adventitious rooting in pawpaw. Pawpaw is a naturally suckering species, readily forming adventitious shoots from roots (Pomper and Layne, 2004). Propagation by root cuttings shows the most promise, with 56% of root cuttings greater than 5 cm in diameter producing shoots (Finneseth, 1997). However, clonal propagation by root cuttings requires the genotype to be on its own roots. Pawpaw cultivars are not currently self-rooted, but are budded or grafted onto a seedling rootstock (Pomper and Layne, 2004).

Studies utilizing many different methods of propagation have shown the effect of juvenility on adventitious rooting in pawpaw and other species. Odilo and Rafael (1976) found that only juvenile Annona cherimola cuttings produced roots, with 25% rooting at 5,000 ppm IBA. Stem cuttings from mature sources of pawpaw fail to root, whereas stem cuttings from more juvenile seedlings root more readily (Finneseth, 1997; Geneve, unpublished data) Finneseth (1997) found that stem cuttings taken from 7-month-old seedlings rooted at up to 16% whereas only one out of 5100 mature stem cuttings rooted. In preliminary studies at the University of Kentucky, stem cuttings from 2-month-old pawpaw seedlings rooted at up to 74%, while virtually no cuttings taken from older seedling sources (4-7 months) produced roots (R. Geneve, unpublished data).

Layering is a form of clonal plant propagation in which the shoot of a plant is induced to form roots while still attached to its mother plant. Various modifications of layering systems are often used to propagate more difficult-to-root species (Hartmann et al., 1997). Layering can enhance rooting by causing etiolation of the shoots as they grow through the medium placed on top of the mother plants. Etiolation enhances rooting by causing physiological changes in the plant (Hartmann et al., 1997). Several studies of various fruit and nut crops have shown the positive effect etiolation has on adventitious rooting, including apple (Delargy and Wright, 1978) and chestnut (Biricolti et al., 1994).

Trench layering is a modification of layering that is not often used in the commercial horticultural industry. To perform trench layering, the mother plants are planted and bent over so that they are in a horizontal position, and then are covered with soil, sawdust, or some other type of rooting medium. While trench layering is fairly uncommon, it has been used in extremely difficult-to-root plants, and has the advantage of a larger number of buds left to emerge as it is laid horizontally, and therefore this has the potential for a larger number of shoots to form plants in a small area. Trench layering