ARS | Publication request: Microbial interactions affecting stem-end blue mold decay of 'd'Anjou pears

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 10, 2006
Publication Date: June 15, 2006
Citation: Janisiewicz, W.J. 2006. Microbial interactions affecting stem-end blue mold decay of 'd'Anjou pears. Postharvest Biology and Technology. 42(2006):217-221.

Interpretive Summary: Stem-end decay of 'd'Anjou' pears caused by blue mold and gray mold fungi is the major decay of fruit kept in cold storage for extended periods of time. The moist, thick stems of 'd'Anjou' pear can be easily colonized by these fungi which penetrate further to fleshy fruit tissue and cause decay. We isolated bacteria and yeasts from the surface of the pear and apple fruits, and evaluated them for ability to grow on pear stem. Some bacteria and yeasts increased more than 100 times during three days at room temperature. These were then evaluated in cold storage for their ability to protect pear stems against blue mold fungi. A few of them reduced blue mold decay of fruit; however two bacteria, Pseudomonas chlororaphis, and Enterobacter sp., were found to increase fungal infection of pear stem and subsequent fruit decay. The abundance of these decay-enhancing bacteria on pears in some years may be responsible for the high incidence of blue mold stem-end decay in those years.

Technical Abstract: Stem-end decay of 'd'Anjou'pears caused by Penicillium expansum or Botrytis cinerea is the major decay of fruit kept in cold storage for extended periods of time. The succulent thick stems of 'd'Anjou pear are prone to colonization by these fungi. We isolated bacteria and yeasts from the surface of pear and apple fruits and evaluated them for their ability to colonize pear stem tissue. Populations of the best bacterial and yeasts colonizers increased by more than 2 log units within 3 d at 24 degrees C. They were then evaluated in cold storage at 1 degree C for their ability to prevent infection of pear stems by a very aggressive strain of P. expansum, and a weakly pathogenic strain of a Penicillium sp. isolated from a pear stem. Only a few isolates reduced stem-end decay. Two bacteria, Pseudomonas chlororaphis and Enterobacter sp. promoted fungal infection of the stem and subsequent fruit decay. The abundance of decay promoting bacteria in some years may by responsible for the high incidence of stem-end decay in those years.