Pathogen resistance in aerial tubers of potato cultivars

Abstract

Increases in resistance of aerial tubers (cultivars Désirée, Epicure and King Edward) against nine pathogenic potato fungi were determined in vitro using freeze‐dried powder derived from subterranean and aerial tubers as a culture medium, and in vivo by inoculating both tuber types with the storage pathogens Fusarium sulphureum,F. solani var. coeruleum,Phoma exigua var. foveata and Polyscytalum pustulans. Significantly reduced growth rates and spore and conidiophore numbers were recorded when pathogens were cultured on freeze‐dried powder derived from aerial tubers. No effects on spore size of F. solani var. coeruleum were recorded but spore and conidiophore lengths of remaining pathogens were reduced and width increased, except for Colletotrichum coccodes, where the diameter of acervuli increased, and P. exigua var. foveata, where spore length and width were reduced. Reduced disease incidence, severity and spore numbers were recorded on aerial compared with subterranean tubers inoculated in vivo with the four storage pathogens. Spore length of P. pustulans was reduced and spore width increased, while spore length and width of P. exigua var. foveata were reduced on aerial compared with subterranean tubers inoculated with these pathogens. No effects on spore size of Fusarium spp. were recorded. Concentrations of glycoalkaloids, chlorogenic acid, calcium and magnesium were higher in aerial than in subterranean tuber tissue, which may have contributed to increased resistance and effects on size and morphology of fungal spores. The implications of using aerial tubers as an alternative technique for the production of seed potatoes and their importance to the potato industry are discussed.