Submitted to: Canadian Journal of Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 30, 2012
Publication Date: February 1, 2013
Repository URL: http://handle.nal.usda.gov/10113/55912
Citation: Funnell-Harris, D.L., Prom, L.K., Pedersen, J.F. 2013. Isolation and characterization of the grain mold fungi, Cochliobolus and Alternaria spp., from sorghum using semi-selective media and DNA sequence analyses. Canadian Journal of Microbiology. 59(2): 87-96. Interpretive Summary: One limitation to grain sorghum production is mold disease caused by fungi in the groups Fusarium, Alternaria and Cochliobolus. Improved methods to isolate and characterize these fungi were needed. Two semi-selective agar media were developed and compared to previously used media. The new media were found to be as good or superior to isolate these fungi from sorghum grain.
Technical Abstract: Mold diseases, caused by fungal complexes including Alternaria, Cochliobolus and Fusarium species, limit sorghum grain production. Media were tested by plating Fusarium thapsinum, Alternaria sp. and Curvularia lunata, individually and competitively. Dichloran chloramphenicol rose bengal (DRBC) and modified V8®-juice (ModV8) agars, found to be useful, were compared to commonly-used agar media, dichloran chloramphenicol peptone (DCPA) and pentachloronitrobenzene (PCNB). Radial growth, starting with mycelia, or single-conidia and hyphal tips, demonstrated an effect of media. For isolation of grain fungi, DRBC and ModV8 were similar or superior to DCPA and PCNB. When seedlings were inoculated with conidia of C. lunata, Alternaria sp., F. thapsinum, or mixtures, percent root infection ranged from 28% to 77%. For mixed inoculations, shoot weights, lesion lengths and percent root infections were similar to F. thapsinum inoculations; most colonies recovered from roots were F. thapsinum. For Alternaria grain isolates, five morphological types, including Alternaria alternata, were distinguished by colony morphologies and conidial dimensions. Sequence analysis using a portion of the endo-polygalacturonase gene was able to further distinguish isolates. Cochliobolus isolates were identified morphologically as C. lunata, Curvularia sorghina and Bipolaris sorghicola. Multiple molecular genotypes were apparent from rRNA internal transcribed spacer region sequences from Cochliobolus grain isolates.