Combining quince (Cydonia oblonga) rootstock with soil-applied calcium chloride solution as a strategy to control brown spot (Stemphylium vesicarium) incidence in Abbe Fetel pear fruits

Brown spot (Stemphylium vesicarium) is a fungal disease widespread in European pear industry. The high number of fungicide applications required to control the disease can promote strains with fungicide resistance. The aim of the present study was to assess the effectiveness of soil-applied water solution of calcium chloride in combination with rootstock to control the incidence of brown spot in Abbe Fetel pear. Soil salinity, stem water and osmotic potential, along with fruit fraction of calcium and defence-mechanism related-enzymes such as peroxidase, polyphenol oxidase, phenyl-alanine ammonia-lyase, and beta-1,3-glucanase were investigate in tree grafted on Fox 11 (Pyrus communis L.) and Sydo (R), a quince (Cydonia oblonga) rootstock. Both grafting combinations were fertigated or not with calcium chloride. Sydo (R) showed a positive effect in reducing brown spot severity on Abbe Fetel. Compared to Fox 11, fruits from trees grafted on Sydo (R) showed higher calcium concentrations, fraction of calcium pectate, fruit firmness, polyphenol oxidase, phenylalanine ammonia-lyase and beta-1,3-glucanase levels. Fruit calcium concentration was positively correlated with disease fruit tolerance. However, soil calcium applications were ineffective in promoting fruit calcium partitioning. Calcium chloride applications decreased leaf osmotic and stem water potential in trees grafted onto Sydo (R), but this wasn't found in those grafted on Fox 11. In conclusion, Sydo (R) rootstock promoted Ca acquisition, osmotic adjustment at leaf and fruit level, fruit synthesis of defence-related enzymes that all together reduced brown spot severity in Abbe Fetel pear