Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2008
Publication Date: 11/7/2008
Citation: Funnell-Harris, D.L., Pedersen, J.F. 2008. Inoculation strategies to assess biological interactions between fusarium and alternaria species infecting sorghum. Canadian Journal of Plant Pathology 30: 404-413. Interpretive Summary: Three bioassays were evaluated for their ability to characterize fungal species for their ability to cause diseases in sorghum [Sorghum bicolor (L.) Moench] or to screen sorghum plants for disease resistance. Improved screening methods were developed that can be used in sorghum research and isolates of the fungi Fusarium thapsinum, Fusarium verticillioides and Alternaria alternata were shown to be potentially pathogenic on sorghum.
Technical Abstract: Three bioassays were assessed for experimental utility to either characterize fungal species potentially pathogenic to sorghum [Sorghum bicolor (L.) Moench] or to screen germplasm for advancement in breeding programs. Isolates of species commonly associated with sorghum, Alternaria alternata, Fusarium equiseti, F. solani, F. thapsinum and F. verticillioides, were tested in different bioassays. Bioassays included wound-inoculation, spray inoculation of developing heads and inoculation of sterile plants. A well-utilized bioassay in which peduncles of developing heads were wound-inoculated indicated that isolates of F. thapsinum (FRC-M-3790) and F. verticillioides (FRC-M-1141) were pathogenic and that an isolate of A. alternata (H02-755S) also may be pathogenic on certain lines. It was demonstrated that the duration of this assay could be abbreviated by inoculation of an early-maturing sorghum line (N247). Spray inoculation, which may more closely mimic natural conditions, had inconsistent results: in one assay, weight per 100 seed and percent germination suggested that FRC-M-3790 and FRC-M-1141 may be pathogenic but in other assays, there were no biologically relevant differences among inocula treatments. In a seedling assay, stalk lesion length following infection of plants without wounding and percent infection of excised root pieces indicated that isolate FRC-M-3790 was an aggressive pathogen. The seedling assay indicated whether a potential pathogen infected roots and/or the stalk and allowed characterization of symptoms on roots. This study emphasizes the importance of selection of appropriate plant lines for characterization of fungal virulence traits. The use of known highly virulent and low virulence isolates when screening germplasm is suggested as well.