Sour rot of fig—various bacteria and yeasts
Causes of sour rot, or souring, include fruit infection by Candida, Hanseniaspora, Kloeckera, Pichia, Saccharomyces, and Torulopsis species of bacteria and yeasts.
Identification
When ripe fig fruit is fermented and sour, this can readily be detected by the fruit's sour odor, unpalatable flavor, and development of water-soaked lesions. Rancid fluid may drip from a tiny hole at the end of the fruit.
These symptoms of sour rot become noticeable only when the fruit ripens and the fig eye (ostiole, tip with a hole) opens. Infected figs develop a pink color. A thick, pink liquid exudes through the eye and becomes jellylike at the eye or drips on to leaves. Gas bubbles may be apparent in this ooze.
During later stages of disease development, the fig pulp disintegrates and commonly becomes covered by a white scum. The affected figs turn soft and black, sag, shrivel, dry up, and drop or remain hanging on the twig. A dead spot (eye canker) commonly develops in the bark around the attachment of the stem of affected fruit.
Symptoms of sour rot are more distinct on fruit cultivars that need no caprification (pollination), such as Adriatic figs. In cultivars needing caprification (e.g., Calimyrna), the symptoms of sour rot may be confused with the symptoms of fig endosepsis.
Lookalike. Fig endosepsis is caused by Fusarium species of fungi. With endosepsis, when fruit are green, a cross-section of either infected caprifigs or edible figs will show internal streaks of brown or pink. Areas on the base of flowers, or sometimes entire flowers become discolored brown. As figs ripen, the brown streaks become rusty colored spots affecting many flowers within the fig. Usually these colored spots are first found in the pulp near the eye of the fig, but they can develop on any part of the pulp. No external symptoms on fruit are noticeable at this stage of infection. But as figs with endosepsis soften with maturity, a circular area of skin, usually beginning around the eye, becomes water soaked in appearance. The water-soaked area eventually extends up the sides to the neck and turns purple. Unlike fig endosepsis, sour rot causes no browning of fig flowers.
Life cycle
The bacteria and yeast that cause sour rot can be common in soil and the growing environment. Driedfruit beetle, Carpophilus hemipterus, and vinegar (fruit) flies, such as Drosophila melanogaster and D. ampelophila, are the primary carriers of sour rot microorganisms and spread these to figs.
Solutions
Pick fruit promptly as it becomes ripe. Promptly remove and dispose of fallen and over-ripe fruit. Selective pruning to improve air circulation within the tree and expose figs dropped beneath trees to heating from the increased sunlight may reduce sour rot.
No bactericides or yeasticides are recommended for controlling sour rot. Promptly remove all types of fruit and any fleshy vegetables from the garden as they ripen or become overripe; this can help reduce the abundance of driedfruit beetle and vinegar flies and this may help to reduce sour rot.
Adapted from Pest Management Guidelines: Fig, University of California Statewide Integrated Pest Management Program (UC IPM). |
A fig fruit with a feeding hole of an adult driedfruit beetle.
Adult driedfruit beetle, a spreader of sour rot bacteria and yeasts.
Adult vinegar fly, a spreader of sour rot bacteria and yeasts.
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