An agronomic and microbiological evaluation of various partial sterilants for the greenhouse production of tomatoes in Manitoba

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Portree, James Douglas
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Partial sterilants "Vapam", Diethyl pyrocarbonate (DEPC), methyl bromide, and steam were evaluated for use in greenhouse tomato production. The evaluation consisted of an agronomic examination of yield, quality, maturity, tissue analysis, and a microbiological examination of microflora and microfauna of the cultivars Michigan Ohio and Rapids. Partial sterilants influenced tomato yield, quality, tissue analysis and microbial populations. The treatment steam was associated with the highest marketable yield. The plants in the DEPC-treated plots were associated with the lowest percentage of unmarketable fruit and the highest percentage of number one fruit. Michigan Ohio proved to be the superior cultivar. The elements nitrogen, manganese, and zinc in the tomato tissue samples were affected by the partial sterilants. The steam treatment tissue samples had abnormally high manganese levels. Distinct microflora and microfauna populations were associated with the treatments. Trichoderma spp. and Fusarium spp. were used as 'index organisms' to test treatment influences. Methyl bromide treatment was associated with the higher Trichoderma spp. counts. Penicillium spp. was the dominant microbial group in the steamed plots. The dominance of these groups was directly related to their ability to survive the respective partial sterilants. Mite and nematode populations were affected by partial sterilants. However, they returned to numbers approaching presterilization numbers after one cropping season. Steam was the most effective treatment in terms of increasing yield. Although methyl bromide was marginally different in the characters tested, this marginal difference may be outweighed by its ease of application and effective control of microfauna, microflora groups and weeds.