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Shoot and Flower Blight of Leucospermum cordifolium Incited by a Benomyl-Tolerant Strain of Botrytis cinerea. J. J. Cho, Research Associate, Department of Plant Pathology, University of Hawaii, Maui Agricultural Research Center, Kula, Maui, HI 96790; Phytopathology 67:124-127. Accepted for publication 7 June 1976. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-124.

Botrytis cinerea consistently was isolated from blighted shoots and flowers of Leucospermum cordifolium in Kula, Hawaii. Several benomyl-tolerant isolates were isolated at the Maui Agricultural Research Center, Kula, after continuous applications of benomyl. However, benomyl-tolerant isolates were not present in an adjacent field where benomyl had not been applied. A B. cinerea isolate (B1) tolerated high concentrations of benomyl in spore germination and mycelial growth tests. At the highest concentration of benomyl (500 μg/ml) spore germination of B1 was 98.6%, whereas a benomyl-sensitive isolate (B4) showed 8.9% germination. Mycelial growth of B1 was inhibited slightly (81.6% and 60.3%) by benomyl at 250 μg/ml and 500 μg/ml. In contrast, two benomyl-sensitive isolates (B3 and B4) were inhibited completely at the lowest benomyl concentration tested (1.0 μg/ml). Isolate B1 also exhibited tolerance to methyl-thiophanate and thiabendazole at 250 μg/ml and 500 μg/ml, respectively, whereas the benomyl-sensitive isolates (B3 and B4) did not. Captan was the least effective in inhibiting the growth of any isolate. At a high concentration (500 μg/ml) mancozeb reduced the growth of all isolates. On the other hand, chlorothalonil required low concentrations (10 μg/ml and 25 μg/ml) to inhibit the growth of all isolates. Both the benomyl-tolerant isolate (B1) and the benomyl-sensitive isolate (B3) induced blight of flowers and young shoots of container-grown L. cordifolium plants and produced symptoms similar to those observed in the field.

Additional keywords: ornamental protea, Banksia speciosa, benzimidazole fungicides.