Histology of Adventitious Root Formation and Phytohormone Analysis of American Chestnut Cuttings

Abstract The formation of adventitious roots (ARs) is a complex process. It plays an important role in the successful production of elite clones since it is a key step in the vegetative propagation of economically important horticultural woody species. The American chestnut (Castanea dentata) is a heritage species and is notoriously recalcitrant to stem rooting. As part of the efforts to understand American chestnut cuttings’ recalcitrance, we examined AR formation via histology and compared the phytohormone level profile between American chestnut and easy-to-root poplar cuttings (Populus x euramericana). It was found that ARs could be induced directly from American chestnut cuttings without callus formation. Adventitious roots of American chestnut were initiated from cambial derivatives and developed a vascular system connected with that of the stem. Compared to easy-to-root poplar, American chestnut cuttings had a low level of indole-3-acetic acid (IAA) and a high level of cytokinin (CK), abscisic acid (ABA), salicylic acid (SA), jasmonic acid (JA), and oxylipin 12-oxo-phytodienoic acid (OPDA). Hormone distribution between leaves and stems also differed between American chestnut and poplar. This unfavorite endogenous hormone profile may contribute to American chestnut cuttings’ recalcitrance to rooting. Species used in this study: American chestnut [Castanea dentata (Marsh.) Borkh.], poplar (Populus x euramericana). Chemicals used in this study: 1-Naphthaleneacetic acid (NAA).