A Physiological Study of the Fusaria Causing Tomato, Cabbage and Muskmelon Wilts

SUMMARY

A physiological study has been made of three Fusarium formae in the section Elegans: F. oxysporum f. lycopersici, F. oxysporum f. conglutinans and F. oxysporum f. niveum, with the purpose of determining differential reactions. It was observed that all the isolates utilized arabinose, xylose, glucose, maltose, dextrin, glycerol, mannitol, dulcitol, salicin, ethyl alcohol, sodium tartrate, hippuric acid, malonic acid and sodium citrate as carbon sources.

All the species of Fusarium hydrolyzed starch and utilized the ammonium ion, urea, peptone, proteose-peptone and asparagin as nitrogen sources. None produced indol from tryptophane nor hydrogen sulfide from sulphur-containing proteins. Gelatin was liquefied by all isolates, pectate reduced and precipitation of casein and peptonization occurred in milk cultures. The addition of thiamin to a synthetic medium did not affect growth rate to any marked degree.

The use of organic dyes as growth-inhibiting substances showed some promise as a tool in the diagnosis of species. Actidione and various concentrations of sodium chloride and glucose showed little differential action as growth-inhibiting substances. The plant extract from Valiant tomato plant did, however, inhibit the growth of F. oxysporum conglutinans on nutrient agar and in that respect some differential action appeared.

An examination of the host plants in fungal filtrates shows that both Pan American and Bonny Best plants wilted only slightly in the cabbage Fusarium filtrate. Bonny Best had not begun to exhibit symptoms in the F. oxysporum conglutinans filtrate after 48 hours although black necrotic spots began to appear in 60 hours. With the exception of a faint orange color developed on the synthetic agar used in the vitamin B₁ experiment the cabbage organism failed to produce pigment on any of the media used in the study. The inhibition of the cabbage Fusarium organism on a nutrient medium containing extract from a tomato plant indicates a possible method to be used in the diagnosis of species. The lack of wilting by tomato plants in the cabbage Fusarium filtrate also suggests a field for future investigation.

A comparison of the physiological characters exhibited by the Fusarium forms of this study indicates the possibility that further work may supply a basis for differentiating at least the cabbage strain of Fusarium from some of the other forms in the Elegans group.