Applications of Bacillus subtilis and Trichoderma spp. for controlling the potato brown rot in field

Abstract

Possibilities of biological control of brown rot disease caused by Ralstonia solanacearum were investigated in a greenhouse and in a naturally infested commercial potato field. Three biocontrol agents (BCAs) namely Bacillus subtilis, Trichoderma album and Trichoderma hamatum, isolated from commercial potato field and identified in the Department of Plant Pathology, National Research Centre in Egypt. In the greenhouse experiment, B. subtilis as seed tuber treatment significantly reduced the bacterial wilt disease incidence in potato cvs. Diamante and Spounta, followed by T. hamatum and T. album compared with the controls. Three field experiments were carried out as follows: (i) the first experiment during the winter of 2006/2007 seasons, (ii) the second during the summer of the 2007 season, and (iii) the third during the winter of 2007/2008 seasons. The BCA treatments improved the vegetative growth parameters such as plant height, stem number/pit and leaf number/plant compared with the control plants. The treatments also enhanced the average tuber weight and tuber yield/plant. Field application of the BCAs as tuber and/or soil treatments significantly reduced the brown rot incidence and bacterial wilt severity. In the first experiment, the BCA treatments reduced the brown rot incidence in potato cv. Diamante from 15.3 to 21.3% compared with 21.9% in the untreated plants. In the second experiment, the percentage of bacterial wilt severity (BWS) in treated potato cv. Nicola was in the range 18.0–22.0% 60 days after planting compared with 38.0% in the control plants. The percentage disease control was in the range 42.1–52.6%. The brown rot incidence (BRI) was in the range 21.2–46.3% as tuber treatment and 18.9–29.1% as soil treatment in treated potato plants compared with a disease incidence of 60% in the control plants. In the third experiment, the BWS was less than 8% in treated potato cv. Diamante, compared with 16% in control plants 60 days after planting. T. hamatum completely protected the potato tubers against brown rot, than T. album and B. subtilis as well as the control. The BCA as soil treatments were more effective than tuber treatments for decreasing the BRI in potato and enhancing the growth and tuber yield parameters. This study revealed that B. subtilis, T. hamatum and T. album are promising as BCAs which are effective under field conditions for controlling potato brown rot.