Effectiveness Of Trichoderma Spp., Bacillus Spp. And Pseudomonas Fluorescens In The Management Of Early Blight Of Tomatoes

Abstract

Tomato, a major vegetable widely used in Kenya faces a number of production challenges some of them being diseases like late blight, early blight and bacterial wilt. Chemical compounds which have environmental and health concerns are mostly used to control early blight in tomato production. In this study, two Trichoderma isolates, two Bacillus isolates and commercial Pseudomonas fluorescens were used in the management of early blight, a major disease of tomato. These were tested for their effectiveness in managing Alternaria solani in vitro. The dual culture technique was used and consisted in growing the antagonists together with the pathogen. Diameter of A. solani colony was measured and used to calculate the percent growth inhibition. Trichoderma isolates were the most effective against the radial growth of A. solani with percent growth inhibition of 80.9 and 82.2%. These were followed by Bacillus isolates with percent growth inhibition of 56.6 and 54.1%. Pseudomonas fluorescens also suppressed A. solani radial growth but with a lower percent growth inhibition of 47.6%. Trichoderma isolates, Bacillus isolates and commercial Pseudomonas fluorescens were also evaluated for their effectiveness in managing tomato early blight under greenhouse and field conditions. Water and Tower 72 WP® (Metalaxyl 8% and Mancozeb 64%) were used as control and standard check respectively. Data were collected on disease parameters and yield of marketable fruits. In the greenhouse, 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 from Tricho 7, followed by the standard chemical with a comparable yield of 0.20 kg/plant. Control treatment recorded xvii significantly lower marketable fruit weight of 0.06 Kg/plant. At both experimental sites, on the 90th day 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 antagonists was from 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. Trichoderma spp., Bacillus spp. and Pseudomonas fluorescens are effective in managing early blight under in vitro, greenhouse and field conditions and they are able to reduce the effects of early blight on tomato production. They should be used for a sustainable production of tomatoes. Key words: Trichoderma spp., Bacillus spp., Pseudomonas fluorescens, management and early blight of tomatoes.