Initiation and development of Erysiphe necator chasmothecia and their role in the epidemiology of grapevine powdery mildew in southern Syria

Abstract

Powdery mildew caused by Erysiphe necator is the most important fungal disease of grapevine in southern Syria. The purpose of this study was to determine the development of chasmothecia and their role as a primary inoculum in spring. Leaves and/or branches were examined by a stereo binocular from July to December 2014 and 2015. The number of chasmothecia was estimated on both surfaces of the leaves, and their viability was estimated by microscopic examination. During 2 years of survey chasmothecia were detected in 45.5% of vineyards. The initial development of chasmothecia on infected leaves was observed in the second half of July. Their numbers increased from July to October, and the sudden reduction at the beginning of November was noted. Chasmothecia were formed on 38.7% of infected leaves, with 12.5%, 18.4%, and 7.5% on the upper, under and on both surfaces of infected leaves respectively. Chasmothecia were more frequent on the leaf under side (0.6 / leaf) than on the leaf upper side (0.4 / leaf), but their occurrence on both sides together was relatively low (0.2 / leaf), and their numbers were highly variable between vineyards and years. Microscopic examination showed that chasmothecia contained 1-5 (usually three) asci with 1-4 (usually three) ascospores in each asci, and 65.6% of chasmothecia were empty. Their viability decreased between December and February, with an average viability of 1.2% and 0.2% in March and April, respectively. Chasmothecia were not detected on bark and ascospores were not trapped at the beginning of the season. These results indicate that the ascospores have no or little role in the initiation of spring infection. To the best of our knowledge, this is the first report of E. necator chasmothecia development and their role in the initiating infection on grapevine in Syria.

Survival and viability of ascospores of Erysiphe necator in Austrian vineyards

“…Only a small amount of chasmothecia originating from naturally overwintered leaf litter contained viable chasmothecia (maximum of 5%), Our result is in accordance with findings from New York, Italy and Syria, showing a maximum of 10% viable chasmothecia on overwintered leaves at bud break (Gadoury and Pearson 1988;Cortesi et al 1997;Hajjeh et al 2008;Alimad et al 2016). However, in Washington a percentage of 67% was observed on artificially overwintered leaf litter samples during this period (Grove 2004).…”

Detection of Erysiphe necator, the Causal Agent of Powdery Mildew on Grapevine, and Determination of their Mating Types in Southern Syria Using Some Molecular Markers

“…Environmental factors such as temperature, day length, humidity, leaf age and host resistance do not affect chasmothecia initiation and, once initiated, only temperature and host resistance affect their growth (Legler et al, 2013;Pearson & Gadoury, 1987). In Syria, chasmothecia were observed in 45.5% of studied vineyards (Alimad et al, 2016). E. necator has been reported to overwinter as mycelium in dormant buds and/or as chasmothecia on the bark of vines or in the soil (Cortesi et al, 2005 al.,2003).…”