An in vitro method for screening Colletotrichum gloeosporioides as a biological control agent for western hemlock dwarf mistletoe

Abstract

An in vitro system using detached western hemlock branches infected with dwarf mistletoe was developed to screen the virulence of five isolates of Colletotrichum gloeosporioides, a hyperparasite of dwarf mistletoe shoots and berries. Detached branches infected with dwarf mistletoe were placed in nutrient-saturated rock-wool blocks and mistletoe shoots were inoculated with a conidial suspension of C. gloeosporioides. One month after inoculation, lesions on mistletoe stems and berries were well developed. Infection levels for individual isolates varied from 40% to 60% of shoots and 60% to 80% of berries. Significant differences were found between the isolates and control (p = 0.02 and 0.001, respectively) while no differences were noted between the isolates for both the shoots and berries. Parallel inoculation of mistletoe shoots detached from hemlock branches on moist filter paper and in rock-wool blocks failed because these shoots deteriorated rapidly, fragmenting into segments within a week. This in vitro test may provide an alternative method for rapid screening of potentially virulent C. gloeosporioides isolates. © 2009 Crown in the right of Canada.