Role of honey bees in watermelon seed infestation by Acidovorax avenue subsp. citrulli

Bacterial fruit blotch (BFB) caused by Acidovorax avenae subsp. citrulli (Aac) is a devastating seedborne disease of cucurbits. Hence, exclusion of infested seed is critical for BFB management. Female watermelon blossoms have been reported as an infection court for seed infestation by Aac suggesting a possible role for pollinating insects as Aac vectors. The objective of this work was to investigate the possible role of honey bees in watermelon seed infestation by Aac. In multi-year field experiments, honey bees that had been exposed to BFB-infected watermelons were incubated with uninfected plants at anthesis, under insect cages. Contaminated bees were allowed to pollinate blossoms and seed from mature fruits were tested for Aac. Negative controls consisted of fruits set and protected before honey bee introduction and from blossoms pollinated with non-contaminated bees. Aac was detected in 12.5% and 3.2% of seedlots from fruits exposed to contaminated bees and control fruits, respectively. Aac strains recovered from infested seedlots shared identical DNA fingerprints with the strains associated with the infected plants. These data suggest that honey bees can vector Aac to watermelon blossoms which leads to seed infestation under field conditions.