MANAGEMENT OF TOMATO (Solanum lycopersicum L.) LATE BLIGHT [Phytophthora infestans (Mont.) de Bary] THROUGH HOST PLANT RESISTANCE AND FUNGICIDE APPLICATION IN GAMO GOFA ZONE, SOUTHERN ETHIOPIA

Abstract

Tomato is one of the most important vegetable crop in Ethiopia. Diseases are major constraints that limit production of tomato in the country. Late blight is a very severe disease in most tomato-growing regions, including the Gamo Gofa Zone, where information on disease management options through integration of varieties and fungicide applications are inadequate. A field experiment was conducted at Arbaminch Agricultural Research Center during 2016 main cropping season with three objectives to: 1) evaluate the effect of varieties by fungicide application frequencies on late blight (Phytophthora infestans) epidemics; 2) determine the effects of host plant resistance and fungicide on fruit yield and yield components of tomato; and 3) determine the economics of fungicide spray for the management of tomato late blight. The treatments consisted of four tomato varieties (ARPTD2, Bishola, Roma VF and Melkasholla) and five foliar spray frequencies, including unsprayed plots as a control and were laid out in a factorial arrangement in a randomized complete block design with three replications. To achieve the objectives of the study important parameters were collected; incidence and severity of late blight, and growth and yield related traits of tomato. Integration of varieties and fungicide spray frequencies significantly reduced late blight epidemics and increased fruit yield. Disease severities, as low as 25.92, 31.78, 38.71 and 44.51% were recorded on ARPTD2, Bishola, Roma VF and Melkasholla varieties, respectively, when ridomil was sprayed four times at 10 days interval. The highest AUDPC values of 826.43, 1011.12, 1134.25 and 1245.52% days were recorded from unsprayed plots of ARPTd2, Roma VF, Bisholla and Melkasholla varieties, respectively. Similarly, the lowest late blight progress rates of 0.0352, 0.0379, 0.0421 and 0.0431 units per day were also recorded on ARPTD2, Roma VF, Melkasholla and Bisholla varieties, respectively, as a result of four times sprays with ridomil at 10 days interval. Late blight severity, AUDPC and disease progress rate were reduced in variety ARPTD2 as compared to the other three varieties. Three times foliar applications with ridomil at 10 days interval xix proved to be an effective treatment against tomato late blight and gave the highest (44.16 t ha-1) marketable fruit yield over the control (22.92 t ha-). Fruit yield loss of up to 42.53 % was calculated on unsprayed control plots as compared to highly treated or protected plots. Marginal analysis indicated that the highest 40.00% and 41.30% marginal rate of return in comparison with unsprayed plots was obtained where ridomil at two times for ARPTD2 variety and three times for Roma VF spray variety spray frequencies was used, respectively. In conclusion, integrations of varieties and two times for ARPTD2 and three times for Roma VF, Bisholla and Melkasholla varieties ridomil foliar sprays at 10 days interval were found to be an effective treatment in reducing tomato late blight epidemics and increasing fruit yield. Thus it is recommended to use this spray frequency as it gave the highest protection against late blight and the highest monetary benefit as compared to the other treatments and the control. However, further extensive studies have to be undertaken for developing concrete recommendation for late blight management options through integration of varieties and fungicide applications that may contribute to sustainability by stabilizing tomato production in the country.