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Effects of Alachlor and Glyphosate on Development of Glomus Mosseae and its Symbiotic Association with Peanut
Abstract:
This study aimed to evaluate the effects of alachlor (soil-acting herbicide) and glyphosate (foliage-acting herbicide) on Glomus mosseae (vesicular-arbuscular mycorrhiza fungus) growth phases directly and indirectly on its symbiotic association with peanut. Laboratory experiment was carried out to determine the effects of herbicides on spore germination and hyphal growth of G. mosseae. The recommended rates of alachlor for soil and water agar media are 3.6 μg ai g-1 soil and 24 μg ai mL-1 agar, and for glyphosate, 2.16 μg ae g-1 and 14 μg ae mL-1 agar, respectively. Alachlor at tenfold of the recommended rate significantly (p ≤ .01) reduced spore germination of G. mosseae by 36 and 43 percent, and hyphal length was reduced by 61 and 83 percent in soil and water agar media, respectively. The application of alachlor at tenfold of the recommended rate (36 μg ai g-1) reduced the length of active external hyphae of G. mossaeae by 40 percent (23.99 cm g-1). Alachlor at one and a half of the recommended rate (5.4 μg ai g-1) decreased the development and succinate dehydrogenases (SDH) activity of internal hyphae of G. mosseae and the amount of mycorrhizal tissue. In contrast, glyphosate at all rates had no negative effect on spore germination and hyphal length of G. mosseae in both soil and water agar media, and also did not affect the external and internal hyphae.
The effect of herbicides on G. mosseae symbiosis with peanut was also studied in the greenhouse. The adverse effects of alachlor on the mycorrhizal plants were greater than in nonmycorrhizal plants. The phosphorus concentration in the shoot was unaffected by alachlor in the nonmycorrhizal plant or by glyphosate in the mycorrhizal plant and vice versa. Alachlor and glyphosate did not affect P inflow into nonmycorrhizal plants. However, P inflow into mycorrhizal plant was increased by glyphosate application at 2.16 μg ae g-1, which gave 65.31 × 10-13 mol P m-1 s-1. It increased hyphal inflow of 41.48 × 10-13 mol P m-1 s-1, and consequently increased hyphal uptake from soil to be 479.72 from 48.04 × 10-13 mol P m-1 s-1 in control. The effect of G. mosseae on the persistence and degradation of herbicides in the soil showed that the rate of degradation of alachlor was higher in G. mosseae inoculated soil than in the uninoculated soil. Therefore, the persistence of alachlor in the soil was shortened by six days with the presence of G. mosseae. However, the persistence of glyphosate in the soil was unaffected by the presence of fungi.
Results of the study showed that the type of herbicides and their rates are important factors mediating the effects of herbicides on G. mosseae and its symbiosis with peanut plant. The distinct growth phases of G. mosseae may differ in their tolerance to alachlor herbicide. There was interaction between alachlor and G. mosseae, which was indicated by the adverse effect on mycorrhizal plants, and evidence that the persistence of alachlor in the soil was shortened by the fungi. In contrast, glyphosate did not affect the growth phases of G. mosseae.
