Management of Bacterial Spot of Pepper Caused by <i>Xanthomonas campestris</i> pv. vesicatoria

Abstract

Isolation trials from pepper leaves showing bacterial spot collected from Giza, Kalubia and Behera governorates yielded 13,12,9,6 isolates of Bacillus subtilis, Pseudomonas spp., Xanthomonas campestris pv. vesicatoria and P. fluorescens, respectively. The isolated strains of X.c. pv. vesicatoria were yellow Gram negative of short rods and produced Xanthomonadins and the other identification criteria proved that these isolates are X.c. pv. vesicatoria. Pathogenicity test of these isolates on Balady pepper cv. indicated that all of them were pathogenic and isolate No.3 of Kalubia governorate resulted in the highest infection. P. putida was most efficient bioagent in inhibiting of the pathogenic bacterium followed by P. fluorescens, while B. subtilis was the lowest efficient one. The fungicide Efdal Bakirox was the most efficient one in inhibiting growth of the causal bacterium on the medium more than the fungicides Roxil and Tango. The fungicide Tango and Roxil failed to cause any inhibition to the causal bacterium at 100 ppm. Field experiments during 2014 and 2015 growing seasons revealed that spraying pepper plants with the tested bioagents and the fungicides four times resulted in significant reduction to the severity of the natural infection by the causal bacteriaum with significant increase to the produced fruit pods compared with the control. The tested fungicides were more efficient in this regard than the bioagents. Roxil was the most efficient treatment in reducing the severity of the disease and increasing the produced pod yield. Meanwhile, the bioagent B. subtilis was the lowest efficient treatment and the other treatments recorded intermediate figures. Total phenols and vitamin-c content as well as the activity of chitinase, peroxidase and polyphenoloxidase in pepper leaves infected by X.c. pv. vesicatoria were greatly lowered in the infected leaves compared with the uninfected leaves and the tested bioagents and fungicides resulted in considerable increase to these chemicals compared with the infected leaves.