Prometryn Tolerance in Glanded versus Glandless Isolines of Cotton

Abstract

Cotton (Gossypium hirsutum L.) cultivars normally have lysigenous glands conditioned by two dominant, independently inherited alleles, Gl2 and Gl3. Glandless (gl2gl2gl3gl3) isogenic lines are now available for a number of those cultivars. Such lines allow a decisive test for the relationship formerly proposed between accumulation of the herbicide prometryn [N,N′‐bis(1‐methylethyl)‐6‐(methylthio)‐l,3,5‐triazine‐2,4‐diamine] in the lysigenous glands and increased crop tolerance to that pesticide. Experiments were conducted in a growth chamber to compare the prometryn tolerance of glanded vs. glandless ‘Empire 61 (WR)’ and ‘Westburn M’ isolines. Two intermediately glanded Empire isolines (Gl2Gl2gl3gl3 and gl2gl2Gl3Gl3) 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 than in glandless plants within the same genetic background. Comparisons involving the intermediately glanded Empire isolines sugo gested that Gl2 enhances seedling tolerance more than does Gl3. Glanded vs. glandless isolines in five genetic backgrounds (i.e., Empire 61 (WR), Westburn M, ‘Delcot 277’, ‘TH 149’, and ‘Stoneville 213’) plus the two intermediate Empire isolines were also evaluated for prometryn tolerance in the field. Visual crop injury ratings and measured lint yields support the growth chamber data. The treated glanded isoline on each background displayed less injury (20–56%) and higher yield (44–60%) than the corresponding glandless isoline. Again, Gl2 showed less injury than Gl3 though differences in lint yield were not significant. Clearly, lysigenous glands enhance prometryn tolerance in cotton, and higher gland density is directly associated with higher photosynthetic rates and reduced crop injury.