TOUGH NUTS TO CRACK: ADVANCES IN MICROPROPAGATION OF WOODY SPECIES

Abstract

Micropropagation of woody species has proved to be more challenging and difficult than micropropagation of numerous herbaceous species. Castanea spp. and Corylus spp. hybrids have been developed by plant breeders for the purpose of establishment of agroforestry plantations in the Midwestern states of the USA. Many of these hybrids have been developed by The American Chestnut Foundation (TACF), Meadowview, VA and by P.A. Rutter, Badgersett Research Farm, Canton, MN. Difficulties in conventional vegetative propagation approaches (cuttings, grafting) and the heterozygosity of seed populations have led researchers to employ micropropagation to obtain sufficient numbers of clonal plants for establishment of field plantations of such crops. We have utilized a forcing solution containing an anti-microbial chemical (8-hydroxyquinoline citrate, 8-HQC) and sucrose as a technique to obtain softwood outgrowth from cut woody stems that can be used as explant material for micropropagation. Inclusion of gibberellic acid in the forcing solution facilitated breaking bud dormancy of woody species in early to mid-winter, thus making it possible to obtain explants in the off-season for use in micropropagation research. Rooting difficulties have been overcome by use of a bilayer culture of activated charcoal-containing gelled medium overlaying a rooting medium from which light has been excluded. For Corylus, we have determined that a medium based in part on kernel constituents of the nut and higher than normal copper and myo-inositol significantly enhanced shoot proliferation and enabled production of several hundred 75 to 100 cm plants suitable for transplantation to the field.