SOMATIC EMBRYOGENESIS AND CALLUS PRODUCTION FROM COTYLEDON EXPLANTS OF EASTERN BLACK-WALNUT

Starting at 8 weeks and continuing until 23 weeks (nut drop) after anthesis, 1 cm2 explants from cotyledons of immature seeds were extracted from Juglans nigra fruits. Explants were placed on Woody Plant Medium with 1 g l-1 casein hydrolysate and 30 g l-1 sucrose. The explants remained in light for 4 weeks on primary media containing a 3 X 3 factorial of 0.05, 0.5, or 5.0 muM thidiazuron (TDZ) and 0.1, 1.0, or 10.0 muM 2,4-D. Explants were transfer-red to a secondary medium containing no plant growth regulators and incubated in darkness for 11 weeks. The greatest number of somatic embryos was produced 8, 10, and 12 weeks after anthesis from explants on media with 0.5 or 5.0 muM TDZ and 0.1 or 1.0 muM 2,4-D. Explants produced the greatest callus volume and dry weight 10, 12, and 14 weeks after anthesis. Throughout the study, callus generally increased with increasing concentrations of both TDZ