Incidence and severity of symptoms assigned to fraxinus excelsior bacterial disease in the left-bank forest steppe of Ukraine

Abstract

The aim of the research was to estimate the spread of bacterial disease on European ash (Fraxinus excelsior L.), ocularly estimated by lens-shaped blisters, swellings and cracks of the bark in Pridonetsky and Vorskla-Pselsky forest typological sector of the Left-bank Forest-Steppe zone of Ukraine. Studies were carried out in the year 2018 at 112 sample plots in Trostyanetske Forest Enterprise of Sumy region (Vorskla-Pselsky forest typological sector), Chugujevo-Babchanske and Skrypayivske Forest Enterprises of Kharkiv region (Pridonetsky forest typological sector). In spite of the fact that both the incidence and severity of ash bacterial disease symptoms are significantly higher for particular forestries and pooled data from Sumy region, the health condition index (HCI) of ash trees is greater for forestries of Kharkiv region. Therefore, ash stands in the inspected forestries of Sumy region are weakened, and in those of Kharkiv region are severely weakened. Ash tree mortality was rather low in them. The highest ash mortality was registered in Krasnyanske forestry (12.1%) of Trostyanetsky forest enterprise. No significant correlation was proved between parameters of ash bacterial disease and altitude. Significant correlation was proved between the incidence and severity of ash bacterial disease symptoms, health condition index and mortality, diameter at breast height (DBH) and disease severity. However, only the correlation of incidence and severity of ash bacterial disease symptoms is high for Kharkiv region (rp=0.74, rs=0.95) and moderate (rp=0.54) or high (rs=0.73) for Sumy region. Obtained distinction in ash disease incidence and severity in different forest typological sectors data may be explained by climate features. Higher precipitation and moisture indices in Vorskla-Pselsky forest typological sector is favorable for ash bacterial disease. However, higher temperature together with lower humidity in Pridonetsky forest typological sector are unfavorable to ash and increases its susceptibility to other damage causes, particularly frost and insects.