GENETIC-VARIATION IN ROOTING ABILITY OF LOBLOLLY-PINE CUTTINGS - EFFECTS OF AUXIN AND FAMILY ON ROOTING BY HYPOCOTYL CUTTINGS

After about 20 days, hypocotyl cuttings from 20-day-old loblolly pine (Pinus taeda L.) seedlings rooted easily in the presence of the auxin indole-3-butyric acid (IBA), with roots forming directly from xylem pa renchyma. In contrast, woody cuttings from 1-2-year-old hedged seedlin gs formed roots indirectly from callus tissue in 60-90 days, but IBA h ad little effect on rooting. Variation in rooting among hypocotyls fro m both half- and full-sib families was highly significant in response to IBA, and rooting did not occur within 20 days unless IBA was applie d. Hypocotyls from poor rooting families tended to produce fewer roots per cutting than hypocotyls from good rooting families. Rooting by wo ody cuttings and hypocotyl cuttings from the same nine full-sib famili es was weakly correlated, raising the possibility that at least some c ommon genetically controlled processes were affecting rooting by both types of cutting. The phytotropin N-1-naphthylphthalamic acid (NPA), s upplied at 1 mu M with 10 mu M IBA, significantly inhibited rooting by hypocotyl cuttings from both good and poor rooting families, but ther e was no significant family x treatment interaction. Family variation in rooting ability may be a function of the frequency of occurrence of auxin-responsive cells in the hypocotyls.