Assessing the Potential for Colletotrichum Acutatumas a Biological Thinning Agent for Florida Citrus

Abstract

Colletotrichum acutatum,causal agent of postbloom fruit drop of citrus, and two induced C. acutatummutants (3-3 and 3-2) were tested as potential agents for reducing fruit load on ‘Valencia’ sweet or ange ( Citrus sinensis) and ‘Temple’ tangor ( C. reticulata x C. sinensis). Wild-type C. acutatumRST and a C. gloesporioidesisolate were applied as conidial suspensions while induced mutants of C. acutatum(3-3 and 3-2), which produced few conidia in culture, and the wild-type isolate RST resulted in the characteristic blossom infection and persistent enlarged calyxes (“buttons”) associated with postbloom fruit drop. The bloom period in 1999 was extremely dry and only the mycelial suspensions of RST resulted in significant formation of PFD buttons. In 2000, some rain occurred during bloom, and conidialsus pensions of RST resulted in greater button formation than did the mycelial suspensions. No other treat ments resulted in greater button formation than was observed in non-inoculated controls, and little natural PFD was observed. At harvest, there were no differences in fruit load or fruit size among trees inoculated with wild-type C. acutatum,mutant C. acutatumisolates, the C. gloeosporioidesisolate and non-inoculated controls.