2000 and 2001, while ‘Rebecca’s Gold’ produced the smallest fruit (64 g) (2.3 oz). Fruit soluble solids range from 19 to 26.5% soluble solids in the varieties examined in both 2000 and 2001. Tree yield was greatest for the variety Prima 1216 in 2000 and for the varieties Prima 1216 and Prolific in 2001.

Vegetative propagation of pawpaw by conventional methods is difficult and micropropagation would be an alternative method for the production of many uniform plants of a selected superior genotype. Treatments were employed using various concentrations of sodium hypochlorite to disinfest explants to be used for callus induction. Quiescent buds and internodes were collected from 10-year-old trees of the varieties ‘Davis’, ‘Sunflower’, ‘Overleese’, ‘Prima 1216’, and ‘Prolific’ that were grown at the experimental farm of Domenico Montanari at Faenza, Italy. Explants were washed under tap water and then subjected to five disinfestation treatments consisting of immersion for 2 or 5 min in 1.0%, 2.0%, 2.5%, 3.5%, and 5.0% sodium hypochlorite. All treated explants were rinsed two times with sterile distilled water and then placed in petri dishes containing 10 mL (0.34 fl oz) of MS basal medium (Murashige and Skoog, 1962) supplemented with 2% sucrose and enriched with zeatine (5 μM), only in the case of internodes. Two different solidification agents were used with or without 0.3% activated charcoal, 0.7% Difco-Bacto agar (Sigma-Aldrich Chemie GmbH, Munich, Germany), and 0.3% Gelgrow (ICN Biomedicals Inc., Irvine, Calif.). The pH of the medium was adjusted to 5.8 ± 0.1 with 0.1 N sodium hydroxide before autoclaving. Cultures were incubated at 25 °C (77.0 °F) under a photoperiod of 16 h light (cool white fluorescent lamps, 35 μmol·m⁻²·s⁻¹) and 8 h dark. Cultures (15 explants per treatment) were subcultured every 20 d.

with or without 0.3% activated charcoal, 0.7% Difco-Bacto agar (Sigma-Aldrich Chemie GmbH, Munich, Germany), and 0.3% Gelgrow (ICN Biomedicals Inc., Irvine, Calif.). The pH of the medium was adjusted to 5.8 ± 0.1 with 0.1 N sodium hydroxide before autoclaving. Cultures were incubated at 25 circC (77.0 °F) under a photoperiod of 16 h light (cool white fluorescent lamps, 35 μ mol · m-2 · s-1) and 8 h dark. Cultures (15 explants per treatment) were subcultured every 20 d.

Most cultures were contaminated with fungal and bacterial organisms, which appeared on the medium surface within a few days. Explants that were free of microbial growth were found only with the buds of variety ‘Davis’ that were disinfested with 5% sodium hypochlorite for 2 min. Induction of callus on the ‘Davis’ explants began 15 d after being placed on the medium where Gelgrow had been added, but that contained no activated charcoal. Callus occurred directly at the cut surface of the explants. However, explants that produced callus exhibited browning and did not survive after the second subculture. The few cultures that had viable callus exhibited poor growth. Alternative surface disinfestation treatments with various chemical agents, concentrations and times, as well as alternative explants are currently being examined with the hope of increasing the number of aseptic explants.

In conclusion, over 3,000 pawpaw seedlings are under long-term evaluation for fruit appearance, production, quality, postharvest handling, as well as tree ornamental potential for Italy and the Mediterranean region. Evaluation of commercially available varieties has already identified selections that perform well in the region of Emilia Romagna (e.g., ‘sel. 938’, ‘sel. 1047’, and ‘sel. 1068’). Protocols for the propagation of pawpaw in vitro would offer many advantages for mass multiplication of desirable plants; however, the propagation of pawpaw in vitro has so far been met with limited success.

quality, postharvest handling, as well as tree ornamental potential for Italy and the Mediterranean region. Evaluation of commercially available varieties has already identified selections that perform well in the region of Emilia Romagna (e.g., ‘sel. 938’, ‘sel. 1047’, and ‘sel. 1068’). Protocols for the propagation of pawpaw in vitro would offer many advantages for mass multiplication of desirable plants; however, the propagation of pawpaw in vitro has so far been met with limited success.

Bellini, E. and D. Montanari. 1992a. La coltura dell'Asimina triloba annonacea per i climi temperati. L'Informatore Agrario 38:59–72.

Bellini, E. and D. Montanari. 1992b. La coltura dell'Asimina in Italia. Esperienze maturate a Faenza. L'Informatore Agrario 45:51–64.

Bellini, E. and D. Montanari. 2000. Asimina triloba, una realtà per la frutticoltura amatoriale italiana. Frutticoltura 1:54–61.

Layne, D.R. 1996. The pawpaw [Asimina triloba (L.) Dunal.]: A new fruit crop for Kentucky and the United States. HortScience 31:777–784.

McLaughlin, J.L. 1997. Anticancer and pesticidal components of pawpaw (Asimina triloba). Annu. Rpt. N. Nut Growers Assn. 88:97–106.

Murashige, T. and F. Skoog. 1962. A revised medium for rapid growth and bioassay with tobacco tissue cultures. Physiol. Plant. 51:473–497.

Peterson, R.N., J.P. Cherry, and J.G. Simmons. 1982. Composition of pawpaw (Asimina triloba) fruit. Annu. Rpt. N. Nut Growers Assn. 73:97–106.

Peterson, R.N. 1991 Pawpaw (Asimina). Acta Hort. 290:567–600.

Pomper, K.W., D.R. Layne, and R.N. Peterson. 1999. The pawpaw regional variety trial, p. 353–357. In: J. Janick (ed.). Perspectives on new crops and new uses. ASHS Press, Alex., Va.