Pathogenicity of Fusarium graminearum isolates on maize (Zea mays L.) cultivars and relation with deoxynivalenol and ergosterol contents

Fusarium graminearum is an important pathogen of maize and causes seed rot and seedling blight as well as root rot, stalk rot and ear rot. In growth chamber experiments, inoculation of corn cv. 'Loyal' seeds with six different F graminearum isolates reduced emergence of germlings and caused seedling death of varying degrees. Seedling blight and root rot caused by F. graminearum isolates were determined by using an aeroponics system. This system allows non-destructive, repetitive sampling of seedlings for assessing disease progress and seedling growth. Following inoculation of 10-day-old seedlings by dlipping the root system in a conidia-mycelium suspension and cultivating the seedlings in the nutrient aeroponics system, the F, graminearum isolates differed significantly in root rot severity and seedling dry weight of corn cv. 'Loyal'. Six isolates of F. graminearum were also tested for their stalk rot pathogenicity at maturity stage under greenhouse and field conditions using the toothpick inoculation method. Stalk rot symptoms were produced by all isolates, but the isolates differed in their degree of pathogenicity. The corn cultivars reacted differently to the infection by the F. graminearum isolates. While cv. 'Loyal' was the most susceptible, cv. 'Galice' exhibited the highest level of resistance. The cvs. 'Unico' and 'Marshall' showed a moderate degree of resistance. Beside the seedling blight index, deoxynivalenol (DON) concentrations and ergosterol contents were determined in corn seedling tissue. All isolates tested were able to produce DON in infected seedling tissue. There was a close relationship between the degree of disease severity and DON concentration. On the other hand, a relation between disease severity and ergosterol content in the infected seedling tissues could not be detected.