Inhibition of Electron Transport Rate in Cotton and Weeds By Ammonium Glufosinate

The cotton is one of the most important fiber crops in the world. Glufosinate is an important herbicide for cotton crop, with broad-spectrum action, non-selective and applied post-emergence. Herbicide molecules act on plant physiology and may inhibit enzymes responsible for secondary compounds vital to plant development. The present study aimed to evaluate the effect of glufosinate on the electron transport rate of photosystem II in cotton and weeds. Cotton plants (cultivar FiberMax 910), Urochloa decumbens and Ipomoea grandifolia were cultivated in five-liter pots filled with substrate. The trial was conducted in a completely randomized design with four replicates. The treatments consisted of the application of ammonium glufosinate (2.0 L p.c. ha^-1) and five periods without rainfall: 1, 3, 6, 24 and 48 h after application and a control treatment (without application). The evaluations of photosystem II electron transport rate (ETR) were performed at 0, 1, 2, 3, 4, 5, 6, and 7 days after application (DAA). Data were subjected to analysis of variance and the means were compared by Tukey test at 5% probability. For cotton, there was a greater inhibition of ETR in the treatment 48 h without rain at 1 DAA and, at 8 DAA, there was an inhibition of ETR greater than 95% for all the treatments. For U. decumbens, an inhibition of ETR greater than 50% was observed for all treatments at 2 DAA, reaching 98% inhibition at 8 DAA. In I. grandifolia, at 2 DAA, all treatments promoted inhibition of ETR greater than 70% and, at 8 DAA, the inhibition was greater than 80% for all treatments. It was concluded that the amount of herbicide absorbed 1 hour after application is enough to promote inhibition of ETR in cotton plants, as well as in U. decumbens and in I. grandifolia.