The Spread of Dead-Arm Disease on Grapevine Caused by Phomopsis viticola in Southern Syria and its Correlation with the Prevailing Climatic Conditions

This study was conducted in the vineyards of southern Syria (Sweida Governorate), with the objective to estimate the spread of the dead-arm disease on the grapevine, its incidence and its relationship to the prevailing climatic conditions. 130 samples were collected during three seasons (2020, 2021 and 2022) from vines that showed visible symptoms of infection, in various grapevine growth stages, to be examined in the laboratory, and to isolate the pathogen. The results obtained showed the presence of the fungus Phomopsis viticola, which causes dead-arm disease on grapevine in 70% of the examined samples. The disease prevalence in the vineyards was in the range of 2 – 30 %, depending on the different sites surveyed, whereas the disease incidence in the studied vineyards ranged between 10 and 70%. Disease severity ranged between 1 and 3 based on a 0-3 scale. There was a positive correlation between the altitude above sea level and rainfall on one hand, and disease incidence and severity on the other hand, especially at the beginning of the spring season during bud-growth and after flowering. A negative correlation was obtained between temperature and disease incidence and severity, as the disease was not observed in areas with an altitude of less than 1200 m. Accordingly, the disease incidence varied among the three seasons, as the highest incidence was recorded during the 2020 season, with an average rainfall exceeding 600 mm during the spring season, and an average temperature of 18.1 °C. To the best of our knowledge, this is the first record of dead-arm disease on grapevine in Syria. Keywords: Grapevine, dead-arm, Phomopsis viticola, climatic conditions, first record.