REACTION OF SELECTED TOMATO (Solanum lycopersicum) VARIETIES TOWARDS Meloidogyne incognita AND BACTERIALWILT (Ralstonia solanacearum

Abstract

Tomato (Solanum lycopersicum) is one of the most popular vegetable crops grown worldwide. Tomato cultivation is limited by root-knot nematode (Meloidogyne incognita) and bacterial wilt (Ralstonia solanacearum) diseases. Tomato productivity is also compromised by disease complexes through the interaction of both pathogens. Two greenhouse experiments were designed to evaluate the reaction of tomato varieties to M. incognita and R. solanacearum co-infection and order of inoculation, and to determine the damage threshold inoculum levels of M. incognita and R. solanacearum complex. Four tomato varieties, namely Assila, Chochoro, Marmande and Moneymaker with different levels of disease resistance were evaluated against a single isolate of both M. incognita and R. solanacearum. Six inoculation schedules and inoculum density levels were also considered in this study. The experiments were factorial arranged in a completely randomized design with four replications. Responses of tomato varieties to inoculation schedules and inoculum density levels were made based on disease development parameters, tomato biomass, and growth. Results of the study showed that inoculation schedules significantly (P<0.05) influenced disease and plant parameters. Inoculation of M. incognita 10 days prior to R. solanacearum inoculation led to maximum (3.75) wilt severity at 60 DAI of wilt assessment. Such inoculation schedule reduced plant height, fresh root weight and shoot dry weight by 24.99, 55.96 and 51.88%, respectively. However, sole inoculation of nematode increased all nematode parameters. Severe nematode and bacterial diseases were noted from the variety Marmande. Conversely, variety Assila performed well against the disease compared to other varieties tested. Different inoculum density levels of both pathogens also significantly (P<0.05) affected disease and plant components. An increase in inoculum density levels progressively decreased plant parameters. For instance, at the highest (10,000J2 + 30 ml) inoculum level, fresh shoot weight, shoot dry weight and plant height were reduced by 52.47, 63.12 and 38.99%, respectively. Whereas, bacterial colonization and establishment were highly increased at high inoculum density levels. Also, nematode parameters were more or less optimum at 6000J2 + 20ml to 10, 000J2 + 30ml inoculum levels, implying that 6000J2 + 20ml to 10,000J2 + 30ml inoculum density levels could be considered as damaged threshold levels for both target pathogens. The overall results of this study demonstrated that inoculation schedules and inoculum density levels greatly influenced the response of tomato varieties to M. incognita and R. solanacearum and their complexes. However, studies of such kind should be further executed with many isolates of pathogens, inoculum levels and tomato varieties to verify the validity of the results.