Evaluation of Biological Control Agents and Conventional Products for Post-Harvest Application on Potato (Solanum tuberosum L.) to Manage Leak

Biological control agents applied post-harvest may provide an effective way to manage leak of potatoes by competing with Pythium ultimum . The objective of this paper was to test the efficacy of various biological control agents and conventional post-harvest fungicides to manage leak. Two studies were performed with a Pseudomonas fluorescens triculture including desiccation tolerant variants of strains S11P12, P22Y05, and S22T04 in three formulations (a “fresh” triculture, dried on Kenite 700, or dried on Attapulgite clay) applied at a rate of 3.5 mL kg −1 . A third study contained treatments of the P. fluorescens “fresh” triculture, triculture dried on Kenite, triculture dried on Kenite blended with a fungicide containing a three-way mixture of azoxystrobin, fludioxonil, and difenoconazole (Azo+Flu+Dfz, 0.033 mL kg −1 ), and triculture dried on Kenite rehydrated with nutrient broth Medium 1 blended with the same fungicide. Other treatments included Pseudomonas syringae (3.5 mL kg −1 ) in Studies 1 and 2, while hydrogen peroxide and peroxyacetic acid (0.042 mL kg −1 ), phosphorous acid (4.2 mL kg −1 ), and Azo+Flu+Dfz (0.033 mL kg −1 ) were used in all three studies. The three studies were each repeated twice using unwashed tubers (cv. ‘Russet Burbank’) that were wounded and inoculated with P. ultimum . After inoculation, tubers were treated, then stored at 21 C for four days prior to disease evaluation. In Study 1, none of the formulations of P. fluorescens triculture significantly controlled leak compared to the inoculated control; however, the “fresh” triculture formulation significantly decreased leak incidence by 24% in Study 2. In all three studies the three-way fungicide mixture Azo+Flu+Dfz resulted in lower leak incidence (1, 7, and 24%, in studies 1, 2, and 3 respectively) compared with the inoculated control (12, 37, and 50% leak incidence, in studies 1, 2, and 3 respectively). Study 3 showed the formulations of P. fluorescens strains were not effective in leak control but when combined with Azo+Flu+Dfz leak incidence significantly decreased compared to the inoculated control. The lowest leak incidence was seen when the triculture component of the fungicide mix was rehydrated with Medium 1 in Study 3. The P. fluorescens triculture formulations mixed with Azo+Flu+Dfz and rehydrated with Medium 1 had slightly higher bacterial counts than the “fresh” triculture and the triculture dried on Kenite, potentially indicating a greater activity level affor