Co-Authors:
Lisker, N., Dept. of Agronomy and Nat. Resources, Volcani Centre, Bet Dagan 50250, Israel
Keren-Shacham, Z., Dept. Postharvest Sci. Fresh Produce, Volcani Centre, Bet Dagan 50250, Israel
Sarig, P., Dept. Postharvest Sci. Fresh Produce, Volcani Centre, Bet Dagan 50250, Israel
Zutkhi, Y., Dept. Postharvest Sci. Fresh Produce, Volcani Centre, Bet Dagan 50250, Israel
Ben-Arie, R., Dept. Postharvest Sci. Fresh Produce, Volcani Centre, Bet Dagan 50250, Israel
Abstract:
Rhizopus stolonifer causes severe losses to Israeli grape exports. The fungus develops on mature berries in the field, during storage at temperatures above 0°C and during shelf-life. It was isolated from naturally contaminated soils throughout the year, and from fruits after mid-June. The airborne spore population increased in vineyards at the time of fruit maturation and was related to the proximity of stone-fruit orchards. The size of this population was highly correlated with disease incidence and thus may be a satisfactory tool for disease prediction. Intact young berries were more resistant than mature ones to Rhizopus inoculation, in both the vineyard and in the laboratory. Mechanical wounding, or chloroform dips, dramatically increased the susceptibility of young berries. The decline in acidity and the increase in the soluble solids content during growth and maturation of the berry were accompanied by an increase in susceptibility to inoculation. Scanning electron microscopy showed the fruit surface to be covered with white amorphous structures. At higher magnifications small cracks (approximately 1 μm in length) were observed on the surface but in no case was fungal penetration noticed through these cracks. In artificially inoculated fruits the fungus germinated near the wound and developed vigorously inside and around the fissure, producing sporangia. The young sporangium is covered by a smooth external layer which is compressed against the sporangiospores. After lysis of the cover, the young hexagonal sporangiospores can be observed. With maturation, the columella collapses and the mature sporangiospores are dispersed. In naturally infected berries, an important path for fungal penetration is the incomplete connection between the berry and the pedicle. Heavily infested berries become disconnected from their pedicles. Two chemicals applied to the surrounding atmosphere, orthophenyl phenate (as a fog) and calcium hypochlorite (as chlorine vapour), significantly decreased postharvest decay in artificially inoculated berries.
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