Publications - Faculty - Recently Submitted Faculty Publications 2008

Timmer - Plant Disease

Non-Postbloom Fruit Drop Strains of Colletotrichum acutatum Can Colonize Citrus Leaves and Produce Conidia in Response to Citrus Flower Extracts

S.J. MacKenzie, N.A. Peres and L.W. Timmer

ABSTRACT

A single strain of Colletotrichum acutatum causes epidemics of postbloom fruit drop (PFD) of citrus throughout the Americas.  This strain infects flowers, where it produces necrotic lesions on petals and the abscission of fruitlets.  It survives on vegetative tissues during non-flowering periods and conidiation on colonized tissue is stimulated by flower extracts.  Genetically distinct strains from other hosts can cause PFD symptoms, but it is not clear if they can survive on vegetative tissue and sporulate in response to flower extracts.  In the present study, isolates from anthracnose-affected blueberry, leatherleaf fern, strawberry, and Key lime and PFD-affected sweet orange were evaluated for their ability to survive surface disinfection of tangelo leaves up to 27 days after inoculation and to produce conidia in response to flower extracts.  Viable propagules were recovered from tissue inoculated with all non-PFD isolates after surface disinfection and some non-PFD isolates were recovered at incidences equal to or greater than those of the PFD isolate.  Colonies recovered from leaf washes increased for all isolates after flower extract treatment.  The number of propagules recovered was comparable across isolates and there was no evidence that the multiplicative increase differed among isolates.  Application of 2.5% sucrose to leaves inoculated with the PFD isolate also increased the number of colonies recovered from washes, suggesting that the increased growth and conidiation observed after flower extract treatment are nutritional responses.