واکنش هیبریدهای امیدبخش گردو به بیماری لکه سیاه (ophiognomonia leptostyla)

بیماری لکه سیاه گردو (ophiognomonia leptostyla)، یکی از مهمترین بیماری‌های برگی این محصول در اغلب مناطق گردوکاری است. در این پژوهش، واکنش نهال‌های پیوندی چهار هیبرید امیدبخش و پرمحصول گردو (h 1-7, h 2-1, h 1-1, h 2-12) به همراه رقم هارتلی (hartley) و ژنوتیپ k72 به‌ترتیب به عنوان شاهد مقاوم و حساس، در برابر قارچ عامل بیماری مورد بررسی قرار گرفت. آزمایش به صورت فاکتوریل در قالب طرح کاملا تصادفی با سه تکرار و دو عامل جدایه قارچی (در دو سطح) و ارقام و ژنوتیپ‌های گردو (در 6 سطح) انجام شد. در بهار 1400 و 1401 نهال‌های گردو با استفاده از سوسپانسیون کنیدی قارچ با غلظت 105 اسپور در میلی‌لیتر مایه‌زنی شدند. تعداد و قطر لکه‌های نکروز، در سه نوبت به فواصل 15 روز یادداشت‌برداری شد. نتایج نشان داد که 45 روز پس از مایه‌زنی، بیشترین تعداد لکه به هیبرید h 2-12 تعلق داشت. همچنین بزرگترین لکه‌های بیماری روی هیبریدهای h 1-1 و h 1-7 مشاهده شد. اولین آسروول‌ها، 44-43 روز پس از مایه‌زنی، بر روی ژنوتیپ‌های h 1-1 و h 2-12 ظاهر شدند. کلیه‌ی ژنوتیپ‌ها در برابر بیماری حساس بودند، اما شدت بیماری در آنها متفاوت بود. میانگین سطح آلوده برگچه‌ها (nla) در دامنه‌ای از 20 (در هارتلی) تا 90 درصد (در h 1-7) متغیر بود. براساس درصد سطح نکروز برگچه‌ها، هیبریدهای h 1-1, h 1-7 و h 2-12 به همراه k72 در گروه فوق حساس، و هیبرید h 2-1 با میانگین 52 درصد آلودگی در گروه نیمه‌حساس طبقه‌بندی شدند. هارتلی نیز میزان اندکی از آلودگی را نشان داد.

reaction of promising walnut hybrids to black spot disease (ophiognomonia leptostyla)

black spot disease (ophiognomonia leptostyla) is an important disease in walnut growing areas all over the world. four promising walnut hybrids; h 1-1, h 1-7, h 2-12 and h 2-1 were evaluated for susceptibility to using factorial arrangement in completely randomized design. hartley and k72 were included as resistant and susceptible controls, respectively. the experiment was conducted in spring 2021 and 2022. fully expanded walnut leaflets were inoculated by fungal conidia (105 spore ml-1). number and size of necrotic spots were recorded at 15-day intervals until 45 days after inoculation. according to the data of 45 days after inoculation, the maximum number of necrotic spots belonged to h 2-12 while the largest spots were developed on h 1-1 and h 1-7. first acervuli appearance was occurred 43-44 days after inoculation on h 1-1 and h 2-12. all evaluated hybrids were susceptible, but symptoms development and disease severity varied. the average of nla ranged from 20% in hartley to 90% in h 1-7. h 1-7, h 1-1 and h 2-12 as well as k72 exhibited high level of infection and was considered as highly susceptible. hybrid h 2-1 with the average nla of 52% was classified in moderately susceptible group. keywords: walnut, inoculation, necrosis, necrotic leaflet area, resistance. introductionblack spot disease caused by the fungus ophiognomonia leptostyla (fr.) sogonov is one of the most important foliar diseases of walnut tree that affect its fruit production and nut quality worldwide. the fungus mostly attacks leaves, petioles, young shoots and fruits after prolonged periods of wetness. irregular circle brown and black spots occur on plant tissues led to premature defoliation and fruit drop. primary spots provide conidia that spread by wind and water splashing and cause secondary infections in walnut orchards. trees may become weak by reduction of fruit yield and nut quality. using resistant cultivars could be integrated with other control measures such as orchard management practices and chemical fungicides to manage and control the black spot disease. several studies have shown variation in walnut cultivars for susceptibility to black spot disease (arnaudov et al., 2014; dastjerdi and hassani, 2009; jelev and marinov, 2018). studies in iran have shown that cv. jamal, cv. damavand and cv. persia are slightly susceptible, very low susceptible, and moderately resistant to black spot disease, respectively (dastjerdi and hassani, 2009; dastjerdi et al., 2023).the promising walnut hybrids used in this research have been developed in the national walnut breeding program with the aim of obtaining new cultivars that are suitable for planting in different walnut-growing areas of iran. the objective of this study was to determine their reaction of four paromising walnut hybrids to o. leptostyla. material and methodsreaction of four promising walnut hybrids; h 1-7, h 2-1, h 1-1, h 2-1) to o. leptostyla was assessed in greenhouse conditions during spring 2021 and 2022. hartley and k72 were considered as resistant and susceptible control, respectively. the purified culture of two fungal isolates; q57 and la were used for inocultion. the experiment was conducted as factorial arrangements in completely randomized design with six replications. experimental treatments were combination of two factors including; cultivars (6 levels) and fungal isolates (2 levels). fully expanded leaflets of grafted plants were inoculated by fungal conidia (105 spore ml-1). the number and size of necrotic spots were recorded in 15-day intervals, continued until 45 days after inoculation. due to the appearance of mature fruit bodies (acervuli) and starting of secondary disease cycles, data on the 45 days after inoculation was used for determination of susceptible genotypes. computation of leaflet area and infection area led to the determination of nla for each isolate/cultivar combination. data were inserted in excel ver. 2013 and the graphs were using excel software. results and discussionthe first macroscopic symptoms appeared 8-10 days after inoculation as small brown spots with gray halos first on the lower surface of the leaves of h 2-12, in both years. the spots gradualy developed and formed larger necrotic spots. control plants, inoculated with distilled water, did not show any symptoms. the appearance of acervuli on h 1-1 in 2021 and h 2-12 in 2022, occurred 44 and 43 days after inoculation, respectively.descriptive statistics of evaluated traits for susceptibility of promising walnut hybrids to black spot disease demonstrated that the percentage of nla ranged from 0.05-100 with the average of 67.5%. disease incidence was recorded on 82.3% of inoculated leaflets. it showed the successful establishment and spread of black spot disease, and penterationin the fungus in walnut tissues. considering the data of 45 days after inoculation, the maximum number of spots belonged to h 2-12 hybrid while the largest spots developed on h 1-1 and h 1-7 hybrids. the highest nla was recorded on h 1-7 hybrid.the evaluated promising hybrids were classified in two susceptibility groups. all evaluated walnut hybrids were susceptible, but symptoms development and disease severity varied among them. the average of nla ranged from 20% (in cv. hartley) to 90% (in h 1-7 hybrid). h 1-7, h 1-1 and h 2-12 hybrids demonstrated high level of infection, and therefore were grouped with k72 as highly susceptible group. the h 2-1 hybrid with the average nla of 52% was classified in moderately susceptible grouped. dastjerdi et al. (2023) reported the hartley exhibited very low level of susceptibility. susceptible cultivars/hybrids are not recomended for the hot spot area where the black spot disease is a serious problem for walnut growing and production. referencesarnaudov, v., gandev, s. and dimova, m. 2014. susceptibility of some walnut cultivars to gnomonia leptostyla and xanthomonas arboricola pv. juglandis in bulgaria. agro-knowledge journal, 15, pp.41-54. doi: 10.7251/agren1401041adastjerdi, r. and hassani, d. 2009. response of walnut genotypes to gnomonia leptostyla (fr.) ces. denote. in greenhouse. seed and plant, 25(3), pp.433-449 (in persian). doi: 10.22092/spij.2017.110992dastjerdi, r., hassani, d., nadi, s. and soleimani, a. 2023. response of some walnut genotypes (juglans regia l.) to anthracnose attack (ophiognomonia leptostyla). journal of agricultural science and technology, 25(5), pp.1207-1221. doi: 10.22034/jast.25.5.1193jelev, z. and marinov, m. 2018. reactions of organically grown walnut cultivars to walnut blight (xanthomonas compestris p.v. juglandis) and anthracnose (gnomonia leptostyla). pp. 188-190. in: proceedings of the 18th international conference on organic fruit-growing, hohenheim, germany.