( Sorghum bicolor
L. Moench) plant pigments have been associated with resistance to leaf diseases and grain deterioration. Four near-isogenic pairs of tan and non-tan (red) sorghum lines were assayed for their phenolic content and evaluated for their reaction to leaf diseases along with six other sorghum lines. Leaves, stems, sheaths, glumes and seeds of mature plants were assayed for tannins, pigments, and precursors of these pigments. No tannins were detected in the various plant tissues although other genotypes can have high levels of these compounds in seed coats. The red plants (especially the glumes and sheath) were found to accumulate 3-deoxyanthocyanidins, the major pigments in sorghum, but these were absent in the tan plants. The glumes and sheath of tan plants accumulated apigenin. Near-isogenic pairs were tested for differential reactions to anthracnose ( Colletotrichum graminicola
Ces.) at Tifton, Georgia and to rust ( Puccinia purpurea
Cooke) at Isabella, Puerto Rico during the 1991 growing season. Tan and red isogenic pairs, which differ significantly in phenolic composition, did not show significant differences in their disease reaction. The six other sorghum lines which showed marked differences in their reaction to leaf diseases also showed differences in their phenolic composition. However, for the phenols that were analyzed, there was no correlation with resistance or susceptibility. It is proposed that tannins, pigments, and pigment precursors are not responsible for disease resistance in these genotypes.