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Callaway, M.B. 1993. Pawpaw (Asimina triloba): A "tropical" fruit for temperate climates. p. 505-515. In: J. Janick and J.E. Simon (eds.), New crops. Wiley, New York.

Pawpaw (Asimina triloba): A "Tropical" Fruit for Temperate Climates

M. Brett Callaway*


  1. DISTRIBUTION
  2. HORTICULTURE
    1. Culture
    2. Seed Propagation
    3. Vegetative Propagation
    4. Fruit Description, Composition, and Processing
    5. Cultivars
    6. Pests
    7. Research Needs
  3. REFERENCES
  4. Table 1
  5. Table 2
  6. Table 3
  7. Fig. 1
  8. Fig. 2

The pawpaw [Asimina triloba (L.) Dunal] is the largest fruit native to the United States (Darrow 1975). The genus Asimina is the only temperate climate representative of the tropical family Annonaceae. This family is famous for a number of fine fruit, including cherimoya (Annona cherimola Mill.), sugar apple (Annona squamosa L.), atemoya (Annona squamosa x A. cherimola), soursop (Annona muricata L.), custard apple (Annona reticulata L.), ilama (Annona diversifolia Safford), soncoya (Annona purpurea Moc. & Sesse), and biriba (Rollinia mucosa Baill.) (Morton, 1987). Of the nine species of Asimina found in the United States, A. triloba has the greatest potential for commercial fruit production. Other species are lacking in quality, size, hardiness, or other important characteristics. In addition to its promising potential for fruit production, certain parts of A. triloba plants contain asimicin, a compound with active pesticidal and neoplastic properties (Rupprecht et al. 1986, 1990; Ratnayake et al. 1993).

DISTRIBUTION

Fourteen species in the Annonaceae are native to the United States. These include nine species of Asimina, two species of Deeringothamnus, and three species of Annona. All Asimina species, excepting A. parviflora (Michx.) Dunal and A. triloba, are restricted to Florida and extreme southern portions of Georgia and Alabama (Callaway 1990). Asimina parviflora is distributed throughout the southeastern United States (Callaway 1990), while A. triloba is distributed over most of the eastern United States (Fig. 1) and even into extreme southern Canada. Deeringothamnus rugelii (B.L. Robbins) Small and D. pulchellus Small are rare plants native only to Florida (Kral 1983). The Annonas, A. glabra L., A. palustris L., and A. squamosa L., are found only in extreme southern Florida (Small 1913; Wunderlin 1982). I am aware of fruiting plantings of pawpaws on four continents (North America, Asia, Australia, and Europe).

HORTICULTURE

Culture

Since no scientific work has been done on cultural requirements of pawpaws, the following discussion on culture is based largely on my personal observations. I prefer planting seed into Rootrainer book containers (see propagation section below) then transplanting 10 to 20 cm seedlings into tall pots. Plants are left in the tall pots until they reach 0.5 to 1.0 m in height before transplanting. Seedlings should be started in pots for several reasons. First, pawpaw seedlings are reported to be sensitive to ultraviolet light (Peterson 1991). However, following a season of growth in partial shade, they no longer seem to be affected by direct sunlight. Rather, they grow and produce better in full sun (Wilson and Schemske 1980). Pots may be conveniently grouped under shadecloth for a season before transplanting to permanent field locations. Second, pawpaws have a reputation of being difficult to transplant and this difficulty increases with plant size. Yet, small plants are more difficult to maintain under field conditions. There is a tradeoff between transplanting success and maintenance of plants in the field. Plants grown in containers to approximately 1 m in height before transplanting largely circumvent these problems. Finally, plants may reach bearing size sooner when grown in containers before transplanting to the field, since optimal growing conditions are often more easily provided to container-grown plants.

Plants appear to need a "rest" period. Seedlings germinated in the greenhouse in December ceased growth in February and did not resume growth until June, even though suitable growing conditions were maintained during the entire period.

Pawpaws appear to benefit from mulching with leaves, compost, or other material high in organic matter. Since their native habitat is river floodplains, they may be somewhat more sensitive to low soil moisture than other fruit trees. Pawpaws seem to be sensitive to low humidities and dry winds.

Seed Propagation

Seed should be removed from the fruit, cleaned, and placed in a polyethylene bag with damp sphagnum moss and should not be allowed to dry out. Seed should be stratified at 2° to 4°C for 60 to 100 days before planting (Thomson 1982; USDA 1948). Seed should be planted about 2.5 cm deep. The depth of Rootrainer books, commonly used in the propagation of forest trees, is especially desirable because of pawpaw's long taproot. Once seedlings reach a height of 10 to 20 cm they can be transplanted into tall pots (10 x 10 x 36 cm) with partially open bottoms and placed on greenhouse benches. Taproots growing out the bottom of these pots are "air-pruned."

The rate and percentage of seed germination is stimulated by bottom heat (27°C) (Fig. 2) with most seedlings emerging between 45 and 90 days after planting. Acid scarification reduced percent germination. Evert and Payne (1991) reported increased percent germination with increased shading.

Vegetative Propagation

The most reliable and commonly used method of vegetative propagation is chip-budding. Root cuttings have been used successfully (USDA 1948), but softwood propagation methods (those using cuttings from soft, succulent, new growth) have not been satisfactorily developed. I was able to generate shoots in vitro from leaf explants using a modified a medium developed for tissue culture of Annona spp. (Nair et al. 1984a,b).

Fruit Description, Composition, and Processing

Fruit are produced in clusters and are oblong to banana-shaped, providing insight into the origin of one of A. triloba's early names, "Indiana banana." Fruit size ranges from quite small (20 g) to over 450 g. Skin is typically smooth and thin, ranging in color from green to bright yellow at maturity and turning brown or black after a frost. The fruit may be eaten when it becomes soft although some prefer to wait until after the skin has darkened. Flesh is custard-like in texture with flavor resembling cherimoya (Annona cherimola) or soursop (Annona muricata). Flesh color is typically orange but infrequently may be white (Callaway 1991). Large fruit usually have 10 to 15 large black seeds.

Peterson et al. (1982) evaluated the composition of pawpaw fruit (Table 1) and concluded that the fruit have a high nutritional quality compared to temperate fruits such as apple, peach, and grape. All commercially important fruit in the Annonaceae have relatively short shelf-lives. As Annonas are used in juices, ice cream, and other processed products similar processing may also be applicable to pawpaws.

Cultivars

A list of past and present cultivars has been compiled by Callaway (1990) and Peterson (1991). Many early cultivars have been lost over the years as the owners of nurseries and collections pass away. To date, there have been a total of 68 cultivars developed (Table 2). Only about 19 are commercially available (Table 3). Most are available in limited quantities from only one or two nurseries. The information available on these cultivars is based on the personal observations of very few persons; replicated yield tests have not been carried out. 'Overleese' and 'Sunflower' are probably the most widely grown cultivars and are generally considered to be among the highest quality. Relatively few nurseries sell pawpaw, although those who do, find it difficult to supply the demand.

Pests

Flyspeck (Zygophiala jamaicensis Mason) has been reported on fruit in Japan (Nasu and Kunoh 1987). A leaf spot caused by a complex of pathogens [Mycocentrospora asiminae (Ellis & Kellerm.) Deighton, Rhopaloconidium asiminae (Ellis & Morg.) Petr., and Phyllosticta asiminae Ellis & Kellerm.] has also been reported (Peterson 1991). None of these diseases caused significant damage to the fruit. Three lepidopterans have been reported to damage Asimina spp. Eurytides marcellus Cramer and Omphalocera munroei Martin feed on the leaves (Damman 1986). Talponia plummeriana Busck bores into the peduncle of flowers, causing serious loss of flowers in some years (Allard 1955). Fruit may also be eaten by wildlife including birds, foxes, opossums, squirrels, and raccoons.

Research Needs

Collection and testing of germplasm are needed. Since only 19 cultivars are available, wild germplasm remains an important source of genetic material for cultivar development and improvement. Superior selections from the wild should continue to be propagated and sold by nurserymen for home and commercial plantings. There is a great need for testing superior genotypes (wild selections, breeding lines, and cultivars) throughout the potential growing region to provide sound recommendations for growers.

Basic information is needed on the inheritance of commercially important traits, such as flowering behavior, fruit size, productivity, and maturity. This information is critical for the development of efficient, effective genetic improvement programs.

Basic horticultural information on such cultural practices as irrigation, fertilization, and pest control practices is also lacking. Information on pollination biology is needed. Wilson and Schemske (1980) demonstrated that fruit production on wild trees was limited by inadequate pollination. Only 0.41% of flowers set fruit on naturally pollinated plants in the wild, while as many as 17% of hand-pollinated flowers set fruit. A better understanding of the agents and mechanisms responsible for pawpaw pollination is needed to ensure reliable fruit set.

REFERENCES


*I acknowledge the helpful comments of Neal Peterson and Joe Hickman. Financial support during manuscript preparation was provided by USDA/CSRS Agreement No. KYX-10-91-17P to Kentucky State University.
Table 1. Composition of raw, unpeeled pawpaw fruit based on the edible portion (Peterson et al. 1982; Peterson 1991, and pers. commun.).

Constituent Range
Proximates (g/100 g)
Ash 0.6-0.7
Carbohydrate 16.8-22.4
Fat 0.6-1.4
Fiber 1.4-3.5
Food energy (Kcal/100 g) 77-89
Protein 0.8-1.4
Water 69.5-77.0
Vitamins (mg/100 g)
A (IU/100 g) 66-1.5
C 7.6-20.9
Niacin 1.1-1.2
Riboflavin 0.09-0.09
Thiamin 0.01-0.01
Minerals (mg/100 g)
Calcium 53-76
Copper 0.4-0.6
Iron 6.8-7.2
Magnesium 109-120
Manganese 2.5-2.6
Phosphorus 43-53
Potassium 314-368
Sulfur 62-78
Zinc 0.9-0.9
Fatty Acids (% of total)
Linoleic 8.1-9.0
Linolenic 16.9-24.4
Oleic 23.3-38.0
Palmitic 18.6-24.4
Palmitoleic 5.8-10.2
Sugars (g/100 g)
Fructose 1.3-2.8
Glucose 1.8-4.0
Sucrose 6.0-13.3
Essential Amino Acids (g/100 g of protein)
Arginine 3.00-3.83
Histidine 1.55-2.19
Isoleucine 4.7-6.8
Leucine 5.8-8.2
Lysine 4.2-6.3
Methionine 0.9-1.4
Phenylalanine 3.7-4.9
Threonine 3.2-4.6
Tryptophan 0.4-0.9
Valine 4.2-6.0


Table 2. Descriptions of pawpaw cultivars.

Name Description Place of origin Pedigree Reference
Arkansas Beauty   AR Selected from wild Anon. 1917; Pape 1965
Betty Wirt Fruit weighs up to 454 g, but averages 160 g Wirt County, WV Selected from wild Bartholomew 1962; Pape 1965
Buckman White flesh color, mild flavor; late to very late maturity   Selected by B. Buckman Zimmerman 1938; Zimmerman 1941
Cheatwood   Gallia, OH Selected from wild by J. Cheatwood Anon. 1917
Cheely   Iuka, IL Selected from wild by J. Cheely Anon. 1917
Cox's Favorite     Selected from wild Anon. 1917
Davis* Fruit 115 g, up to 12 cm long; yellow-fleshed; ripens 1st week of October in MI; green skin; seed large; keeps well in cold storage Bellevue, MI Selected from wild by Corwin Davis around 1959 Brooks and Olmo 1972; Davis 1982; L. Davis pers. commun.
Dr. Potter Small fruit size; mild flavor; ships fairly well; late maturity; rich yellow flesh Julietta, IN Selected from wild by B.S. Potter Anon. 1917
Duck       Vines 1960
Early Best   IN Selected from wild by W.C. Stout Anon. 1917
Early Cluster     Selected from wild Anon. 1917
Early Gold     Selected from wild Zimmerman 1938
Endicott   Villa Ridge, IL Selected from wild by G. Endicott Anon. 1917
Fairchild Early maturity   Selected by David Fairchild from 'Ketter' seed Zimmerman 1938; Zimmerman 1941
Ford Amend* Slightly smaller and earlier than 'Sunflower'; matures late Sept. in OR; flesh orange; skin greenish-yellow Portland, OR Selected by Ford Amend around 1950 from a seedling of unknown parentage M. Dolan pers. commun.
G-2     Zimmerman seed Peterson 1991
Gable Late to very late maturity PA Selected from wild by J. Gable Zimmerman 1938; Zimmerman 1941
Glaser   Evansville, IN Selected by P. Glaser Thomson 1982
Hann   AR Selected from wild Anon. 1917
Hengst     Selected from wild Peterson 1991
Holtwood     Selected from wild by W. Hoopes Vines 1960
Hope's August Early maturity Paint, OH Selected from wild by A. Hope Anon. 1917; Zimmerman 1941
Hope's September   Paint, OH Selected from wild by A. Hope Anon. 1917
Jumbo Late to very late maturity     Zimmerman 1941
Kercheval       Pape 1965
Ketter Matures evenly; skin comparatively thick & tough; does not discolor markedly; flesh medium yellow; mild but rich flavor, neither insipid nor cloying; large yellow fruit; early maturity Ironton, OH Selected by Mrs. F. Ketter Anon. 1917; Zimmerman 1941
Kirsten*   Aliquippa, PA Tom Mansell seedling 'Taytoo' x 'Overleese' J.S. Akin pers. commun.
Kurle Small-medium in size; yellow flesh and skin MI Seedling by R. Kurle from 'Davis' Kurle 1982
Lawvere       Pape 1965
Little Rosie Small fruit size Evansville, IN Selected by R. Glaser Glaser 1982
Long John     Selected by B. Buckman Zimmerman 1938
M-1     Selected by J. McKay from 'G-2' seedling Peterson 1991
Mango*   Tifton, GA Selected by Major Collins J. Gordon pers. commun.; Peterson 1991
Martin Large fruit size (Zimmerman says small size); flesh yellow & of superior quality (Zimmerman says skin tough); withstands cold well Springfield, OH Selected from wild by S.C. Martin Anon. 1917; Zimmerman 1941
Mary Foos Johnson* Similar to 'Sunflower'; original located at the North Wilamette Expt. Sta., Auroe, OR   Seedling given to North Wilamette Expt. Sta. by Ms. Mary Foos Johnson Pape 1965
Mason /WLW*   Mason, OH Selected from wild by E.J. Downing Peterson 1991
Middletown   Middletown, OH Selected from wild by E.J. Downing Peterson 1991
Mitchell* Fruit medium-size; skin slightly yellow; flesh golden; flavor "superb" Jefferson Co., IL Selected from wild by Joe Hickman J. Hickman pers. commun.
Mudge     Selected from wild Pape 1965
NC-1* Fruit 340 g; few seed; yellow flesh and skin; thin skin; early, maturing Sept. 15 in Ontario Ontario, Canada Selected by R.D. Campbell around 1976 from 'Davis' x 'Overleese' R.D. Campbell pers. commun.; L. Davis pers. commun.
Osborne Late to very late maturity   Selected from wild Zimmerman 1938; Zimmerman 1941
Oswald   Hagerstown, MD Selected from wild by E. Oswald Anon. 1917
Overleese* Fruit 340 g; bears in clusters of 3 to 5; ripens 1st week of Oct. in MI Rushville, IN Selected from wild by W.B. Ward around 1950 Davis 1982; Davis 1986; Pape 1965; Peterson 1991
PA-Golden* Flesh golden; skin yellow; matures mid-Sept. in Amherst, NY Amherst, NY Seedling selected by John Gordon around 1982 from seed originating from George Slate collection. J. Gordon pers. commun.
Prolific* Fruit 200-225 g; yellow flesh; ripens 1st week of Oct. in MI Bellevue, MI Seedling from Corwin Davis orchard Davis 1986; L. Davis pers. commun.
Propst Early     Selected from wild Anon. 1917
Rebecca's Gold* Fruit kidney-shaped, 85-170 g; flesh yellow CA Selected by J.M. Riley in 1974 from Corwin Davis seed J.S. Akin pers. commun.; California Rare Fruit Growers 1982; M. Dolan pers. commun.; Peterson 1991
Rees Flesh pale yellow and of good flavor; not a large fruit size Pleasanton, KS Selected from wild by W. Rees Anon. 1917
Roach   Dekalb, MO Selected from wild by J.C. Roach Anon. 1917
SAA-Overleese* Fruit 285 g, rounded shape; flesh yellow; skin green; few seed; matures mid-Oct. in Amherst, NY Amherst, NY Seedling selected by John Gordon around 1982 from 'Overleese' seed. J. Gordon pers. commun.
SAA-Zimmerman* Fruit 170-225 g; few seed; yellow flesh and skin Amherst, NY Seedling selected by John Gordon around 1982 from seed originating from G.A. Zimmerman collection. J. Gordon pers. commun.
Schriber     Selected from wild Zimmerman 1938
Scott   WV Selected from wild by C.S. Scott Anon. 1917
Shannondale Late to very late maturity     Zimmerman 1938; Zimmerman 1941
Silver Creek Medium sized fruit Millstedt, IL or Silver Creek, NY   J. Gordon pers. commun.; Thomson 1982
Sunflower* Fruit up to 225 g; butter-color flesh; skin yellowish; few seed; ripens 1st week of Oct. in MI Chanute, KS Selected from wild by Milo Gibson around 1970 Davis 1979; Davis 1982; Davis 1983b; Davis 1986
Sweet Alice*   Mentor, OH Selected by Homer Jacobs of the Holden Arboretum in 1934 Peterson 1991; Thomson 1982
Talbot Fruit 285 g; flesh yellow; overall quality average Linton, IN Chance seedling selected about 1950 by John Talbot from Corwin Davis seed. R.D. Campbell pers. commun.
Taylor Not the same as 'Taylor' described below; flesh light color, mild flavor; late to very late maturity   Selected from wild Zimmerman 1938; Zimmerman 1941
Taylor* Small fruit; bears up to 7 fruit in a cluster; yellow flesh, green skin; ripens 1st week of Oct. in MI Eaton Rapids, MI Selected from wild by Corwin Davis in 1968 Davis 1969; Davis 1982; Davis 1983b; Davis 1986; L. Davis pers. commun.
Taytwo* Fruit up to 285 g; begins ripening 10th of Oct. in MI; skin light green when ripe; flesh yellow; sometimes spelled 'Taytoo' Eaton Rapids, MI Selected from wild by Corwin Davis in 1968 Davis 1969; Davis 1982; Davis 1983b; Davis 1986; L. Davis pers. commun.; Mansell 1986
Tiedke Late to very late maturity   Selected from wild Zimmerman 1938; Zimmerman 1941
Uncle Tom Probably the first named variety on record; ripens mid-Sept. in IN; fruit sets singly and in pairs Cartersburg, IN Selected from wild by J.A. Little around 1896 Little 1905
Van Der Bogart Very similar to PA-Golden; matures mid-Sept. in Ithaca, NY Ithaca, NY Selected by Francis Van Der Bogart around 1970 from seed originating from the G.A. Zimmerman collection. J. Gordon pers. commun.
Vena Possibly the same as 'Talbot' Linton, IN?   R.D. Campbell pers. commun.
Wells* Fruit 340-400 g; skin green; flesh orange Salem, IN Selected from wild by David Wells in 1990 Callaway 1991
Wilson* Fruit medium-size; skin yellow; flesh golden On Black Mountain in Harlan County KY Selected from wild by John Creech J. Hickman pers. commun.
Zimmerman     G.A. Zimmerman seed Peterson 1991
* These cultivars are commercially available.


Table 3. Suppliers of pawpaw cultivars.

J.S. Akin
Sherwood's Greenhouses
P.O. Box 6
Sibley, LA 71073
Phone: (318) 377-3653
Cultivars: Davis, Mango, Overleese, Rebecca's Gold, Sunflower, Sweet Alice, and Wilson
Send Self-Addressed Stamped Envelope for price list
Annie Black
Hidden Springs Nursery
Rt. 14, Box 159
Cookville, TN 38501
Phone (931) 268-9889
Cultivars: Sunflower and Taylor
Catalog $0.40
Corwin and Letha Davis
20865 Junction Road
Bellevue, MI 49021
Phone (616) 781-7402
Cultivars: Davis, Overleese, Prolific, Sunflower, Taylor, and Taytwo
Include Self-Addressed Stamped Envelope.
Michael Dolan
Burnt Ridge Nursery and Orchards
432 Burnt Ridge Rd.
Onalaska, WA 98570
Phone: (206) 985-2873
Cultivars: Sunflower and Ford Amend
Send Self-Addressed Stamped Envelope for free catalog
J.H. Gordon, Jr.
1385 Campbell Blvd.
Amherst, NY 14228-1404
Phone (716) 691-9371
Cultivars: PA-Golden, SAA-Overleese, and SAA-Zimmerman
Louisiana Nursery
Rt. 7, Box 43
Opelousas, LA 70570
Phone: (318) 948-3696
Cultivars: Mitchell, Overleese, and Wilson.
Catalog $5.00
Northwoods Nursery
28696 S. Cramer Rd.
Molalla, OR 97038
Phone (503) 651-3737
Cultivars: Mary Foos Johnson, Prolific, Rebecca's Gold, Sunflower, and Wells
Oregon Exotics Rare Fruit Nursery
Jerry Black
1065 Messinger Rd.
Grants Pass, OR 97527
Phone: (503) 846-7578
Cultivar: W.L.W. Mason
Robert Seip
Lennilea Farm Nursery
R.D. 1, Box 683
Alburtis, PA 18011
Phone (215) 845-2077
Cultivars: Mango, Sunflower, and Sweet Alice


Fig. 1. Distribution of Asimina triloba in the United States. Source: Alabama (Clark 1971); Arkansas (Smith 1978); Florida (Kral 1960); Georgia (Jones and Coile 1988); Illinois (Mohlenbrock 1981); Indiana (Deam 1940); Iowa (Pammel and King 1930; The Great Plains Flora Association 1977; Stephens 1969); Kansas (The Great Plains Flora Association 1977; Stephens, 1969); Kentucky (Callaway unpublished; Johnson and Nicely, 1990; Kral, 1960); Louisana (Kral 1960); Maryland (Kral 1960); Michigan (Billington 1949); Mississippi (Kral 1960); Missouri (Steyermark 1963); Nebraska (Petersen 1912; The Great Plains Flora Association 1977); New Jersey (Hough 1983); New York (Bowden and Miller 1951); North Carolina (Radford et al. 1968); Ohio (Braun 1961); Oklahoma (Little 1981; The Great Plains Flora Association 1977); Pennsylvania (Bowden and Miller 1951; Kral, 1960); South Carolina (Radford et al. 1968); Tennessee (Kral 1960); Texas (Kral 1960; Simpson 1988); Virginia (Harvill et al. 1977); and West Virginia (Kral 1960).

Fig. 2. Rate of germination over time as influenced by bottom heat (27°C) and acid scarification with 36N sulfuric acid.