Influence of propiconazole and metconazole formulations on Bacillus subtilis vegetative cell growth and disease control of fruit crops

Biological control agent (BCA) Bacillus subtilis formulated as Theia® is registered for control of fungal and bacterial diseases of fruit crops. Combinations of Theia® and strategic concentrations of two demethylation inhibitor (DMI) fungicides were investigated to explore potential synergisms. Bacteria were cultured in nutrient broth and combined with technical grades and two formulations of propiconazole (EC and WP) and metconazole (EC and WDG) at 0, 10, 50, 100, and 150 µg/ml active ingredient. After co-cultivation, optical density (OD600) and colony forming units (CFU/ml) were evaluated. In contrast to EC formulations, the WP or WDG formulations at 10 or 50 µg/ml of both DMIs did not affect vegetative cell growth. The mixture of Theia® and each formulated DMI at 50 µg/ml active ingredient resulted in a significant reduction of Monilinia fructicola lesion development on apple, Colletotrichum siamense lesion development on cherry, and Botrytis cinerea lesion development on cherry. The combination of Theia® with EC formulations showed weaker disease reduction due to antagonism. Only Theia® + non-EC formulated propiconazole and metconazole significantly reduced brown rot disease incidence of apple compared to the respective solo treatments and anthracnose disease incidence of cherry compared to the untreated control. Our results indicated that at least some DMI fungicides possess bactericidal effects depending on the formulation and concentration. The combination of Theia® with a lower than label rate concentration (50 µg/ml) of the DMI fungicides propiconazole and metconazole showed potential for synergistic effects especially when non-EC formulations were used.

Impacts of the Ban on the Soil-Applied Fumigant Methyl Bromide

The loss of the soil fumigant methyl bromide (MeBr) and adoption of soil fumigant alternatives has been challenging for farmers, particularly for those crops in which pathogens previously controlled by MeBr have emerged as significant problems, but it has resulted in some unanticipated benefits for the scientific community and the environment. Applauded as one of the most effective environmental agreements to date, the universally accepted Montreal Protocol on Ozone Depleting Substances has had a significant impact on the environment, reducing the release of halogenated compounds from anthropogenic sources enough to mitigate global warming by an estimated 1.1°C by 2021. The funding associated with various MeBr transition programs has increased collaboration across scientific disciplines, commodity groups, industry, and regulatory agencies. Chemical alternatives and improved application strategies, including the development of gas-retentive agricultural films, coupled with sound efficacy data and grower ingenuity have resulted in the sustained production of many of the impacted crops; although there has been some loss of acreage and value, particularly for Florida fumigated crops, but for some, value has continued to increase, allowing production to continue. The loss of a single, broad-spectrum tool for pest control has led to a deeper understanding of the specific pest complexes impacting these at-risk crops, as well as the development of new, biologically based management tools for their control, while increasing our understanding of the role of the soil microbiome in pest control and crop production.

Elucidating the Mode of Action of Hybrid Nanoparticles of Cu/Zn against Copper Tolerant Xanthomonas euvesicatoria

The widespread presence of tolerance to copper in Xanthomonas species has resulted in the need to develop alternative approaches to control plant diseases caused by xanthomonads. In recent years, nanotechnological approaches have resulted in the identification of novel materials to control plant pathogens. While many metal-based nanomaterials have shown promise for disease control, an important question relates to the mode of action of these new materials. In this study we used several approaches such as SEM, propidium monoazide qPCR, epifluorescence microscopy and RNA sequencing to elucidate the mode of action of a Cu/Zn hybrid nanoparticle against copper tolerant strains of Xanthomonas euvesicatoria. We demonstrate that Cu/Zn, unlike Kocide 3000, did not activate copper resistance genes (i.e. copA and copB) in the copper-tolerant bacterium, but functioned by disrupting the bacterial cell structure and perturbing important biological processes such as cell respiration and chemical homeostasis.