Efficacy of Five Selected Bacterial Antagonists in Suppressing Foliar Colonization of Colletotrichum truncation on Capsicum annuum

Abstract

Capsicum annum (chilli) leaves serve as a major source of inoculum for the anthracnose causing fungus Colletotrichum truncatum. For successful infection, pre-penetration events including strong adherence to the host surface and spore germination play a critical role. As a novel approach, possible suppression of C. truncatum leaf infection by antagonistic bacteria was investigated in this study. Abaxial surface of surface sterilized healthy, freshly detached chilli leaves were spot inoculated with 30 pi of C. truncatum spore suspension (106 spores/ml) followed by 30 pi of cell suspension (108 cells/ml) of each F2, F35, F65, F79 and F80 each antagonists separately. The treated leaves were incubated in a humid chamber under dark conditions. One square centimeter of leaf tissues was excised at different time points, viz. 6 Hours after inoculation (HAI), 12 HAI, 36 HA1, 48 HA1, 60 HA1 and 72 HAL Excised leaf tissues were then transferred to a clearing solution (absolute alcohol: acetic acid, 1:2). Tissues were cleared for 24 hours in the clearing solution and then washed with sterilized distilled water. Carefully blot dried tissues were mounted on microscopic slides in lactophenol cotton blue stain. Germinated spore counts and appressorial counts were taken from the tissues excised at different incubation periods. Light microscopic views of untreated control demonstrated the sequence of colonization of C. truncatum3t the tested time points. In contrast, F2, F65, F79 and F80 treatments completely inhibited the spore germination and subsequent colonization, possibly through hampered spore attachment. However, F35 antagonist significantly reduced the spore germination and limited the colonization process only up to appressoria formation. The results of this study suggest the possibility of using these antagonists in foliar applications in preventing chilli leaf colonization of C. truncatum.