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Thigmomorphogenesis and Predisposition of Hosts to Fusarium Wilt. Omar Shawish, Graduate student, Department of Botany and Plant Pathology, Colorado State University, Fort Collins 80523; Ralph Baker, professor, Department of Botany and Plant Pathology, Colorado State University, Fort Collins 80523. Phytopathology 72:63-68. Accepted for publication 24 April 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-63.

Tomato, flax, and pea plants were subjected to mechanical stimulation (MS) in a greenhouse environment by gently shaking the stems and leaves for 1 min each day. The incubation period for development of Fusarium wilt, which is induced by various formae speciales of Fusarium oxysporum, was shorter than in inoculated plants not exposed to MS. Symptom expression also was more severe in MS-treated plants as measured by foliar symptoms and vascular discoloration. This increase in symptom expression was accompanied by reduction in stem length and increase in stem thickness as a result of MS in comparison with untreated controls. Cuttings were taken from tomato plants and inoculated with F. oxysporum f. sp. lycopersici. These were rooted for 15 days and transplanted. Half of the transplants were subjected to MS and half were not. All combinations of MS-treated, untreated, and inoculated and uninoculated controls also were included in the experiment. Symptom expression, as measured in foliar responses, was significantly (P = 0.05) most severe in plants treated with MS both on the mother plants and as transplants followed in descending order by those treated only as transplants, only as cuttings on the mother plant, and untreated inoculated controls. Similar responses were observed when transplants were derived from seedlings rather than cuttings from mother plants in the same experimental design. These phenomena suggest that there was a long-term effect of MS on disease expression after MS was withdrawn because transplants treated while they were on mother plants or as seedlings had more severe foliar symptoms than untreated controls. In the field, MS is furnished predominantly by wind. Thus, wind may be added to the list of predisposing factors in epidemiology which have an effect on disease expression.

Additional keywords: resistance.