Bacterial blotch of melons caused by strains of Acidovorax avenae subsp citrulli

The watermelon fruit blotch organism (Acidovorax avenae subsp. citrulli) wa s confirmed as the cause of a bacterial disease of rockmelon seedlings in J anuary 1996. Further outbreaks occurred in commercial nurseries during 1996 -98. An associated field disease was not observed in rockmelon and honeydew crops until May 1998 when wet conditions led to severe leaf spotting and f ruit infection in many crops in the Burdekin district of North Queensland. Isolates of A. avenae subsp. citrulli originating from these outbreaks were considerably more pathogenic to rockmelon plants than isolates originating from watermelon crops in South Queensland. They were also less pathogenic to the weed host Cucumis myriocarpus and could constitute new strains of th e fruit blotch organism. Tests showed the disease was readily seed transmis sible from naturally infected rockmelon and honeydew fruit for at least 3 m onths after seed extraction.