Kirk W. Pomper,1 Desmond R. Layne,2 and Snake C. Jones3
ADDITIONAL INDEX WORDS. Asimina triloba, bottom heat, chlorophyll, root : shoot ratio, kentucky banana, fertilizer regime, shading, biomass, propagation
SUMMARY. Pawpaw (Asimina triloba) is a native North American tree that has potential as a new fruit crop or for use in landscapes, but until recently, little information has been available to nurseries on container-ized production of this species. Pawpaw seedlings develop a strong taproot with a fragile root system, which can be easily damaged upon digging; therefore, most nurseries propagate trees in containers. Pawpaw seed requires stratification for optimal germination and seed is sensitive to desiccation. The seed also cannot tolerate freezing temperatures [< -15 circ C (5.0 circ F)]. A well-aerated potting substrate with a high sphagnum peat moss component (>75% by volume), cation exchange capacity, and water holding capacity can be used effectively in container production. Tall containers should be used to accommodate the developing taproot of seedlings. The slow-release fertilizer Osmocote 14-14-14 (14N-6.1P-11.6K) incorporated into Pro-Mix BX potting substrate can be used effectively as the sole fertilizer source at a treatment rate of 2.22 kg·m-3 (3.742 lb/yard3) in containerized pawpaw production. It can also be used at a lower rate of 0.81 kg·m-3 (1.365 lb/yard3) when supplemented with weekly applications of 500 mg·L-1 (ppm) of Peters 20-20-20 (20N-8.78P-16.6K) liquid-feed fertilizer. Bottom heating [32 °C (89.6 °F)] of container-grown pawpaw seedlings results in greater lateral and total root dry weight than in seedlings grown at ambient temperature [24 °C (75.2 °F)], which could increase the rate of establishment of seedlings in the field. Bottom heating of container-grown pawpaw seedlings could decrease both the time to produce a saleable plant and the cost of heating greenhouses. Growth of containerized pawpaw seedlings is enhanced by low to moderate shading with polypropylene shade fabric (28% or 51%) outdoors and low shading (33%) in the greenhouse, in a manner typical of that reported for other shade-preferring plants. Low to moderate shading of pawpaw seedlings grown outdoors greatly increases leaf number, total leaf area, and total plant dry weight compared to nonshaded seedlings, suggesting that commercial nurseries can improve production of containerized pawpaw seedlings using a shading regime outdoors.
The pawpaw is a native North American tree fruit that has potential for use as a new high-value fruit crop or in landscapes (Layne, 1996; Pomper et al., 1999). Pawpaw fruit possess a unique, almost tropical flavor, resembling a blend of banana (Musa × paradisiaca), mango (Mangifera indica), and pineapple (Ananas comosus), and offer excellent fresh market and processing potential. Difficulties in nursery propagation have been a major factor limiting development of a commercial paw-paw fruit industry. Pawpaw seedlings develop a strong taproot with a fragile root system, which can be easily damaged upon digging (Layne, 1996); therefore, most nurseries propagate trees in containers (author, unpublished). This results in a significantly greater cost to the purchaser; however, these trees usually have strong, healthy root systems at transplanting. At Kentucky State University our long-term goal is to enhance container production of robust pawpaw seedlings that would be well-suited either for grafting or for transplanting to orchards or home landscapes.
This research was supported by U.S. Dept. of Agriculture, Cooperative State Research, Education, and Extension Service Agreement no. KYX-10-97-28P to Kentucky State University. The technical assistance of E. Reed is also gratefully acknowledged by the authors.
1Principal investigator of horticulture and curator, USDA National Clonal Germplasm Repository for Asimina species., Atwood Research Facility, Kentucky State University (KSU), Frankfort, KY 40601-2355. To whom reprint requests should be addressed.
2Associate professor of pomology and extension fruit specialist, Dept. of Horticulture, Box 340375, Clemson Univ., Clemson, SC 29634-0375.
3Research assistant, Horticulture Program, Kentucky State University.