط گلخانه و با اسپری نهال های پیوندی انجام شد و بررسی مقاومت میوه نارس در شرایط آزمایشگاهی و با مایه زنی میوه های 45 روزه صورت گرفت. بر اساس نتایج، شدت بلایت برگ و میوه نارس در ارقام و ژنوتیپ های مختلف در هر دو سال ارزیابی متفاوت بود. نتایج تجزیه مرکب داده‌ها نشان داد که ژنوتیپ های g3 (الوند) و 882 (پرشین) حساس ترین و رقم hartley مقاوم ترین برگ و ژنوتیپ های h11 و shk2 به ترتیب حساس ترین و مقاوم ترین میوه نارس را داشتند. میانگین شدت بلایت برگ و میوه نارس در سال های اول و دوم تفاوت معنی داری نداشت. بر اساس مقایسه ارقام صورت گرفته در این تحقیق، ارقام داخلی تازه معرفی شده پرشین، کاسپین، الوند و چالدران از نظر مقاومت نسبی برگ به ترتیب حساس، نسبتاً مقاوم، حساس و نسبتاً حساس و از نظر مقاومت نسبی میوه نارس به ترتیب مقاوم، مقاوم، نسبتاً مقاوم و حساس بودند. ارتباط آماری بین شدت بلایت برگ و میوه نارس دیده نشد.

Relative Resistance Level to Bacterial Blight in a Number of Walnut Cultivars and Selected Genotypes

Introduction: The major disease of Persian walnut is walnut blight caused by the bacterium Xanthomonas arboricola pv. juglandis. This disease limits walnut production in many regions of the world in particular those with warm and humid springs. All succulent tissues including recent shoots, fruits and catkins may be attacked but their sensitivity decreases over time. Symptoms on leaves begin as small, watersoaked spot that can expand to form angular necrotic lesions surrounded by a yellow hallo. Infection on the hull of the unripe fruits is initiates as a dark spot, which rapidly creates dark sunken lesions. If fruit infection occurs before shell hardening, the kernels are usually destroyed, infection after shell hardening results in dark kernels and poorquality nuts, while the kernel is until consumable. The main current strategy for walnut blight control is to protect succulent tissues by copperbased sprays from budburst. However, multiple copper sprays do not always control the disease and there is the risk of development of copper resistant bacterial strains. Cultivation of resistant cultivars is the most practical, environmental friendly and economical approach for controlling of this disease. So far, there have not been any cultivar completely resistant or immune to this disease. However, variation in susceptibility level has been shown to occur, worldwide. The objective of this study was to determine leaf and unripe fruit resistance of Iranian promising walnut genotypes in response to controlled inoculation with X. arboricola pv. juglandis in orchard and laboratory conditions.Material and Methods: In this research, the relative resistance of leaf and unripe fruits to bacterial blight were studied in a number of promising walnut genotypes replicated during two years of 2015 and 2016. The local genotypes have been selected through massive surveys of native orchards in different provinces of the country. The main selective criterion for walnut selection was late leafing trait. In addition, correlation between leaf blight and unripe fruit blight severities were studied. The material included H17, H21, SHK2, Vina, Round de montignac (RDM), Lara, G4, G5, B10 and K15 genotypes and cultivars. From this material, KZ3, 882, 881 and G3 were registered and released in year 2019. Also, Serr, Chandler and Hartley cvs. were used as controls. A mixture of four local bacterial isolates originated from Qazvin, Karaj, Zanjan and Urmie was used as inoculum. The bacterial strains have already been characterized using different phenotypical and molecular tests. They were cultured on Nutrient Agar (NA) plates at 28 ℃. After 72 hours of cultivation, the colonies were suspended in distilled water; the concentration of the suspensions was read by spectrophotometer and after equalization, mixed and used as inoculum. Assessing leaf resistance was performed by spraying one year old grafted seedlings in glasshouse condition and lesion area was recorded 21 days after inoculation. Three leaves (contacting leaflets) of three seedlings were used per genotype. Assessing unripe fruit resistance was achieved by inoculating 45 days old fruits in laboratory condition and lesion diameter data was read 15 days after inoculation. 15 fruits per genotype were used and three lesions were created in each fruit. Statistical analysis of data was performed by Duncan Multiple test range using SAS software. Result and Discussion: Based on the results, leaf and unripe fruit blight severities were different among different cultivars and genotypes in both years of evaluation. Combined analysis of blight severity data indicated that G3 (Alvand) and 882 (Persian) genotypes had the most leaf blight severity and thus, rated as the most susceptible, while Hartley cultivar had the least leaf blight severity and thus, as the most resistant. Based on combined analysis of data, H11 and SHK2 genotypes had the most blight diameters of unripe fruits and thus rated as the most susceptible and resistant genotypes, respectively. Leaves of newly released cultivars of Persian, Caspian, Alvand and Chaldoran were rated as susceptible, relatively resistant, susceptible and relatively susceptible, respectively. On the other hand, unripe fruits of Persian, Caspian, Alvand and Chaldoran were classified as resistant, resistant, relatively resistant and susceptible, respectively. Mean leaf blight severities were not different between the two years of study and also there was no difference between unripe fruit severities between two years of the experiment. No significant correlation was found between leaf blight and unripe fruit blight severities.