EVALUATION OF GRAPE ROOTSTOCKS FOR RESISTANCE TO PIERCE'S DISEASE AND ADAPTATION TO NORTH FLORIDA ENVIRONMENT

To understand the adaptation of grape rootstocks commonly used in major grape production areas worldwide to Florida, where the growing season is hot and humid that favors the prevalence of Pierce’s Disease (PD), ten major grape rootstocks were evaluated for their PD resistance and growing performance at the experimental vineyard, Florida A&M University, Tallahassee, Florida. Leaf necrosis of Pierce’s disease was observed among all the rootstocks tested, but severity varied. ‘Ramsey’, ‘St George’, ‘5C’ and ‘110R’ demonstrated relatively light PD symptoms, while ‘Freedom’, ‘3309C’ and ‘O39-16’ showed high PD scores. Significant variations of vine survival rate were observed in the 3^rd growing season when ‘Freedom’, ‘3309C’ and ‘O39-16’ lost more than 50% of their original vines. In the mid-6^th growing season, only four rootstocks had more than 70% vines alive, with 100% survival of ‘Ramsey’ rootstocks. Vine vigor was evaluated from 2002 to 2005, and varied among the rootstocks when assessed by trunk diameter, annual shoot length, annual shoot node number, and shoot diameter. The overall growth performance suggested that ‘Freedom’, ‘3309C’, ‘44-53M’, ‘101-14MGT’ and ‘5BB’ could not endure the North Florida environmental conditions.