غربالگري ارقام خيار مقاوم به سفيدك پودري و بررسي مقايسه اي فلورسانس كلروفيل در ارقام حساس و مقاوم

Screening of Cucumber Cultivars Resistant to Powdery Mildew and Comparative Assessment of Chlorophyll Fluorescence in Resistant and Susceptible Cultivars

خيار يكي از اقتصادي ترين صيفي جات توليدي در ايران است كه به شدت توسط سفيدك پودري مورد هجوم قرار مي گيرد. يكي از موثرترين راه هاي كنترل اپيدمي اين بيماري شناسايي و كاربرد ژنوتيپ هاي مقاوم به بيماري است. در مطالعه حاضر تعداد ۲۳ رقم خيار گلخانه اي و مزرعه اي از نظر مقاومت به سفيدك پودري غربالگري شده و ارقام مقاوم بر اساس برآورد درصد شاخص بيماري (PDI) شناسايي شدند. در ادامه فلورسانس كلروفيل برگ در ۵ رقم از گروه هاي مقاوم، نيمه مقاوم و حساس برآورد و مورد تجزيه و تحليل قرار گرفت. بر اساس نتايج برآورد شاخص بيماري، اختلاف قابل ملاحظه اي از نظر مقاومت به اين بيماري در بين ارقام مشاهده شد به طوري كه در چهار گروه مقاوم، نيمه مقاوم، نيمه حساس و حساس دسته بندي شدند. دو رقم گلخانه اي CLE و Green Magic به ترتيب با شاخص بيماري ۷/۷۸ و ۸/۳۳ مقاوم ترين و دو رقم مزرعه اي Beit Alpha و SuperN۳ به ترتيب با شاخص بيماري ۳۱/۱۱ و ۳۱/۶۷ حساس ترين ارقام شناخته شدند. در تجزيه واريانس شاخص هاي فلورسانس كلروفيل، اثر بيماري بر ۳ شاخص فلورسانس حداقل (Fo)، فلورسانس متغير (Fv) و شاخص سرزندگي گياه (Fv/Fm) و اثر رقم بر شاخص Fo معني دار بود (۰/۰۱=P). همچنين مقايسه ميانگين شاخص هاي فوق كاهش معني دار كارايي فتوسنتز در ارقام حساس تحت تاثير آلودگي را نشان داد در حالي كه كارايي فتوسنتز در ارقام مقاوم كاملا پايدار بود. نتايج اين پژوهش براي كنترل سفيدك پودري خيار بدون استفاده از روش هاي شيميايي كاربرد داشته و همچنين درك بهتري از تاثير بيماري بر فتوسنتز در گياه خيار ارائه خواهد داد.

Introduction: Cucumber is one of the most important vegetables in Iran which is extensively affected by fungal pathogens. Powdery mildew caused by Sphaerotheca fuliginea is distributed in both field and greenhouse cucumber cultures in almost all environmental conditions worldwide. In addition to several methods used to control the disease e.g. chemical, biological, agronomic and integrative methods, identification and application of disease resistant germplasm is an effective and environmentally safe method for controlling the pathogen. Screening of the resistant and susceptible germplasm can be performed by disease index estimation by visual evaluation of disease symptoms as well as by monitoring the agronomic, metabolic, biochemical and physiological parameters such as leaf chlorophyll fluorescence emission alterations. In the present study, 23 cucumber cultivars were evaluated for resistance to cucurbits powdery mildew caused by S. fuliginea using visual assessment of disease symptoms and five cultivars assigned as resistant, tolerant and susceptible genotypes were further assessed in terms of leaf chlorophyll fluorescence emission and related photosynthesis parameters. Materials and Methods: Cucumber cultivars were grown in plastic pots in three replicates in controlled environmental condition. The foliar spray method was employed for plant inoculation using S. fuliginea inoculum suspension prepared from freshly sporulating leaves. Disease evaluation and measurements were started I 0 days after inoculation and continued for 20 days, and the means of the three measurements were used for each replication for percent disease index (PDI) calculation for each cultivar. The cultivars were then compared, classified and screened for resistance to the pathogen based on the PDI results. For assessing the effect of infection on photosynthesis apparatus, five cultivars were chosen as resistant, semi-resistant and susceptible groups and were further studied by measuring leaf chlorophyll fluorescence and the related parameters including minimal fluorescence (Fo), maximal fluorescence (Fm), variable fluorescence (Fv), maximum photochemical quantum yield of PS II (Fv/Fm), Quantum yield of photochemical energy conversion in PS II [Y(II)], Quantum yield of regulated non-photochemical energy loss in PS II [Y(NPQ)], Quantum yield of non-regulated non-photochemical energy loss in PS II [Y(NO) and non-photochemical Chlorophyll fluorescence quenching (NPQ). The data were analyzed using MS-Exce/20 13 and SAS 19. I software. Results and Discussion: Based on the results of PDI measurements, the cultivars were grouped into resistant, semi-resistant or tolerant, semi-susceptible and susceptible. Two highly resistant cultivars i.e. CLE and Green Magic were identified with PDis of 7.78 and 8.33, respectively both belonging to greenhouse cultivars. This is while most of the field cultivars were among susceptible and semi-susceptible groups and none was resistant. The two highly susceptible cultivars Super N3 and Beit Alpha with POls of 31.67 and 31.11, respectively, were also belonged to field cultivars. The two highly resistant cultivars CLE and Green Magic comparatively showed less damage at later growth stages and no considerable damages were observed at the upper parts including leaves, stems, and fruits. The results of the chlorophyll fluorescence emission of five cultivars indicated that the infection significantly affected three chlorophyll fluorescence parameters including; minimal fluorescence (Fo), variable fluorescence (Fv) and vitality index i.e. maximum quantum yield of photosystem II (Fv/Fm) (P