The role of calcium concentration in the endocarp wall of apple fruit in the development of core rot

摘要

Core rot in 'Red Delicious' apples, induced by Alternaria alternata, is responsible for significant economic losses in Israel, among other regions. It was previously reported that the pathogen colonizes the loculus (the ovary or seed cavity) of most fruits in Israel. Our working hypothesis was that invasion of A. alternata mycelium colonizing the loculus into the mesoderm (flesh) of apple fruit is governed by the calcium (Ca) concentration in the loculus wall (endocarp): low Ca concentration facilitates pathogen invasion and results in the development of core rot and high Ca concentration precludes the invasion, containing the pathogen in the loculus. The specific objectives of this study were to (i) quantify the relationship between Ca concentration in the endocarp wall and core rot incidence; and (ii) evaluate the effect of means aimed at increasing Ca concentration in the endocarp wall as a tool for core rot suppression. Eight experiments were carried out between 2012 and 2015 in commercial apple groves in northern Israel. The results suggested that high core rot incidence is associated with low Ca concentration in the endocarp wall and vice versa, supporting our working hypothesis. However, our attempts to increase Ca concentration in the endocarp wall by diverting Ca transport from the leaves to the developing fruit and by applying commercial products containing Ca directly to the developing fruit were unsuccessful. Thus, the validity of this approach for suppression of core rot incidence could not be verified.