Hiu-Ling Liao, Huiqin Chen & Kuang-Ren Chung
University of Florida, IFAS Citrus Research and Education Center

Postbloom fruit drop (PFD) of citrus is caused by the fungus Colletotrichum acutatum. The fungus infects flower petals causing brownish lesions that result in young fruit drop, leaf distortion, and formation of persistent calyces (commonly called ‘buttons’) after the fruitlet drops. Previous studies suggested that an imbalance of plant growth regulators such as auxin, ethylene, and jasmonic acid in C. acutatum-infected flowers, may contribute to young fruit drop.

In this study, application of auxin transport and action inhibitors such as 2,3,5-triiodobenzolic acid, clofibrate, or quercetin, jasmonic acid biosynthesis inhibitors such as salicylic acid and aspirin, or gibberellic acid applied 7 days after fungal infection increased retention of young fruit. The commercial products ReZist and Actigard, used as systemic acquired resistance inducers, also increased fruit retention. These products will provide flexibility in treatment timing for reducing postbloom fruit drop in the field since they can be applied after PFD symptoms develop.

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