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Poster: Biology & Disease Mgmt: Bacteriology


Further evidence for host preference among Acidovorax citrulli strains based on a detached melon fruit assay
L. YAN (1), R. Walcott (2), B. Hu (1) (1) Nanjing Agricultural University, China; (2) University of Georgia, U.S.A.

Bacterial fruit blotch (BFB), caused by Acidovorax citrulli, is a serious threat to cucurbit crop production. A. citrulli strains can be divided into two genetically distinct groups with group I strains being associated with a range of cucurbits and group II strains being associated with watermelon. Despite this, seedling pathogenicity assays for A. citrulli lack the sensitivity to distinguish the groups. In this study, we developed an immature, detached melon (cv. Joaquin Gold) fruit assay that clearly distinguished the two A. citrulli groups. We observed that four group I strains induced typical water-soaked lesions on melon fruit rind tissue 7 to 10 days after pin-prick inoculation. In contrast, four group II strains did not induce symptoms on detached melon fruits. Additionally, a type III secretion (T3S) system mutant of the group I strain, M6 (M6?hrcV), failed to induce watersoaking in the same assay. Based on these observations, we conclude that group I A. citrulli strains have the capacity to infect immature melon cv. Joaquin Gold fruit, while group II strains do not. The difference in the ability of group I and group II A. citrulli strains to induce watersoaking on immature melon fruit is determined by T3S effectors. Further investigation using this detached melon fruit assay will help to identify the A. citrulli T3S effectors responsible for this differential pathogenicity phenotype.