The histology and morphology of developing asparagus Asparagus officinalis L.) somatic embryos arising in callus cultures were examined and contrasted with that documented for zygotic embryos. Histological sections of lateral bud-derived callus cultured for 2 weeks on embryo induction medium consisting of Murashige and Skoog salts and vitamins (MS) with 1.5 mg NAA/liter and 0.1 mg kinetin/liter indicated the formation of distinct groups of embryogenic cells. At 4 weeks, the callus was comprised of embryos in the early and late globular stages and a few bipolar embryos. Within 2 weeks on embryo development medium consisting of MS with 0.05 mg NAA/liter and 0.1 mg kinetin/liter, the globular embryos developed a bipolar shape having an expanded upper region that formed the cotyledon and a smaller region that formed the radicle. Within 4 to 6 weeks on this latter medium, each mature bipolar embryo was opaque and had a large cotyledon, a distinct shoot apex at the cotyledon-hypocotyl junction, and vascular connections between the radicle, shoot apex, and cotyledon. Many mature somatic embryos resembled the asparagus zygotic embryos in having a crescent shape, whereas others had a short but wide cotyledon. Both somatic embryo types converted to plantlets at equal rates. Chemical names used: N- (2-furanylmethyl)-1 H -purin-6-amine (kinetin); 1-naphthaleneacetic acid (NAA).
A. Levi and K.C. Sink
T. Ball, J. Smeenk, and K.C. Sink
Outstanding asparagus crowns were identified in established Michigan asparagus fields, MSU germplasm, variety trials, or were provided by commercial sources. The single-crown selections were micropropagated to provide cloned plants for the trials. Field trials consisting of four replications of 12 plants each were established at two locations. Crowns were planted 8 inches deep and spaced 18 inches apart in rows 4.5 or 5 feet apart. Five, 37, and 25 selections were planted in 1998, 1989, and 1991, respectively. Plots were not harvested until 2 years after planting, when they had partial harvests of six pickings. In the third and following years, plots received full harvests of 20 to 25 pickings. In the third full harvest at the Hart location, clones Hart-2 and Hart-3 yielded 6989 and 6875 lb/A, respectively, and were significantly more productive than Syn4-56, which had 3720 lb/A. At Benton Harbor, Hart-4 produced 4184 lb/A, significantly higher than the Syn4-56 yield of 3088 lb/A at that location. These significant differences were not observed until the second full harvest.
P.F. McCabe, L.J. Dunbar, A. Guri, and K.C. Sink
Sexual hybrid plants of Lycopersicon esculentum × L. pennellii (E × P) have been transformed and the T-DNA inserts genetically mapped. Donor protoplasts of E × P were isolated from leaves, and subsequently irradiated with 0, 5, 10 and 20 krad of a 60Co. They were then fused with suspension-derived protoplasts of S. lycopersicoides using the PEG-CA++-high pH technique. The protoplasts were cultured in medium 8E at 1.5 × 106 protoplasm/ml. Selection of heterokaryon-derived macrocalli was facilitated by the inability of irradiated donor protoplasts to divide and by plating p-calli on regeneration medium containing kanamycin - an antibiotic for which the resistance gene NPTII is part of the T-DNA. Morphological characteristics of the resulting asymmetric somatic hybrid plants indicate that 10 and 20 krad irradiation eliminates a larger port ion of the genome than does 5 krad. This has been confirmed with isozyme analysis and chromosome counts which generally show the 5 krad asymmetric somatic hybrid plants to differ little from symmetric hybrids although they contain some significant exceptions. Isozyme data reveals the 10 and 20 krad plants to have received much less of the donor genome. Exact quantification is continuing using isozyme markers, chromosome counts and cDNA probes.