Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/1997
Publication Date: N/A
Interpretive Summary: Infection by green mold causes a predominant amount of citrus postharvest decay. Spores of this fungus are ubiquitous in citrus growing areas and in the fruit handling environment. Quarantines against the importation of fresh grapefruit from areas where fruit flies are endemic can restrict the movement of grapefruit in domestic and international markets. Heat is an effective method for controlling postharvest decay of fresh fruits and vegetables, however, heat treatments targeted specifically for controlling decay use a higher temperature and shorter exposure than what is required for quarantine security. This research investigates whether exposing grapefruit to moist, forced-air at 46C for the duration known to provide quarantine security against the Mexican fruit fly is also effective in reducing the growth of green mold. Grapefruit were inoculated with a spore suspension of a known concentration prior to or after heating. Control fruit were inoculated and not heated. Fruit inoculated prior to heating developed smaller lesions than fruit inoculated after heating. The lesion size of control fruit was similar to fruit inoculated after heating. Results suggested that moist, forced-air reduced the progression of decay via a non-residual, heat-induced inhibition of pathogen growth.
Technical Abstract: Lesions of grapefruit wound inoculated with a spore suspension of Penicillium digitatum just prior to heating for 300 min in 46C moist, forced-air developed less rapidly after 4 d of storage at 21C than lesions formed from inoculations made after the fruit was heated or lesions on non- heated fruit. Since the lesion size of fruit inoculated after heating was similar to fruit that were not heated, induced host resistance via lignification or accumulation of phytoalexins most likely did not occur. Protein synthesis is reported to be inhibited at the fruit surface temperature that was obtained during exposure to 46C moist, forced-air, further suggesting that mode of action was most likely attributed to a nonresidual, heat-induced inhibition of pathogen growth. Results from this research demonstrate that the progression of postharvest decay on grapefruit caused by green mold is inhibited by exposure to a temperature and duration of moist, forced-air known to provide quarantine security against Mexican fruit fly.