Colletotrichum acutatum causes post-bloom fruit drop and lime anthracnose on citrus
In the new edition of the APS Compendium of citrus diseases, it is explained that there are three anthracnose diseases of citrus caused by Colletotrichum species. Colletotrichum acutatum (EU Annexes) is the causal agent of two diseases: post-bloom fruit drop and lime anthracnose. Colletotrichum gloeosporioides causes a post-harvest anthracnose which usually appears on bruised or injured fruits.
Post-bloom fruit drop is widespread throughout humid, and subtropical regions of the Americas. It can cause serious crop losses during in high rainfall areas and sporadic outbreaks elsewhere. C. acutatum infects flower petals and induces drop of fruitlets. The fruitlet usually abscises at the base of the ovary, and the floral disk, calyx and peduncle remain attached to the tree. Leaves surrounding an affected inflorescence are usually small, chlorotic, twisted and have enlarged veins.
Lime anthracnose was originally thought to be caused by Gloeosporium limetticola (a name of uncertain status which was previously listed in the EU Annexes), but its causal agent is C. acutatum. The lime anthracnose strain only affects Mexican lime (Citrus aurantifolia) and it occurs throughout the humid areas of the Americas, in Zanzibar and is probably present in other humid citrus-growing areas. It affects flowers, young leaves shoots and fruits. Infected fruitlets also drop. Another difference with post-bloom fruit drop, is that the pathogen produces acervuli on all tissues (leaves, twigs, flowers and fruit) whereas the post bloom fruit drop pathogen produces acervuli only on flower petals.
The EPPO Secretariat had previously no data on citrus being a host of C. acutatum.
Sources
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Timmer, L.W. (2000) Anthracnose diseases. In: Compendium of Citrus Diseases, 2nd edition (Ed. by ;L.W. Timmer, S.M. Garnsey, J.H. Graham), APS, USA. p 21-23.
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