Seed and shoot treatments and the ecology of biological control agents for bacterial and fungal diseases of tomato and pepper
Project code: MU03-PATH03
Diane Cuppels - Agriculture and Agri-Food Canada
To assess biological alternatives to the chemical management of bacterial spot and the fungal diseases anthracnose and early blight in field tomato and pepper
Summary of Results
The objective of this study was to provide efficacy and ecological data and application technologies to support the Canadian introduction of biopesticides commercially-available in the U.S. for control of bacterial spot (Xanthomonas campestris pv. vesicatoria groups A, B, C, D), anthracnose (Colledotrichum coccodes) and early blight (Alternaria solani) on field tomatoes (peppers). All three diseases are now controlled by multiple applications of the heavy metal-based bactericide copper hydroxide and the fungicides chlorothalonil, captan or mancozeb, all of which pose environmental health risks. The biopesticide products that were selected for study were: Streptomyces griseoviridis K61 (Mycostop®), Streptomyces lydicus WYEC108 (Actinovate®), and Pseudomonas fluorescens A506 (BlightBan®). Research was needed on these products as there were no application technologies developed for these diseases, no efficacy data and no Canadian studies regarding their fate/persistence in the environment.
Conclusions: In this study, we (1) used in vitro and in planta assays to confirm the activity of these agents against Ontario isolates of the three pathogens and to determine the best method for applying them to tomato and pepper plants, (2) ran efficacy trials at the London AAFC research farm, and (3) tagged the control agents, as well as the bacterial spot pathogens (all 4 groups of Xanthomonas campestris pv. vesicatoria), with fluorescent protein in order to perform colonization and environmental fate/survival studies.
1) Our in vitro studies indicated that Mycostop® and BlightBan®, but not Actinovate®, strongly inhibit the bacterial spot pathogens, while Actinovate® and Mycostop®, but not BlightBan®, suppress the two fungal pathogens. Scanning electron microscope studies have demonstrated that the streptomycetes are attracted to and degrade or inhibit the hyphae of the fungal pathogens. In planta studies showed that Actinovate®, applied as a spray and Mycostop®, applied as drench, consistently and significantly reduce bacterial spot on greenhouse seedlings with neither adversely affecting the weight and size of the plants. Mycostop® inhibited lesion development by both fungi whether it was applied before or after the pathogen; Actinovate® suppressed lesion formation only when applied as a pretreatment. Yeast extract showed potential as an adjuvant for enhancing the growth of S. griseoviridis in planta.
2) Efficacy trials have shown that both streptomyces have the potential to control bacterial spot of tomato, the amount of control appearing to be dependent on seasonal conditions. Our anthracnose trial, run in 2006, indicated that Actinovate®, Mycostop® and Actinovate®-BlightBan® all can significantly repress lesion development on tomato fruit. With the exception of Actinovate®-BlightBan®, these biopesticide treatments did not have a significant impact on early blight. Perhaps a better application method (timing, adjuvant addition, etc) is needed.
3) The streptomycetes as well as the bacterial spot pathogens were tagged with green fluorescent protein (GFP). These bacteria survived well, after just one initial inoculation, on greenhouse-grown tomato and pepper seedlings over a 14-day period. The GFP label was very stable, being detected after 4-weeks of continuous culture in vitro. Environmental studies of these biocontrol agents would not be possible without GFP-tagging as no growth medium effectively selects out other commonly-occurring streptomycetes in field samples.
Data generated in this project support submission for registration new uses of biocontrol products in Canadian agriculture.
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