New report of Colletotrichum gloeosporioides causing postbloom fruit drop on citrus in Bermuda

Abstract

Postbloom fruit drop (PFD) of citrus was observed for the first time after a widespread and severe outbreak occurred in Bermuda in the 1990s. Fruit losses from the disease were estimated at 25% to 35% in sweet orange, grapefruit, lemon and Tahiti lime. The causal agent of PFD has been reported as either Colletotrichum gloeosporioides or Colletotrichum acutatum. Bermuda isolates of Colletotrichum recovered from diseased orange trees produced lesions typical of PFD in detached petals of orange, lime and grapefruit, and in attached orange blossoms. The isolates produced few to no lesions of anthracnose on leaves of key lime seedlings. Koch's postulates were fulfilled following reisolation of morphologically identical fungi from inoculated tissues. The isolates were characterized using morphological (conidial size and shape and colony colour), physiological (growth rate at 24 °C and on a benomyl-amended medium), immunological (ELISA) and molecular (PCR amplification and sequencing of the ITS region) methods. Immunological and molecular techniques provided definitive identification of the isolates as Colletotrichum gloeosporioides. This report confirms that C. gloeosporioides can be the causal agent of PFD; therefore, identification of the causal agent to species by immunology, molecular analysis and fungicide sensitivity is suggested for new outbreaks of the disease.