Inoculation strategies to assess biological interactions between Fusarium and Alternaria species infecting sorghum

New cultivars of sorghum are being developed for increased food use, as livestock feed, and for the bioenergy industry by manipulation of secondary metabolic pathways through breeding. Previous work has suggested that such modifications may have an impact on cultivar response to fungal pathogens. We investigated four inoculation strategies that may be used in studies involving pathogens of sorghum. Plants of elite sorghum genotypes ‘Wheatland’ and RTx430, commonly used in breeding programs, were inoculated with isolates of Alternaria alternata, Fusarium equiseti, Fusarium proliferatum, Fusarium solani, Fusarium thapsinum, and Fusarium verticillioides recovered from field-grown sorghum. Wound inoculation of the peduncles of heads at anthesis demonstrated that isolates of F. verticillioides and F. thapsinum produced mean lesion lengths that were significantly greater than control inoculations. The length of this assay was decreased by inoculating fungi onto plants of a very early maturing sorghum line (N247). Spraying heads at anthesis with conidial suspensions over three consecutive days in the greenhouse was conducted to attempt to mimic conditions in the field. Results indicated that plants treated with conidia of F. thapsinum may develop mature grain with reduced germination. Seed and seedling inoculations produced responses over a relatively short time period. Seed inoculations were conducted in a manner similar to a corn bioassay. Seedling inoculations, conducted in Magenta vessels, allowed for measurement of effects of inoculum on roots, stalks, and leaves. Following inoculation of RTx430 and ‘Wheatland’ plants grown in Magenta vessels with F. thapsinum, nearly all measurements were significantly different from those of the water controls except for percent root infection of RTx430.