عنوان مقاله [English]
Podosphaera xanthii and Golovinomyces cichoracearum are the two main species causing powdery mildew on cucumber worldwide. Cucumber powdery mildew and the fungal species involved in this disease have poorly been studied in East Azerbaijan province of Iran. In the present study, 37 cucumber plant samples with powdery mildew symptoms were collected from Tabriz, Ahar, Sarab, Basmenj and Shabestar, from June till September 2007. All collected species were identified based on conidial and cleistothecial morphology (1,3). In total, 48 isolates were studied of which 37 (77%) were identified as G. cichoracearum and 11 (23 %) as P. xanthic. In order to determine the race of isolated species, a set of differential melon cultivars (Iran H, PMR5, PMR45, Vedrantais, Edisto47, Nantais oblog, Mr-1, PI124112, PI414723 and WMR29), were used to determine the race of species. After 15 days of inoculation, the races were determined based on presence or absence of symptoms on differential host. Pitrat chart was used to evaluate and score the results (7). Based on the results, from 37 isolates of G. cichoracearum, 26 isolates were determined at the race level and of these 19 isolates were identified as race 0 and 7 isolates were determined as race 1. Among 11 isolates of P. xanthii, 8 isolates were identified as race 0. However, for the remaining 11 isolates of G. cichoracearum and 3 of P. xanthii, results were not conclusive because of the overlap between the differential set of cultivars. Analysis of variance and mean comparison (P=5%) was performed by using MSTATC software. Resistance assessment of the differential lines to different isolates showed that “Iran H” with 15.17 % mean infection was determined as susceptible and “Edisto 47” with 1.56 % mean infection was determined as resistant to G. cichoracearum. MR-1, PMR 45, PI 414723 and Nantais oblog were completely resistant and no infection was observed when inoculated with G. cichoracearum. For the other species isolates, in comparison to Vedrantais (with 7.5 % mean infection) “Iran H” (with 15.72 % mean infection) was also determined as susceptible to P. xanthii. The other lines were not infected and were considered resistant to P. xanthii.