Evaluating a diverse panel of biocontrol agents against infection of blueberry flowers by Monilinia vaccinii-corymbosi

Abstract

Seven microorganisms were evaluated for their biocontrol potential against Monilinia vaccinii-corymbosi which causes mummy berry disease through gynoecial (stigma-style-ovary) infection of blueberry flowers: the bacteria Bacillus subtilis QRD137, B. mojavensis RRC101, B. mycoides 7IIC4, and Pantoea agglomerans C9-1S; the yeast Wickerhamiella australiensis Y-27360; and the filamentous fungi Trichoderma harzianum KRL-AG2 and Gliocladium roseum H47. The epiphytic fitness of each organism was investigated by evaluating population dynamics or fungal growth on the stigmas of detached blueberry flowers, and such flowers, co-inoculated with M. vaccinii-corymbosi, were used to determine efficacy in reducing pathogen infection of the style. In addition, all organisms were tested in vitro for antibiosis using dual cultures and for nutrient competition (niche overlap) using Biolog microplates. The most promising antagonists were P. agglomerans, which exhibited high epiphytic fitness on the stigma and consistently reduced stylar infection by the pathogen; B. subtilis, which showed strong antibiotic activity in vitro and considerably reduced pathogen ingress into styles, but whose limited epiphytic fitness decreases its potential for field-use; and G. roseum, which exhibited complete niche overlap with the pathogen in vitro but produced more variable results in reducing stylar infection. Future work should evaluate combinations of these antagonists to determine whether there are additive effects and whether the variability inherent in biocontrol can be reduced.

Keywords:

• blueberry
• mummy berry
• Monilinia vaccinii-corymbosi
• Bacillus subtilis
• Bacillus mycoides
• Bacillus mojavensis
• Pantoea agglomerans
• Wickerhamiella australiensis
• Trichoderma harzianum
• Gliocladium roseum

Acknowledgements

Funded in part by the USDA-CSREES Pest Management Alternatives Program (grant no. 01-34381-11181), the IR-4 Biopesticide Program and the Southern Region Small Fruit Consortium. We thank Charles Bacon, Richard Hanlin and Kenneth B. Johnson for contributing isolates of the organisms used as biological controls. Special thanks to Henry Ngugi for his assistance throughout the project.