2018 ASHS Annual Conference

The use of beneficial bacteria as a form of biological control in the greenhouse production of floriculture crops is a growing area of interest, but many questions still surround the potential use of bacteria to control plant pathogens. Interest in biological control is increasing because of a desire by both consumers and growers to reduce the use of chemical pesticides. This is particularly important for the control of Botrytis cinerea, which is a fungal plant pathogen that affects many crop species worldwide. This pathogen has become resistant to some fungicides, increasing the urgency to identify alternative control methods. In this study, a collection of 61 Pseudomonas bacteria were screened to identify bacteria that inhibited the growth of Botrytis cinerea. The objective of this study was to develop an in vitro assay that can be used to screen large collections of bacteria and identify those with the potential to control botrytis in floriculture crops. Identifying potential beneficial bacteria from large collections using only greenhouse trials is a difficult task because of the number of plants and greenhouse space required to evaluate large numbers of bacteria treatments. A dual plating assay was developed in which a single Pseudomonas strain was plated on PDA media with the Botrytis cinerea to directly quantify any effects that the bacteria had on the growth of the pathogen. The negative control plates contained botrytis and no bacteria, while cycloheximide was included on the positive control plates in place of the bacteria. When the fungal growth of the negative control plates reached a predetermined point, measurements were taken on all plates to quantify botrytis growth, and determine the zone of inhibition between the bacteria and botrytis. The experiment was designed to provide an initial screen for potential bacteria candidates. Based on the reduction of botrytis growth and the zone of inhibition, approximately twenty of the 61 strains tested were selected as potential biological control agents to use in the reduction of Botrytis cinerea in floriculture crops. This dual plating assay can be used in the future screening of large collections of bacteria, and the selected Botrytis-active pseudomonads will be used in future greenhouse validation trials.