Absorption, translocation, and fate of herbicides in Orobanche cumana–sunflower system

Abstract

The absorption and translocation of [ 14 C ]pronamide, [ 14 C ]glyphosate, and [ 14 C ]imazapyr and the metabolism of [ 14 C ]imazapyr, were studied in the Orobanche cumana–sunflower system. [ 14 C ]Pronamide was applied as a sunflower seed treatment by coating or soaking. Herbicide absorption was affected by method of seed treatment, but not the subsequent pattern of herbicide distribution within the sunflower plant. Herbicide absorption by the seed was 9.8 and 3.4%, respectively. The translocation of the radioactive herbicide from the treated seed to the rest of the plant was greater for the coating than for the soaking treatment, regardless of the presence or absence of parasitic plants. The leaves were the sunflower component in which larger amount of [ 14 C ]pronamide was detected, reaching up to 3.24 and 2.45% for the coating application and the non-infested and infested sunflower, respectively. Translocation of the herbicide from the root system of the host plant to the parasitic plant was 0.61 and 0.21% for the coating and soaking treatments, respectively, in infested sunflower. [ 14 C ]Glyphosate and [ 14 C ]imazapyr were applied as a post-emergence treatment to sunflower, whether it was parasitized by O. cumana or not. Glyphosate translocation within the host plant did not differ between O. cumana-infested and non-infested plants and most of the radioactivity remained in the treated leaf. Translocation of [ 14 C ]glyphosate to O. cumana reached 5.5% at 3 DAT. The absorption of [ 14 C ]imazapyr by the treated leaf was greater than [ 14 C ]glyphosate absorption at 1 DAT. Similarly, higher levels of imazapyr were accumulated by O. cumana from the treated leaf. The metabolism study of [ 14 C ]imazapyr showed a constant presence of imazapyr in the treated leaf at 16%, but in O. cumana the parent compound was 51.4% of the total recovered radioactivity 6 DAT. The deposit of imazapyr in O. cumana and the low metabolism in this species may explain the control of O. cumana by this herbicide.