FATE OF PROMETRYN IN PROMETRYN-TOLERANT AND PROMETRYN-SUSCEPTIBLE COTTON CULTIVARS

Prometryn is a soil-applied herbicide used in cotton production; howev er, it can cause cotton injury. Our objective was to determine the mec hanism of differential tolerance among cultivars as related to differe nces in prometryn absorption, translocation to photosynthetic tissue o r lysigenous glands, and metabolism. The prometryn-tolerant cultivars, Pima S-7 (Gossypium barbadense L.), a Pima-type cotton, and Acala 151 7-75 (G. hirsutum L.), an Upland-type cotton, were compared to the pro metryn-sensitive Upland-type cultivars, Delta Pine 5415 (G. hirsutum) and Acala 2711 glandless (G. hirsutum). Uptake and metabolism of prome tryn by excised tissue in solution, uptake and translocation of promet ryn by roots or hypocotyls in whole plants in soil, and the concentrat ions of prometryn in lysigenous glands in whole plants were compared a mong the cultivars. In the excised tissue study, root tissue absorbed more prometryn than did excised hypocotyl tissue over 2 hr for all cul tivars; Pima S-7 root and hypocotyl tissue absorbed more prometryn tha n Acala 1517-75 or Delta Pine 5415 over time, and no metabolites of pr ometryn were found in any of the tissues. In the whole-plant study whe re roots or hypocotyls were exposed to prometryn in soil, prometryn ro ot uptake by Delta Pine 5415 was lower than by Pima S-7 or Acala 1517- 75, while hypocotyl uptake and translocation did not differ among cult ivars. Therefore, differential prometryn tolerance among these cultiva rs cannot be explained by differences in uptake or translocation. Howe ver, uptake and translocation were greater in root-treated compared to hypocotyl-treated seedlings, regardless of cultivar, over time. Lysig enous glands contained higher levels of prometryn relative to other st em tissue; however, the amount of prometryn in glands was no greater i n susceptible Delta Pine 5415 than in tolerant Pima S-7. Thus, differe ntial prometryn tolerance in these cotton cultivars is not due to diff erential prometryn absorption, translocation, metabolism, or concentra tion in lysigenous glands. (C) 1996 Academic Press.