Effect of haloxyfop and fluazifop on morphology and fatty acid synthesis of annual blue grass (Poa annua L.) seedlings.

Abstract

Haloxyfop-methyl, methyl-2-[4-[[3-chloro-5-(triflouromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid] and fluazifop-butyl, (+)-butyl-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy]phenoxy]propanoic acid are used for selective control of annual and perennial gramineous weeds in broadleaf crops. Annual blue grass (Poa annua L.) is controlled by haloxyfop-methyl but not by fluazifop-butyl. Research was conducted to determine the effect of each herbicide on growth, morphology, lipid synthesis and acetyl-CoA carboxylase activity, of this species, and to determine physiological mechanism of annual blue grass tolerance to fluazifop-butyl. Techniques used in this research were growth measurements, light and electron microscopy, TLC, and enzyme assay for acetyl-CoA carboxylase. Haloxyfop-methyl at 15 μM when applied preemergence caused 96% reduction of root growth of annual blue grass whereas fluazifop-butyl at 15 μM caused 42% reduction of root growth. Haloxyfop-methyl at 5 μM and 15 μM caused 35 and 96% inhibition of leaf growth, respectively. Fluazifop-butyl at same rates caused 19 and 32% inhibition of leaf growth. Haloxyfop-methyl at 5 and 20 μM when applied postemergence caused 20 and 56% reduction of leaf growth, respectively. Fluazifop-butyl at same rates caused 11 and 21% reduction of leaf growth. Haloxyfop-methyl at 20 μM caused 80% reduction of annual blue grass seedlings dry weight whereas fluazifop-butyl caused 40% reduction. Morphological studies showed that postemergence applications of 20 μM of haloxyfop-methyl caused severe tissue injury whereas same rates of fluazifop-butyl caused less injury. Ultrastructural studies showed that haloxyfop-methyl at 20 μM caused disruption, elongation, and reduction of chloroplast thylakoids whereas fluazifop-butyl caused less injury to thylakoids. Acetyl-CoA carboxylase activity from annual blue grass was inhibited by about 40% in the presence of 10 μM haloxyfop acid but fluazifop acid caused 6.5% inhibition. The lipid content was reduced by 56% in seedling treated with 20 μM haloxyfop-methyl whereas fluazifop-butyl caused 19% inhibition. Fluazifop-butyl at all rates caused no loss of lipid classes whereas haloxyfop-methyl at 10 and 15 μM caused loss of phospholipid and glycolipid which are part of the cellular membranes. Haloxyfop caused greater reduction of leaf and root growth, greater degree of tissue injury and chloroplast distortion, greater inhibition of acetyl-CoA carboxylase activity than fluazifop. All these effects lead to degradation of cellular components and eventually to the death of the plant.