Abstract
The survival of Acidovorax avenae subsp. citrulli (Aac) on watermelon seeds and the population dynamics of Aac on watermelon seedlings were examined. Aac survived for over 26 months on infested seeds that were stored at 4, 10, 15, 20 and 30°C. These infested seeds were then thought to become a source of infection. When infested seeds with only 1 cfu of Aac were sown and grown under high humidity, there was a high probability of the germinated seedlings becoming diseased. The percentage of diseased plants was higher under high humidity than low. When germinated seedlings were inoculated with Aac (105cfu/ml) by spray inoculation and then grown at high humidity, the population of Aac on watermelon seedlings reached 106-107cfu/g fresh weight from below 10cfu/g fresh weight and seedlings were diseased by 2 days after inoculation. When the inoculated seedlings were incubated at low humidity, Aac multiplied to 104-105cfu/g fresh weight on seedlings by 2 or 3 days. However, no seedlings were diseased. From the data obtained by different isolation methods, Aac grew mainly on the surfaces of the seedlings.
