Induction of embryogenic Triticum aestivum L. calli. II. Quantification of organic addenda and other culture variable effects

Abstract

Nine experiments were conducted to determine effects of various culture medium addenda on inducation of embryogenic calli from immature embryos of a responsive Triticum aestivum L. genotype (PCYT 10). Effects were quantified by counting somatic embryos (embryoids) per callus. Optimal auxin concentrations to induce and maintain somatic embryogenesis were 3.62 μM 2,4-dichlorophenoxyacetic acid (2,4-D) or 9.05 μM 3,6-dichloro-o-anisic acid (dicamba). In general, dicamba permitted formation of significantly more embryoids than 2,4-D. Kinetin (6-furfurylaminopurine) at 2.56 μM or 4.65 μM significantly increased percentage scutellar callus when added to 2,4-D or dicamba-containing medium, respectively. Kinetin at 4.65 μM significantly increased the numbers of embryoids formed when added to medium containing either synthetic auxin. Significantly fewer embryoids formed when cultures were incubated under diffuse light (16-h photoperiod). Casein hydrolysate (200 mg1^-1) or L-arginine (0.23 mM) had no effect on numbers of embryoids formed, whereas L-tryptophan (0.20 mM) enhanced such formation with 2,4-D and decreased such formation with dicamba. Two additional experiments generally demonstrated that response to auxin source in the genotypes ND 7532, PCYT 20, Yaqui 50, and Oasis was similar to that in PCYT 10. The higher molar concentration of dicamba required to induce embryogenic callus coupled with more evident embryoid precocious germination and a more rapid rate of tissue necrosis upon extended incubation without subculture suggests that dicamba is metabolized more rapidly than 2,4-D in T. aestivum callus cultures.