EVALUATION OF TOMATO VARIETIES FOR RESISTANCE TO TOMATO LEAFMINER (TUTA ABSOLUTA) IN KIRINYAGA COUNTY, KENYA

Abstract

The tomato leafminer (Tuta absoluta) (Meyrick) (Lepidoptera: Gelechiidae) is an invasive insect pest of tomato crops in many parts of Africa. It causes substantial economic losses to tomato crops in Kenya. Majority of farmers have resulted to intensive insecticide application that has led to development of insecticide resistance. It is therefore critical to develop sustainable management strategies that can be used in Integrated Pest Management (IPM) programmes against the tomato leaf miner. Genetic breeding against the tomato leaf miner can be promising since effective cultural control is difficult. The objective of this study was to evaluate level of resistance of popular tomato varieties to tomato leaf miner in Kirinyaga County, Kenya. The four tomato varieties Rambo F1, Pesa F1, RiograndeVF and Cal J were evaluated for resistance against T. absoluta under field conditions. Mwea East Sub-County is characterised by intensive tomato production, diverse cultural practises and high usage of synthetic pesticides against the tomato leaf miner. The experiment was laid out in a randomized complete block design in two locations (Kariithi and Kimbimbi), which have irrigation schemes that allows tomato production throughout the year. Presence of mines was assessed on leaves obtained from the lower, intermediate and upper canopy of tomato plants at days 20, 40, 60 and 80 after planting. Fruit damage was estimated at the end of the cropping cycle. Data was subjected to arcsin square root transformation and analysis of the level of pest damage on different tomato varieties, was done using general linear mixed effects models, performed using the lme function in the nlme package in R 3.4.2.The results of this study show that larvae mining damage on the leaves was observed in all the evaluated tomato varieties, but it was significantly higher on Pesa F1 hybrid variety (p > 0.001) than Riogrande VF and Cal J. Fruit damage was also significantly higher on Pesa F1 variety (p > 0.01) than Riogrande VF and Cal J. These results suggest that most of the commercially grown tomato varieties are susceptible to T.absoluta infestation. However, Riogrande VF and Cal J can be incorporated in IPM programs. Further studies need to be done for introgression of resistance genes from wild varieties into cultivated tomato varieties.