Multiple shoots were induced on Valenciatype peanut (Arachis hypogaea L.) explants cultured in vitro on a nutrient medium supplemented with thidiazuron. Zygotic embryos excised from mature seeds were germinated on Murashige-Skoog nutrient medium, and the resulting plantlets (8 days-old) were used as a source of explants. When cultured on a nutrient medium with increasing levels of thidiazuron (0.5 to 30 mg/l), expiants from various parts of the peanut plant (except the root) produced multiple shoot primordia which subsequently developed into individual shoots. Hypocotyl and cotyledon explants produced shoots in higher numbers than other explants (20 shoots per hypocotyl explant at all thidiazuron concentrations and 15 shoots per cotyledon explant at 30 mg/l). Shoots rooted normally on a basal Murashige-Skoog medium containing charcoal and developed into healthy and fertile plants when planted in soil.

No abstract

No abstract

Studies were conducted to improve adventitious shoot regeneration in sweetpotato [Ipomoea batatas (L.) Lam.], specifically to extend the protocol to many genotypes and to elicit production of multiple shoots per explant. The use of a two-stage procedure where excised petioles were incubated on Murashige and Skoog (MS) (1962) medium with 2,4-D (0.2 mg·liter–1) for 3 days and transferred to a second medium containing MS salts with thidiazuron and 2iP (0.05 mg·liter–1 each) resulted in shoot regeneration from eight of 13 genotypes tested, including elite sweetpotato cultivars such as `Jewel' and `Rojoblanco'. PI 318846-3 was the most regenerable genotype, with up to 77% of explants producing one to three shoots per explant. The orientation of the petiole on the nutrient medium was critical; those placed vertically inverted developed multiple shoots. Wounding explants through epidermal peeling with normal horizontal orientation of the explants during incubation also resulted in multiple shoot production (about three shoots per explant). Interference with auxin transport due to explant inversion or wounding may have stimulated increased shoot induction. Chemical names used: 2,4 dichlorophenoxyacetic acid (2,4-D); N-phenyl-N′-1,2,3-thiadiazol-5-ylurea (thidiazuron); N6-(2-isopentenyl) adenine (2iP).

An efficient in vitro plant regeneration system characterized by rapid and continuous production of somatic embryos using leaf and petiole expiants has been developed in sweetpotato [Ipomoea batatas L. (Lam.)]. The optimal somatic embryogenic response was obtained in the genotype PI 318846-3 with a two-step protocol: (1) stage I-incubation of expiants in the dark for 2 weeks on Murashige Skoog (MS) medium containing 2,4-dichlorophenoxyacetic acid (2,4-D) (2.5 mg/l) and 6-benzylaminopurine (0.25 mg/l) and, (2) stage II-culture in the light on MS medium with abscisic acid (ABA) (2.5 mg/l). The addition of ABA was critical for enhanced production of somatic embryos. Secondary somatic embryos were produced from the primary embryos cultured on MS medium with 2,4-D at 0.2 mg/l. The somatic embryos were converted into normal plantlets when cultured on basal MS medium. Upon transfer to soil, plants grew well and appeared normal with no mortality. The system of somatic embryogenesis described here will facilitate tissue culture, germplasm conservation and gene transfer research of sweetpotato due to its rapidity (6 to 10 weeks), prolific plant production by direct embryogenesis, ease of secondary somatic embryo production and reproducibility.