could also be utilized in grafted plants, as buds from the scion could be rooted, and emerging shoots would be more distant from any shoots emerging from the rootstock and thus easier to differentiate from root suckers, unlike mound layering. Suriyapanant (1990) compared air and trench layering in apple rootstocks and found that trench layering was a superior method for at least one rootstock. Both air layered and trench layered shoots were wounded and treated with 8000 ppm IBA. Trench layered shoots were bent and pegged to lay horizontally in a trench. Wounding and IBA application was then performed. About 77% of air layered shoots of the MM106 rootstock rooted, while 100% of trench layered MM106 shoots produced roots. However, no significant differences in treatments were found in the other two rootstocks.

Our long-term goal is to develop a clonal propagation method where pawpaw genotypes can be propagated on their own roots. The hypotheses of this study were that pawpaw seedlings will root in a trench layering system in the greenhouse, increasing concentrations of auxin applied to girdled shoots will enhance rooting, and that shoots of ontogenetically more juvenile pawpaw seedlings will have greater rooting potential than shoots of ontogenetically more mature seedlings. The objectives for this study were to examine the role of juvenile plays in rooting of pawpaw and determine if trench layering with wounding and auxin applied to shoots would promote rooting of shoots.

Plant Material. For all experiments, pawpaw seed was harvested in 2001 from open-pollinated half-sib trees at the Keedysville, Md. orchard at the Western Maryland Research and Education Center. Seed was stratified at 5 °C for 3 months and was sown to a 3 cm depth in moist Pro-Mix ‘BX’ potting substrate (Premier Horticulture, Inc. Red Hill, Pa.) in 15 cm deep flats (on February 7, March 14, and April 4, 2002; and December 16, 2002, March 10, 2003, and May 12, 2003). Seedlings were grown in a white-washed greenhouse under a 16-h photoperiod supplemented by high pressure sodium lights with temperatures set at 24/30°C. Photosynthetic photon flux was measured at canopy level on a clear sunny representative day at 150-350 μmol·m⁻²·s⁻¹ by using a LiCor LI-185B photometer with a quantum sensor (LiCor, Lincoln, Nebr.). Flats were fertilized with Peters 20-20-20 (20N-8.6P-16.6K) water soluble fertilizer with micronutrients at 500 ppm once a week. Seedlings emerged approximately 45 days after sowing.