Abstract
The use of air layer protocols to propagate cycad plants was recently described, creating opportunities to improve the procedures and identify applications. Mature
Cycas edentata
de Laub. trees in an Angeles City, Philippine garden were used as source plants to address three questions in this regard. First, 4 months of root growth following removal of large air layer propagules indicated that most of the 261 ± 5 cm of root growth originated from the fresh wound at the base of the detached stem, and only 16% of the post-transplant root growth occurred at the air layer wound. Second, direct comparison of large stem cuttings vs. air layer propagules of the same size indicated root growth of cutting propagules was minimal compared with root growth of air layer propagules. Air layer propagules added 306 ± 7 cm of new root growth and stem cuttings added 25 ± 8 cm of new root growth at 5 months postexcision. Third, the influence of sucker size on adventitious root growth of air layers vs. detached cuttings indicated larger suckers were more successful. All the stem cuttings 2 cm in diameter died, and 50% of the cuttings 4 cm in diameter died. In contrast, all air-layered suckers formed roots to provide successful propagules regardless of size. Air layer root length increased linearly from 12 cm for the 2-cm suckers to 33 cm for the 8-cm suckers. Detached cutting root length increased quadratically from 0 cm for the 2-cm to 14 cm for the 8-cm suckers. These findings indicated the new wound that is created by excision of an air-layered cycad stem should be treated with care because it will become the primary source of postexcision root growth. Moreover, extremely small suckers that are too small to use for stem cuttings can be used for successful asexual propagation with the use of air layer protocols.