Influence of Leafroll Virus on Composition of Burger Fruits

Abstract

Levels of the principal organic acids, amino acids, and cations in fruits from healthy and leafroll-infected Burger vines, grafted onto Dogridge rootstock free of all known virus, were compared during the 1973 and 1974 seasons in a field trial at Davis. Total titratable acidity, and malate and tartrate, were significantly greater (P<0.01) in fruits from leafroll-infected vines than in fruits from healthy vines, when compared on the same sampling date. Potassium, too, was significantly higher in fruits from leafroll-infected vines during the entire ripening period (August 19 to November 1). High correlations existed between potassium and total acidity, malate, and tartrate, indicating that the higher levels of these organic substances in infected fruits may have been due to the increased amounts of potassium in the fruits. The concentration of proline in fruits from infected vines followed the levels of soluble solids, and was significantly less (P<0.05) than in healthy vines at all stages of fruit development. Arginine also was present in higher amounts in healthy fruits, compared to infected fruits, during early stages of fruit ripening. However, at the end of the ripening season, there was either no difference in arginine concentration of fruits, or infected fruits had somewhat higher arginine than did healthy fruits. Fruits from healthy or infected, cluster-thinned vines had higher levels of soluble solids, arginine, and proline than did fruits from vines with full crops. In contrast, concentrations of total acidity, tartrate, malate, and potassium were not significantly affected by crop level when compared on the same sampling date.