EVALUATION OF LIKELIHOOD OF CO-OCCURRENCE OF ERWINIA AMYLOVORA WITH MATURE FRUIT OF WINTER PEAR

T.N. Temple, V.O. Stockwell, K.B. Johnson, P.L. Pusey
Over a four year period, we evaluated the potential for co-occurrence of E. amylovora with mature symptomless winter pear fruit by inoculation experiments and by survey of commercial orchards. Immature pear and apple fruit were inoculated in orchards with E. amylovora strain 153N as resuspended, lyophilized cells or ooze from diseased tissues. Regardless of inoculum type, populations of Ea153N on fruit declined by an order of magnitude every 3 to 4 days during the first two weeks after inoculation; at 56 days after inoculation, Ea153N was not detected except on 1 of 450 fruit with 4 CFU. After inoculation of flowers, calyx end survival of Ea153N on pear and apple fruit declined from high populations at petal fall to a few cells at harvest, with no detection of the pathogen after a 7-week cold storage. The potential for migration of Ea153N into symptomless pear fruit from blighted branches was evaluated by enrichment assay and nested PCR of internal fruit core tissues; these assays failed to detect the pathogen in healthy fruit from diseased trees. In harvest surveys, E. amylovora was not detected on 5599 of 5600 fruit of ‘d’Anjou’ pear sampled from orchards located in major production areas of the Pacific Northwest; one fruit yielded 32 CFU of the pathogen. In postharvest experiments, mature fruit contaminated with Ea153N and subsequently wounded required a dose of >10,000 cells at the wound site to allow for persistence of the pathogen through a 7-week cold storage. We conclude that epiphytic E. amylovora has similar survival characteristics on both pear and apple fruit, that it is not endophytic within mature symptomless pear fruit, its presence is exceptionally rare on commercially-produced fruit, and that epiphytic survival of E. amylovora through a postharvest chilling period is unlikely given the unrealistically high population size required for persistence.
Temple, T.N., Stockwell, V.O., Johnson, K.B. and Pusey, P.L. (2008). EVALUATION OF LIKELIHOOD OF CO-OCCURRENCE OF ERWINIA AMYLOVORA WITH MATURE FRUIT OF WINTER PEAR. Acta Hortic. 793, 73-81
DOI: 10.17660/ActaHortic.2008.793.7
https://doi.org/10.17660/ActaHortic.2008.793.7
phytosanitary risk assessment, phyllosphere microbiology, exotic pest quarantine
English

Acta Horticulturae