Relation of Nutrition of Tomato to Disposition to Infectivity and Virulence of Fusarium lycopersici

Abstract

1. Experiments were conducted to study the relation of nutrition of the tomato as a factor in its disposition to the infectivity and virulence of Fusarium lycopersici. Bonnie Best (susceptible) and Marglobe (resistant) varieties were tested. Nutrition was varied by the application or non-application of nitrates under otherwise identical conditions. The substrate was inoculated both previous (pre-inoculation) to and subsequent (post-inoculation) to the establishment of the plants. 2. Recovery of the fungus from the base of the stem was used as a criterion of infectivity and infection. Manifestation of macroscopically detectable symptoms was used as a criterion of virulence and of pathic effects in the host. 3. Results of the nutritional experiments revealed (a) a high frequency of infection of both resistant and susceptible tomato plants under minus nitrate nutrition; (b) a low frequency of symptoms in plants under minus nitrate nutrition; (c) no wilting in the so-called resistant Marglobe under either type of nutrition; (d) seedlings of the resistant variety under either plus or minus nitrate culture readily infected and producing symptoms identical with those of the susceptible variety. 4. Type of inoculation and age of the plant are important factors in infection and symptom production: (a) Pre-inoculation of sand led to a higher frequency of infection and symptom production. (b) Post-inoculation of sand under minus nitrate culture did not lead to the development of any plant symptoms, even in infected plants. (c) Bonnie Best variety under plus nitrate nutrition showed a high frequency of infection and of symptom production of both the chronic and the acute type, at all seasons of the year, when either pre-inoculation or post-inoculation was used. (d) Pre-inoculation practically halved the incubation period. 5. Browning of vascular bundles of the stem alone is an inadequate criterion of infection. Even under minus nitrate nutrition, 35.4 per cent of the infected plants did not manifest brown bundles at the base of the stem.