Abstract
Pierce's disease (PD) is the greatest threat to the production of grapes in southeastern United States. PD infected leaves show various abnormalities with symptoms similar to mineral nutrient imbalances such as deficiencies and toxicities. A study was initialed to investigate the roles of macronutrients including calcium (Ca[sup+][sup+]), potassium (K[sup+]), and magnesium (Mg[sup+][sup+]) in PD development of grapevines. Symptomatic and asymptomatic leaves were collected from naturally Xylella fastidiosa infected field-grown grapevines for the Vitis rotundifolia cultivar 'Carlos' and hybrid 'Blanc du Bois' and 'Blue Lake'. The concentration of nutrients was measured by Inductively Coupled Plasma (ICP) emission spectrometry. 'Carlos' had an average level of 1.83, 0.98, and 0.27% of Ca[sup+][sup+], K[sup+], and Mg[sup+][sup+]in leaf tissue. The hybrid 'Blanc du Bois' had an average level of 2.79, 1.16, and 0.44% of Ca[sup+][sup+], K[sup+], and Mg[sup+][sup+], respectively. High levels of Ca[sup+][sup+]and Mg[sup+][sup+]but low levels of K[sup+]were found associated with PD-infection. In addition, most of the nutrients were located in petioles rather than in leaf blades. These results indicate that leaf petioles can be a better indicator for plant nutrient analysis related to PD development in grapevines.
