Improved efficacy of formulated bacteriophage in control of black rot caused by Xanthomonas campestris pv. campestris on cabbage seedlings

The survival of bacteriophage in the phyllosphere is influenced by many factors, including sunlight UV irradiation. The effect of the UV light factor on persistence of the phage mixed with different UV-protectors was evaluated in vitro and in planta on young cabbage plants in greenhouse. The exposition of UV irradiation positively correlated with phage population decline. The protective formulations reduced the UV effect. In in vitro studies, ascorbic acid, riboflavin and skimmed milk caused significant phage protection if applied together with phage application. UV light was responsible for detrimental effects on phages placed on plant foliage in the glasshouse experiments. In order to demonstrate direct effects of UV-protectants, phage suspensions with different compounds were exposed to UV irradiation and assayed for effectiveness against black rot disease of brassicas caused by Xanthomonas campestris pv. campestris. The protective formulation eliminated the effects of UV irradiation and probably other environmental factors.