PROMETRYN TOLERANCE IN GLANDED VERSUS GLANDLESS ISOLINES OF COTTON

Cotton (Gossypium hirsutum L.) cultivars normally have lysigenous glan ds conditioned by two dominant, independently inherited alleles, Gl(2) and Gl(3). Glandless (gl(2)gl(2)gl(3)gl(3),) isogenic lines are now a vailable for a number of those cultivars. Such lines allow a decisive test for the relationship formerly proposed between accumulation of th e herbicide prometryn lethyl)-6-(methylthio)-1,3,5-triazine-2,4-diamin e] in the lysigenous glands and increased crop tolerance to that pesti cide. Experiments were conducted in a growth chamber to compare the pr ometryn tolerance of glanded vs. glandless 'Empire 61 (WR)' and 'Westb urn M' isolines. Two intermediately glanded Empire isolines (Gl(2)Gl(2 )gl(3)gl(3) and gl(2)gl(2)Gl(3)Gl(3)) were also available for analysis . Ratios derived from leaf chlorophyll fluorescence measurement curves established that the photosynthetic inhibition caused by prometryn in glanded cotton seedlings was of less intensity and shorter duration t han in glandless plants within the same genetic background. Comparison s involving the intermediately glanded Empire isolines suggested that Gl(2) enhances seedling tolerance more than does Gl(3). Glanded vs. gl andless isolines in five genetic backgrounds (i.e., Empire 61 (WR), We stburn M, 'Delcot 277', 'TH 149', and 'Stoneville 213') plus the two i ntermediate Empire isolines were also evaluated for prometryn toleranc e in the field. Visual crop injury ratings and measured lint yields su pport the growth chamber data. The treated glanded isoline on each bac kground displayed less injury (20-56%) and higher yield (44-60%) than the corresponding glandless isoline. Again, Gl(2) showed less injury t han Gl(3) though differences in lint yield were not significant. Clear ly, lysigenous glands enhance prometryn tolerance in cotton, and highe r gland density is directly associated with higher photosynthetic rate s and reduced crop injury.