PHOMA MACDONALDIL ارزيابي مقاومت چند رقم آفتاب گردان به بيماري ساق سياه

Assessment of resistance of some sunflower cultivars to black stem disease (Phoma macdonaldii)

Black stem disease caused by Phoma macdonaldii is one of the most important diseases of sunflower. Development of resistant cultivars is one of the useful approaches to control this disease. For this purpose, reaction of 10 sunflower cultivars to the disease was studied in controlled environmental conditions in growth chamber using a randomized complete block design with 3 replications, (each replication consisted of 10 seedlings). "I welve days-old seedlings were inoculated with pycniospore suspension of Phama macdonaldii (10° pycniospore/ml). Ten days after inoculation, the two cotyledon petioles of each seedling were scored on a 1 to 9 rating scale for the percentage of necrosis on petiole area. The most tolerant cultivars were DK3825 and Argos (scored 4 and 4.4 respectively) and the most susceptible cultivar was Andora (scored 8.70). For comparison of the resistance of cultivars at the seedling and adult plant stages, two other experiments were carried out on four cultivars (resistant and susceptible) at the fifth pair leaves and flowering stages under the saute conditions. In both growth stages, the classification of cultivars at the seedling stage was confirmed. Positive and significant correlations between the reaction of cultivars at the fifth pair leaves (r =0.97) and flowering stage (r =0.99) were observed.