Studies on the Wilt disease complex in Tomato (Solanum lycopersicum L.) and it’s management
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Date
2015
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Abstract
In recent years India is emerging as an important producer of vegetables and fruit crops. Among
the vegetables, tomato is gradually gaining importance as it is switching from a seasonal to year-round
cultivable crop. At the same time it is affected by several diseases among which wilt disease is the most
important one causing severe reduction in fruit yield.
The severely wilted tomato plants were collected from the infested fields of Orissa University of
Agriculture and Technology (OUAT) research plots and associated pathogens i.e both fungus and
bacterium were isolated and identified as Fusarium oxysporum f. sp. lycopersici and Ralstonia
solanacearum respectively on the basis of cultural and morphological characters and final confirmation
was done by testing the pathogenicity. The tomato plants were inoculated singly with either of the
pathogen and also combinedly. It was observed that mortality (Pre and post emergence) was highest in
combined soil and seed application of F. oxysporum f. sp. lycopersici and R.solanacearum.
In culture the fungus produced three types of asexual spores i.e. macroconidia, microconidia and
chlamydospore. The macroconidia were slightly curved or sickle shaped and four to five celled.
Microconidia were smaller and one celled. Chlamydospores were roundish and were formed on or in
mycelium. Isolated bacterium was Gram negative , short rod with rounded ends. Average cell length was
found to be 0.78µm. Biochemical characterization of R. solanacearum showed positive results for Citrate
tests and negative results were revealed from Indole, Methyl red and Voges Prosker test.
Cultural studies revealed that Tochinial’s agar media or broth and King’s B media are most
suitable for the growth of the fungal and bacterial pathogen respectively. Sorbitol (C6H14O6) and Sodium
Nitrite (NaNO2) were found to be the best source of Carbon and Nitrogen for the test fungus with
production of 353.3mg and 326.6mg mean dry mycelia mat respectively. The test fungus grew well at
neutral to slightly acidic broth and it was favoured by exposure to 8 hours light and 16 hours darkness.
Soaking of tomato seeds in culture filtrate of the test fungus resulted in increased germination percentage.
From management study, it was revealed that among the phytoextracts tested, Eucalyptus leaf
extract resulted in the highest inhibition (73.71%) of mycelia growth of the test fungus at 20%
concentration. Among the tested essential oils, clove oil gave 99 - 100% control of the test fungus
F. oxysporum f. sp. lycopersici at 1% concentration. Among the tested bioagents Trichoderma viride and
Pseudomonas fluorescens were found to be the most effective in controlling F. oxysporum
f. sp. lycopersici and R. solanacearum . In vitro evaluation of fungicides revealed that highest percent
growth inhibition (91.01%) was obtained in case of Carbendazim 50% WP against F. oxysporum
f. sp. lycopersici.