ABSTRACT
Cotton (Gossypium hirsutum L.) cultivars normally have lysigenous glands conditioned by two dominant, independently inherited alleles, Gl(2) and Gl(3). Glandless (gl(2)gl(2)gl(3)gl(3)) isogenic lines for a number of those cultivars have been developed for various purposes and are now available. Such lines allow a decisive test for the relationship formerly proposed between accumulation of the herbicide prometryn [N,N'-bis(1-methylethyl)-6-(methylthio)-1,3,5-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 (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 fluorescence measurement curves established that the photosynthetic inhibition caused by prometryn in glanded plants was of less intensity and shorter duration than in glandless plants. Comparisons involving the intermediately glanded Empire isolines suggested that Gl(2) enhances tolerance more than does Gl(3). Glanded vs. glandless isolines on 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 injury ratings and measured lint yields support the growth chamber data. The treated glanded isoline on each background displayed less injury (20 to 56%) and higher yield (44 to 60%) than the corresponding glandless isoline. Again, Gl(2) showed less injury than Gl(3) though differences in lint yield were not significant. Clearly, lysigenous glands enhance prometryn tolerance in cotton, and higher gland density is directly associated with increased tolerance.
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