Ethylene, Fungi, and Summer Fruit Drop of Navel Orange1

Abstract

Species of Alternaria and Gloeosporium were most often isolated from fruit with blossom-end yellowing (BEY), a disorder associated with summer fruit drop of navel orange [Citrus sinensis (L.) Osbeck]. Fruit inoculated with pure cultures of these fungi did not develop BEY; however, wounded fruit which were inoculated with fungi produced higher levels of ethylene and more extensive BEY than wounded, noninoculated fruit. Fruit with BEY produced higher amounts of ethylene than symptomless fruit. The methoxy analog of rhizobitoxine (methoxyvinylglycine) did not reduce ethylene levels, and silver nitrate increased ethylene production from fruit with BEY. Ethylene and fungi are associated with BEY of navel orange but do not appear to be causal factors.