HERBICIDE GLYPHOSATE AT SUBLETHAL CONCENTRATIONS ENHANCES SOMATIC EMBRYO DEVELOPMENT IN SWEET-POTATO (IPOMOEA-BATATAS L.)

Herbicide glyphosate, when included at sub-lethal levels in the tissue culture medium with other growth regulators, enhanced somatic embryo production in sweetpotato (Ipomoea batatas L,), The leaf explants of t he genotype PI 318846-3 were incubated in the dark for two weeks on MS medium containing 2,4-D (2.5 mg/l) and BAP (0.25 mg/l), and transferr ed to a medium containing abscissic acid (ABA; 2.5 mg/l) and glyphosat e (0, 20, 40, 80, 100, and 200 mu M), Somatic embryos developed earlie r and matured faster (by 10 days) on explants cultured on glyphosate ( 200 mu M) than those cultured on ABA alone (control), Explants treated with 200 mu M glyphosate produced a large number of embryos (26 per e xplant) compared to the control (2.5 per explant), and germinated at a higher frequency, Embryogenic calli resulting from the glyphosate tre atment appeared desiccated and the resulting somatic embryos showed a marked reduction in precocious germination, When transferred to a medi um with 20 mg/l of gibberellic acid (GA,), embryos initiated on the 10 0 mu M glyphosate medium converted to plantlets at a higher rate (70%) than those from control (24%), Glyphosate supplement thus appears to promote the somatic embryo production in sweetpotato by enhancing the maturation, germination and conversion of embryos possibly by promotin g desiccation, an essential step for embryo quiescence, Other possible reasons for the promotive role of glyphosate in sweetpotato somatic e mbryo development are discussed.