Effectiveness of Bio-control Agents in the Management of Early Blight of Tomatoes

Abstract

Tomato, a major vegetable widely used in Kenya faces a number of production challenges along with diseases like late blight, early blight and bacterial wilt. In this study, bio-control agents (BCAs) which are deemed to be environmentally friendly were used for the management of early blight, a major disease of tomato. BCAs including two Trichoderma isolates coded Tricho 7 and Tricho 10, two Bacillus subtilis isolates coded CA51 and CB12 and Pseudomonas fluorescens (from commercial Bio-cure) were tested for their effectiveness in managing Alternaria solani in vitro. The experiments were carried out in Plant Pathology Laboratory at the Department of Plant Science and Crop Protection, University of Nairobi. The dual culture technique was used. The experimental design was a Completely Randomized Design in five replicates. Diameter of A. solani colony was measured and used to calculate the percent growth inhibition. Means were compared using Fisher’s protected least significant difference (LSD) test at 5%. Tricho 7 and Tricho 10 were the most effective against the radial growth of A. solani with percent growth inhibition of 80.9 and 82.2% for Tricho 7 and Tricho 10 respectively. These were followed by CA51 and CB12 with percent growth inhibition of 56.6 and 54.1% respectively. Pseudomonas fluorescens also hindered A. solani radial growth but with a lower percent growth inhibition of 47.6%. The same BCAs were evaluated for their effectiveness in managing tomato early blight under greenhouse and field conditions. Water and Tower (Metalaxyl 8% and Mancozeb 64%) were used as control and standard check respectively. Greenhouse evaluations were carried out at Kabete Field Station. The experimental design was a Completely Randomized Design in four replicates. Data were collected on disease and plant parameters. The percent disease index by the 90th day after transplanting was significantly lower in all treatments than in the control. Isolate CB12 recorded the lowest percent disease index of 28.3% which was comparable to the standard

chemical at 30.5% and both were significantly different from the control at 61.6%. The highest mean quantity of marketable fruits of 0.21 kg/plant was recorded with Tricho 7, followed by the standard chemical with a comparable yield of 0.20 kg/plant. Control treatment recorded significantly lower marketable fruit weight of 0.06 Kg/plant. Field evaluations were carried out at Kabete Field Station and at Kenya Agricultural and Livestock Research Organization (KALRO) Mwea. A Randomized Complete Block Design in triplicate was used. At both experimental sites, on the 90th days after transplanting, the percent disease index was significantly lower in all the treatments compared to the control. The lowest percent disease index recorded for the BCAs was with Tricho 10 at 35.0% and was comparable to the standard chemical at 30.3%. The two were significantly lower than the control at 68.8%. As for yield of marketable fruits, Tricho 10 recorded significantly higher mean weight at 10.5 tons/hectare compared to the control which recorded 3.8 tons/hectare. However, the standard chemical recorded significantly higher yield at 11.7 tons/hectare compared to Tricho 10. BCAs are effective in managing early blight in vitro and under greenhouse and field conditions and minimize the effects of early blight on tomato production. Key words: bio-control agents, management, tomato and tomato early blight.