J.W. Van Sambeek

Thidiazuron stimulates shoot organogenesis and somatic embryogenesis in white ash (Fraxinus americana L.)

Immature and mature nonstratified seeds of white ash (Fraxinus americana L.) were dissected transversely and 2/3 of each seed was placed onto agar-solidified Murashige and Skoog medium. Adventitious buds, shoots, and somatic embryos formed on callus, cotyledons, and hypocotyls of the resulting seedlings. Shoot organogenesis was induced on explants cultured on medium with 10 μM thidiazuron but not on explants on media with benzyladenine (BA) or isopentenyladenine. Not all seed sources were equally capable of shoot organogenesis and embryogenesis. Atypical of adventitious regeneration of other woody plants, mature seed explants of white ash were more organogenic with shoots that elongated better than explants from immature seeds. Somatic embryogenesis was observed in cultures where mature seeds were first cultured for 4 weeks on a medium containing 10 μM adenine 2,4-dichlorophenoxyacetic acid in combination with 0.1 and 1.0 μM thidiazuron, followed by transfer to a medium containing 0.05 μM 6-benzyladenine and 0.5 μM naphthaleneacetic acid. Adventitious shoots and epicotyls from both seedlings and germinated somatic embryos were rooted under intermittent mist and acclimatized to the greenhouse.

Hardwood silvopasture management in North America

Hardwood silvopasture management has great potential throughout the Central Hardwood Region in the United States, but has been little utilized due to the lack of available information on its application. However, more than one-third of farm woodlands within the region are being grazed without the benefit of the application of silvopasture principles. The University of Missouri Center for Agroforestry has undertaken a major research initiative to further develop and build upon the fragmented information that is available on hardwood silvopastoral management. Ten years of screening forage species (grasses and legumes) for shade tolerance has clearly demonstrated that many cool-season forages benefit from 40% to 60% shade when grown in Missouri – a finding that could likely be extrapolated to the entire region of the Midwestern United States. Grazing trials have proven to be successful in the short-term. Long-term research is currently underway to fully document the interactions between hardwood trees, cattle and forage.

Adventitious regeneration of Juglans nigra L. (eastern black walnut)

Somatic embryos and adventitious shoots were initiated from immature cotyledons 10–14 weeks after anthesis. Maximum embryogenesis occurred 12 weeks after anthesis and maximum shoot organogenesis occurred 14 weeks after anthesis. The best treatment for induction of somatic embryos and adventitious shoots from immature cotyledon explants was on agar-solidified WPM supplemented with 0.1 μM 2,4-D and 5.0 μM TDZ and incubated in light for the first four weeks. Rooting of adventitious shoots was best if they were quickdipped in 2.5 mM IBA and 1.25 mM NAA in 1% dimethyl formamide and 3.9% ethanol (1∶20 Woods Rooting Compound: water, by volume). Plantlets from rooted adventitious shoots were acclimatized to the greenhouse.

Variation among black walnut seedling families in resistance to competition and allelopathy

SummaryOf three environmental variables affecting black walnut seedling establishment, moisture stress overshadowed the effects of fescue leachate and fertilizer. Interactions between moisture stress and family and between fescue leachate and moisture stress for both seedling height and dry weight suggested that selection for tolerance to moisture stress is possible, whereas progress from selecting for resistance to fescue leachate would be difficult. Family response to high moisture stress resulted in reductions of 17 to 33 percent in height and 36 to 48 percent in dry weight when compared with seedlings grown under moist conditions. The only effect of fertilization was a 9 percent decrease in seedling survival under high moisture stress conditions.

Variation among four white ash families in response to competition and allelopathy

Analysis of three environmental variables affecting seedling growth of four half-sib white ash families was dominated by a three-way interaction between soil moisture stress, fescue leachate, and family. Of these, soil moisture stress contributed by far the most to the interaction and resulted in an average growth decline of 62%. Although fescue leachate appeared to be phytotoxic to ash seedlings, it had a lesser effect resulting in changes in height rankings among families. Seedling families which grew well under moisture stress also tended to be tallest in the presence of fescue leachate. However, seedling families which were tallest under optimum growing conditions were not necessarily tallest when exposed to moisture stress.