The causal agent of citrus postbloom fruit drop, Colletotrichum acutatum, can survive on weeds

Postbloom fruit drop is an important citrus disease caused by Colletotrichum acutatum. Severe outbreaks can develop when rainy periods occur during citrus bloom. Under these conditions, explosive epidemics are observed despite relatively short inoculum dispersal distances typical of this pathogen. C. acutatum can survive on citrus leaf surfaces after formation of appressoria, but survival on weeds has not been characterized. The survival of C. acutatum on seven species of weeds was evaluated under greenhouse conditions by artificial inoculation and subsequent recovery of the pathogen in-vitro. Conidial germination and appressorial development of C. acutatum were observed on the surface of all inoculated leaves. The pathogen was recovered from weed leaves at 30, 60 and 90 days after inoculation. Statistically, there was no difference in survival of C. acutatum among sample times post-inoculation. Although survival varied on different weed species, no symptoms were observed on inoculated leaves. All citrus flowers inoculated with isolates recovered from inoculated weeds showed typical symptoms of postbloom fruit drop. We conclude that the weed species tested may serve as potential alternative hosts for C. acutatum.