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Mechanisms Associated with the tr Allele Contributing to Reduced Smut Susceptibility of Pearl Millet. Jeffrey P. Wilson, Research Plant Pathologist, USDA-ARS Forage and Turf Research Unit, University of Georgia Coastal Plain Experiment Station, Tifton 31793-0748; Phytopathology 85:966-969. Accepted for publication 25 May 1995. 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, 1995. DOI: 10.1094/Phyto-85-966.

The tr allele in pearl millet confers trichomeless plant structures. Plants homozygous for the allele have reduced severities of smut, caused by Moesziomyces penicillariae, compared to plants with the Tr genotype. Experiments were conducted to determine the mechanisms conferring reduced susceptibility in trtr inbreds. Flag leaf sheaths of field-grown Tift 23DAS (trtr) were wrapped around unemerged panicles more tightly than were sheaths of Tift 23DA (TrTr), as measured by reduced infiltration of fluid into the boot, recovery of sporidia of M. penicillariae from unopened boots, and smut severity of panicles bagged prior to emergence from the boot. When exposed panicles were inoculated with M. penicillariae in the greenhouse, moisture periods required for a given level of smut severity were greater for Tift 23DAS than for Tift 23DA. Severity after 8 h of moisture was greater on Tift 23DA. Increase of disease severity with longer moisture periods was essentially linear and parallel for both inbreds for moisture periods of up to 48 h. Intercepts (severity at 8 h) differed, but slopes did not. The tr allele may be useful as an easily identifiable, monogenic marker for smut resistance in pearl millet.