Differential Varietal Tolerance of Peach(Prunus persica)Seedlings to Glyphosate

Abstract

The translocation and effects of glyphosate [N-(phosphonomethyl)glycine] were determined in greenhouse-grown peach [Prunus persica(L.) Batsch] seedlings obtained from different seed parents. Two lower branches of 10-week-old seedlings of Rutgers Red Leaf, Bailey, Kalamazoo, Siberian C, and Harrow Blood were sprayed with 0.9 to 18 mg of glyphosate per plant. Seedlings of Harrow Blood, Bailey, and Kalamazoo were more susceptible to injury than were those of Siberian C and Rutgers Red Leaf. Glyphosate at 6, 9, and 18 mg produced necrotic areas on the stems of the former seedlings and at the higher rates tree death resulted. The Siberian C and Rutgers Red Leaf seedlings showed only chlorosis and malformation of apical leaves although slight stem injury occurred 1 month after treatment. Measurements of plant weight, height, and stem diameter indicated that seedlings of Harrow Blood, Bailey, and Kalamazoo tolerated only 3 mg of glyphosate without growth reduction. This was one-half and one-third of the amount which seedlings of Siberian C and Rutgers Red Leaf tolerated, respectively. The concentration of glyphosate in the treated lower branches and the main stem of the seedlings was determined by thin-layer chromatography. The concentrations in the bark were generally similar among all seedlings. Differential tolerance, therefore, was not based on differences in overall glyphosate concentration in tissues but on protective or resistance mechanisms present only in seedlings of Siberian C and Rutgers Red Leaf.