Insights Into the Etiology of Gummosis Syndrome of Deciduous Fruit Trees in Israel and its Impact on Tree Productivity.

Fungal gummosis syndrome of deciduous fruit trees was reported from several countries, including Israel. Symptomatic 5-7 to 10-14-year-old trees exude large amounts of gum on the trunk, limbs, branches, and twigs, accompanied by sunken lesions on the bark. The necrotic area extends to the xylem to form black to brown staining of the tissue. The general conception is that "this is a nuisance that can be pruned out of trees during the dormant season with no economic significance." In this study we attempted to: (i) identify the fungi associated in the gummosis syndrome of deciduous trees in Israel and (ii) quantify the significance of gummosis syndrome on tree and fruit development and on crop value. Branches from symptomatic and asymptomatic deciduous trees were collected during 2012 to 2015 from 29 orchards including peach (14 orchards), nectarine (six orchards), apricot (six orchards), plum, cherry, and almond (one orchard each). In all cases, fungi associated with the Botryosphaeriaceae family were isolated from tissues exhibiting the typical gummosis symptoms. The decay fungus Phellinus sp. was isolated from 53.3% of the samples. The dynamics of fruit growth in symptomatic and asymptomatic trees was recorded in 2014 and 2015 in an 11-year-old peach orchard. In trees exhibiting the gummosis syndrome, yield was lower by 11.5 to 22.5% and its value was reduced by 14.7 to 19.4%, compared with those of asymptomatic trees in 2014 and 2015, respectively. Although these are substantial losses, the grower of the orchard was not aware of the losses occurring in his orchard. The reason for this situation is explained and discussed. The outcome conclusion of the current study is that the gummosis syndrome of deciduous trees imposes significant, hence undistinguishable, losses in mature deciduous fruit trees.