The Inhibition of Fungal Growth in Resistant Cotton Plants Infected by Fusarium oxysporum f. sp. vasinfectum

The vascular colonization of cotton plants by Fusarium oxysporum f. sp. vasinfectum was determined by examining growth of the fungus from free-hand cross sections taken from 0 to six days after inoculation at various distances above the points of root inoculation. Fungal spread in both longitudinal and lateral directions in the susceptible cultivar Rowden was evident four days after inoculation, whereas fungal spread in the resistant cultivar Seabrook Sea Island was restricted. The quantity of viable fungus in infected tissues was determined from macerated tissues plated on Czapek- Dox agar. The colony counts declined within six days after inoculation in resistant Seabrook Sea Island, but not in susceptible Rowden, implying that an inhibition of fungal growth in vascular tissues occurred in resistant Seabrook Sea Island. This inhibition could contribute to the restriction of fungal spread and thus be a factor in the resistance of cotton plants to F. oxysporum f. sp. vasinfectum .