Somatic Embryogenesis and Plant Regeneration of Wiregrass (Aristida stricta) and Creeping Bluestem (Schizachyrium scoparium var. stoloniferum)

Initiation of callus and induction of embryogenesis were achieved from both wiregrass and creeping bluestem. MS basal medium containing coconut milk, sucrose, and 2,4-D were used to initiate callus from young inflorescence of wiregrass and creeping bluestem. The presence of 2,4-D was found to be essential for the induction and early development of embryoids, possibly up to the globular stage. In the case of bluestem, initiation of embryogenic callus required the presence of a low concentration of BA; using only 2,4-D resulted in more non-embryogenic callus. More globular embryos were formed when embryogenic cultures grew rapidly without subculturing, or after being transferred to a hormone-free or a reduced 2,4-D medium. Plant regeneration was carried on a hormone-free MS medium. Initiation of cell suspension and induction of embryoid formation of wiregrass were achieved. However, maintaining cell suspensions seems to have some problems. A majority of the cells were thick-walled, elongated, and non-dividing. No embryos were formed in suspension cultures planted onto solid media. Reinitiation of cell suspension culture of wiregrass is in progress. Initiation of creeping bluestem cell suspension culture was carried out in MS basal medium containing coconut milk, sucrose, and 2,4-D. The maintenance of the cell suspension cultures and induction of embryoid formation were tested under different combinations and concentrations of growth regulators. Suspension cultures were selected and planted onto semi-solid MS basal medium with or without growth regulators. Somatic embryoids formed from suspension culture 3 to 4 weeks after being planted on semi-solid medium. Germination and plant regeneration of somatic embryoid of creeping bluestem are in progress.

Cultural Conditions Affecting the Frequency of Embryoid Formation in Sweetpotato (Ipomoea batatas)

Somatic embryogenesis in sweetpotato is highly genotype dependent. Unfortunately, many desirable agronomic varieties do not produce embryos capable of germination when published protocols are followed. Using one responsive and three recalcitrant cultivars, we examined the effect on embryogenesis of auxin, nitrogen, and carbon; explant source; and desiccation. All cultivars formed proembryonic masses on medium supplemented with either 2,4-D or picloram; picloram favored the growth of nonembryogenic callus. Twenty mm each of ammonium and nitrate promoted the best proembryo formation in all cultivars. Ammonium was essential for embryogenesis; replacing ammonium with proline, glutamine, asparagine, glycine, or casein hydrolysate resulted in poor or no proembryo formation. More proembryos formed on medium supplemented with sucrose than with glucose, fructose, or maltose. Leaf discs from the first fully expanded leaf produced more embryos than younger leaves for all cultivars; discs taken from the lamina produced more embryos than discs including portions of the midrib. Proembryos matured and germinated only after at least 3 weeks on medium containing 5% w/v polyethylene glycol 8000, greater than 3.3 mm myo-inositol, and 1 or 10 μm abscisic acid. More whole plants were obtained from the responsive cultivar Jewel than from the recalcitrant genotypes.

Responsiveness to anther culture in cultivars and F1 crosses of spring wheat

Anther culturability of 43 cultivars and 6 F1 crosses representing different quality classes of spring wheat was studied using a glucose-containing, modified N6 medium (HNG). Generally high pollen embryoid formation (up to 111 embryoids per 100 anthers) was associated with lower green plant regeneration (up to 9.1 green plantlets per 100 embryoids) frequencies and a high proportion (63% on average) of albino plants. Anther response was found to be strongly affected by the genotype of the donor plants. Seven of the screened cultivars yielded more than one green regenerated plant per 100 anthers. The most responsive cultivars were Veery #2 (6.2), ST 6 (4.0), and Leader (3.6). No ability to regenerate green plantlets was shown by 10 of the genotypes. Anther responsiveness of F1 progenies as compared with the parental cultivars were different in each cross. Differences found between reciprocal crosses suggest that the cytoplasm of a donor plant may affect anther response. Haploid plants constituted 45% of the anther derived regenerants, while the remaining part was divided into 29% of spontaneous diploids and 26% of plants with abnormal chromosome numbers. Key words: Triticum aestivum, anther culture, doubled haploids, wheat