Susceptibility of some apple cultivars to infestation by the rosy apple aphid [Dysaphis plantaginea Pass., Homoptera: Aphididae]

Abstract

Gums are induced by infection, insect attack, mechanical and chemical injury, water stress, and other environmental stressors in some plant species. All of these factors are believed to act via ethylene produced in plant tissues. Ethylene is believed to be the main factor responsible for the induction of gummosis. Ethylene or ethylene-releasing compounds such as ethephon (2-chloroethyl-phosphonic acid) substantially stimulate gum formation in stone-fruit trees and their fruits of the Rosaceae family, such as cherries, ornamental Japanese cherries, plums, apricots, peaches and almonds. Gums consist mostly of polysaccharides, although they contain several other substances as well. Biotic and abiotic stressors cause a rapid increase in the level of endogenous jasmonates, mainly jasmonic acid (JA). Jasmonates are a new group of plant hormones. Infection, insect attack, mechanical wounding and other stresses induce ethylene production in plant tissues. Jasmonates exogenously applied to plant tissues also stimulate ethylene production. Jasmonates substantially induces gummosis in cherries, plums, peaches and apricots. In this review, the ways in which ethylene and jasmonates act and the pathways of gum biosynthesis are discussed.