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Comparison of Sorghum Seedling Reactions to Sporisorium reilianum in Relation to Sorghum Head Smut Resistance Classes. J. Craig, Research Plant Pathologist, Agricultural Research Service, U.S. Department of Agriculture, College Station, TX. R. A. Frederiksen, Professor, Department of Plant Pathology and Microbiology, Texas A&M University, College Station 77843. Plant Dis. 76:314-318. Accepted for publication 29 August 1991. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1992. DOI: 10.1094/PD-76-0314.

Seedlings of sorghum genotypes resistant and susceptible to Sporisorium reilianum were grown in peat pellets and inoculated by infesting vermiculite surrounding seedling epicotyls with 7- to 10-day-old teliospore cultures. Four days after inoculation, the seedlings were removed from the pellets, placed in test tubes containing water deep enough to completely submerge the first leaf, and incubated in darkness at 24 C for 5 days. After incubation, symptoms on the first leaf blade differentiated susceptible and resistant genotypes. Symptoms on the first leaf blades of susceptible genotypes were general chlorosis and brown spots. Leaf symptoms of resistant genotypes consisted of interveinal chlorosis and an absence of brown spots on the leaf blade. The inoculation and incubation procedures described in this study will identify types of head smut resistance that prevent the pathogen from reaching the apical meristem of the sorghum plant. This type of resistance appears to be effective against the variability in virulent biotypes of S. reilianum that has overcome the race-specific head smut resistance factors deployed in the past.

Keyword(s): horizontal resistance.