INGRESS OF THE WATERMELON FRUIT BLOTCH BACTERIUM INTO FRUIT

Bacteria were observed with the scanning electron microscope to be located randomly on watermelon (Citrullus lanatus) fruit surfaces 2 hr after inoculation with drops of suspensions of the fruit blotch bacterium. For the next 4 days, bacteria were observed around and in stomata. Nine days after inoculation, masses of rod-shaped bacteria were observed in stomatal chambers. The incidence of disease decreased with age of the fruit at the time of inoculation. The incidence of plugging, or covering, of stomata in the fruit with wax progressively increased with fruit age and appeared to provide a morphological barrier to bacterial ingress. The observations were consistent with the concept that the pathogen enters the fruit through stomata and that immature fruit are the most likely to be infected.