Viticultural Traits of Three Pierce's Disease-resistant Vitis vinifera L. Selections in Alabama

Vitis vinifera grape production in the southeastern United States is limited by the endemic bacterium, Xylella fastidiosa, causal agent of Pierce’s Disease (PD). V. vinifera selections bred at the UC Davis: ‘501-12’, ‘502-01’, and ‘502-10,’ all grafted on ‘Dog Ridge’ rootstock, were planted in 2010 at the Chilton Research and Extension Center to evaluate their growth and performance in the high PD pressure conditions of Alabama. PD infection was not detected during vineyard establishment; as a result, each selection’s viticultural characteristics were recorded throughout the 2015 and 2016 growing seasons to further understand the attributes of V. vinifera grown in central Alabama’s humid subtropical climate, averaging over 130 cm in annual precipitation. Vine vigor was notable in all three selections as characterized by dormant pruning weights and trunk cross sectional area (TCSA). In 2016, TCSA was greatest for ‘502-01’ (188.7 cm²).  In both 2015 and 2016 ‘501-12’ had the smallest TCSA. Ravaz index based on the 2015 crop and 2016 pruning weights indicated differences between selections; ‘501-12’ had the smallest Ravaz index at 3.1 while selections ‘502-01’ and ‘502-10’ both had a Ravaz index of 4.5.  All tested selections were slightly below the recommended Ravaz index ranges for V. vinifera cultivars. Dormant pruning weights revealed high vigor for all selections. ‘501-12’ had the highest pruning weight of 2.9 kg/vine, followed by ‘502-01’ and ‘502-10’ with similar pruning weights of 2.4 kg/vine and 2.5 kg/vine, respectively. As V. vinifera selections become a commercially available planting option for southeastern vineyards, it will be increasingly important to further refine concepts of vine balance and vigor to enable development of economically and environmentally sustainable management techniques in the southeastern region.