Journal of the NACAA
ISSN 2158-9429
Volume 9, Issue 1 - June, 2016

The Pawpaw: An Emerging Specialty Crop

Cantaluppi, C. J., Area Horticulture Agent, North Carolina Cooperative Extension Service

ABSTRACT

In an effort to look at specialty crops to bring in a higher income per acre to growers, the pawpaw provides an opportunity to bring a “lost” fruit into the public eye, largely due to the efforts of plant breeders who have “re-discovered” this delicious fruit with a flavor that is a cross between pineapple, mango, and banana that have selected for good flavor and large fruit size, making it a very desirable, high-value horticultural crop that is very attractive to consumers. A replicated cultivar trial of Pawpaw (Asimina triloba) was initiated to compare the yield and quality of the four cultivars and to make recommendations to growers.  The highest yielder in pounds of fruit per tree and pounds of fruit per acre was the Shenandoah cultivar in 2013.  The Susquehanna cultivar had the largest fruit weight in 2013 and 2015.  The Allegheny cultivar yielded the greatest number of fruits per tree as compared to other cultivars in 2013 and 2015.  

 


INTRODUCTION

Pawpaw (Asimina triloba) belongs to the Annonaceae, or the Custard Apple family, which include a large family of trees, shrubs, and lianas that are widespread throughout the Old and New World tropics.  Some of the finest fruits in the world belong to the tropical Annonaceae: namely cherimoya, guanabana (also called soursop), sweetsop, and custard apple.  The genus Asimina is indigenous to the temperate deciduous forests of eastern North America, and contains seven other species besides A. trilobaA. triloba is a wholly temperate climate species, the northernmost ranging and hardiest of the Asimina, which makes it unique among the Annonaceae.  It is indigenous to most of the northeastern states, excluding most of New York and the New England states. 

The pawpaw's range extends south to the Florida panhandle, west to eastern Texas and north, including eastern Oklahoma, Kansas, and southeast Nebraska and does not extend north of Missouri into Iowa except for the southeastern part, which borders along the Mississippi River and does not include the state of Wisconsin or north of the southern third of Michigan.  A. triloba is the largest edible native fruit of North America.  The other Asimina do not have fruit as large.  A. triloba is almost the last tree to leaf out in the spring, a trait reflecting its tropical origins.  Although the young leaves often appear chlorotic, this is only temporary.

In 1916, The American Genetics Association held a contest to exhibit the best pawaws.  The outcome of that meeting was to develop commercial varieties by "intelligent breeding" but unfortunately, it did not come to pass (9,10).  Between 1900 to 1950, pawpaw variety development included widespread selection from the wild and resulted in numerous varieties.  However, few breeders were active, and few varieties were developed through breeding.  Between 1950 and 1985, many varieties were selected from both wild and cultivated sources.  Increased breeding produced many varieties from open-pollinated crosses.  The preservation of germplasm from this period was not a problem since varieties were widely disseminated (5).

The last decades of the 20th century saw an increase of activity in pawpaw domestication.  In 1981, Neal Peterson began a large-scale breeding program to develop improved pawpaw varieties (4,5).  With the cooperation of the University of Maryland, he established evaluation orchards at their agricultural experiment stations at the Wye Research and Education Center, Queenstown, MD, and at Keedysville, MD.  All 1,483 accessions were open-pollinated seedlings, with most coming from the plant material that survived in the collections of four pawpaw breeders between 1985-2000.  Secondary germplasm came from other minor collections of the period, certain wild stands, and seven named varieties (5).

By 1994, Peterson had selected 18 advanced numbered selections and these were included with 10 named varieties in a set of regional variety trials conducted at 12 universities (7).  He identified three of his selections as superior: 'Shenandoah', 'Rappahannock', and 'Susquehanna' as of 2003 and as of 2015, he has named three others; 'Allegheny', 'Potomac', and 'Wabash'.(5)

In addition to the work of Peterson, a contest was conducted by Brett Callaway, Horticulturist at Kentucky State University, who patterned his contest on that of 1916 and meant to gather a wide geographic breadth of germplasm with which to initiate a breeding program.  His contest generated more than 400 entries from 14 states in 1990 (5).

The Callaway contest marked the beginning of a committed pawpaw research program at KSU, first headed by Callaway (1991-1993), then Desmond Layne (1993-1997), and currently Kirk Pomper (1998-Present).  A germplasm collection was started in 1991 with the seed collected through the contest.  In 1994, KSU was designated the official Asimina satellite repository of the USDA National Clonal Germplasm Repository, Corvallis, OR. (5)  As of 2003, when reported in HortScience, this contained over 1700 accessions, including 40 varieties, from 16 states (2,8).

Peterson's breeding project was the first pawpaw breeding and evaluation project involving thousands of seedlings, statistical measurements, and the use of selection indices.  His project demonstrates the results of one person working for 20 years with limited resources.  His design emphasized both quantity and quality, consisting of more than 1000 accessions using seedlings from the best germplasm available (5).

The task of pawpaw breeding is now in the hands of amateur scientists with little institutional backing; KSU is an exception.  The present pawpaw industry is too small to fund university breeding programs.  Thus, breeding is likely up to the amateur, who should join groups like the Northern Nut Growers Association, and the Paw Paw Foundation, and familiarize themselves with pawpaw history, biology, genetic resources, and pollination techniques (5).

Pawpaw breeding is long-term research, requiring roughly 10 years per generation and 6 years for testing.  However, neither extravagant budgets nor extensive acreage are required.  Two or three acres will suffice.  Persistence, a love of pawpaws, a logical mind, attention to detail, habits of close observation, and familiarity with the scientific method are required (5).

MATERIALS AND METHODS

Dormant, one-year-old trees, budded in the fall of 2006 at Peterson Pawpaws in Winchester, VA were hand dug at the nursery on April 23, 2007 and planted on a grower's farm, 12 miles north of Oxford, NC on April 24, 2007 in a Cecil clay loam soil.

The trial consisted of four different cultivars; Shenandoah, Susquehanna, Potomac, and Allegheny, that were bred and released by Mr. R. Neal Peterson, horticultural scientist and geneticist.  The characteristics of the cultivars are as follows:

SHENANDOAH

The Shenandoah tree has large fruit size, born in single-fruited clusters, with good yields.  It responds well to pruning. The flesh texture firmer than wild pawpaws, with a sweet mild flavor.  It originated as a seedling of 'Overleese' and is superior to its parent.  It has few seeds (6% by weight) (6).

SUSQUEHANNA

Susquehanna is outstanding for combining very large size (over one pound) with rich pawpaw flavor, great sweetness, exceptional fleshiness, and firm buttery texture, similar to avocado and a thickish skin.  It has moderate to good yields and responds well to pruning.  It also makes a beautiful ornamental tree in the home landscape.  Susquehanna originated as a seedling from the collection of the Blandy Experimental Farm.  It has the fewest seeds of any cultivar (3% by weight) (6).

POTOMAC

Potomac is extremely fleshy, with fruit size typically 12 ounces or more.  It has a sweet and rich flavor and a firm, melting, and smooth texture.  Flesh color is medium yellow.  The tree is medium in productivity with a strong apical dominance, and is very upright and less spreading than most.  The percent seed is about 4% by weight (6).

ALLEGHENY

Allegheny has a sweet and rich, with a hint of citrus.  Texture is medium firm and smooth with a yellow flesh color.  It is very productive, which causes fruit size to suffer, requiring fruit thinning to keep weight above 8 ounces.  Fruit contains more seeds than cultivars, with a percent seed of 8% by weight (6).  

The experimental design used was a randomized complete block.  Each of the four cultivars was replicated six times.  One tree equals one replication for a total of 24 trees.  The trees were spaced 10 feet between trees in the row and 15 feet between rows.  This would equal 290 trees per acre.  The orchard was maintained in permanent sod culture, which was mowed throughout the season.  Trees were irrigated with drip irrigation during the planting year, and only by natural rainfall in subsequent years.

 

Table 1.  Number of Fruit Per Tree.

Cultivar

Number of Fruit

Per Tree1 2013

Number of Fruit Per Tree1 2015

Allegheny

13a

18a

Shenandoah

8ab

 8a

Susquehanna

6ab

14a

Potomac

5b

14a

1Cultivars with the same letter within column are not statistically significant, Duncan’s Multiple Range Test, .05 level.

 

Table 2.  Average Weight of Fruit in lbs.

 

Cultivar

Average Weight of Fruit (lbs.)1 2013

Average Weight of Fruit (lbs.)1 2015

Susquehanna

0.58a

0.76a

Shenandoah

0.51a

0.47b

Potomac

0.41ab

0.64a

Allegheny

0.30b

0.34b

1Cultivars with the same letter within column are not statistically significant, Duncan’s Multiple Range Test .05 level.

 

Table 3.  Yield in Pounds of Fruit Per Tree.

 

Cultivar

Pounds of Fruit Per Tree1   2013             

Pounds of Fruit Per Tree 20151

Susquehanna

3.9a

5.9a

Allegheny

3.9a

5.7a

Shenandoah

4.1a

5.7a

Potomac

2.2a

8.9a

1Cultivars with the same letter within column are not statistically significant, Duncan’s Multiple Range Test, .05 level.

 

Table 4.  Yield in Pounds of Fruit Per Acre - 2013.

 

Cultivar

Pounds of Fruit /A 20131

Pounds of Fruit/A 20151

Susquehanna

1,139a

1,737a

Allegheny

1,124a

1,660a

Shenandoah

1,184a

1,651a

Potomac

639a

2,590a

1Cultivars with the same letter within column are not statistically significant, Duncan’s Multiple Range Test, .05 level.

 

RESULTS

The trees did not bear fruit until 2011, with about ten fruits being produced in the entire orchard, scattered among the cultivars.  No yield data was taken in 2011 because of the erratic production.   In 2012 and 2014, the blossoms were killed by frost.  The trees bore their first full crop in 2013, and produced a good crop in 2015.

There were eight harvest dates in 2013: August 26, 28, 29, and 30; and September 2, 4, 7, and 11.  All cultivars had ripe fruit throughout the total harvest period. 

In 2013, the Shenandoah cultivar yielded the greatest in lbs. of fruit per tree and lbs. of fruit per acre compared to the other cultivars (Tables 3 and 4).  The Allegheny cultivar yielded the greatest number of fruits per tree as compared to other cultivars in 2013 and 2015 (Table 1).

There were eight harvest dates in 2015: August 20, 21, 24, 25, 27, 30; and September 1 and 2. All cultivars had ripe fruit throughout the total harvest period.

In 2015, the Susquehanna cultivar produced the largest average fruit weight, as in 2013 (Table 2).  Yields in lbs. of fruit per tree and fruit per acre increased in 2015 as compared to 2013 among all cultivars (Tables 3 and 4).  The number of fruit per tree increased in 2015 as compared with 2013 for all cultivars (Table 1).  The average fruit weight of Susquehanna increased from ½ lb. in 2013 to ¾ lb. in 2015 (Table 2).  All other cultivars increased in fruit weight in 2015 as compared with 2013 with the exception of Shenandoah, which decreased slightly (Table 2).

In 2015, yield in lbs. of fruit per acre increased among all cultivars, with Potomac increasing four-fold (Table 4).

DISCUSSION

Fruit set in pawpaw is poor in nature because of various pollination issues.  However, it has been shown that with proper pollination under cultivated conditions, yields can be exceptional (1).  The flowers occur on one-year-old wood and are protogynous, meaning that the female stigmatic surface is receptive before the male pollen is mature.  Even if released on time, the pollen is often self-incompatible.  Thus, the flowers require cross-pollination from a different cultivar (1).

Means of pollination is also an issue, and natural pollinators are neither efficient nor dependable.  The reddish, meat colored flowers and their fetid, musky aroma are not attractive to bees but are attractive to beetles, carrion, and bottle flies.  Increases in pollination have been observed by the introduction of carrion to the orchard.  This, however, is an unusual orchard practice, and may be difficult for growers to adopt (1).

The pawpaw has been an under-utilized plant that has been recently re-introduced as a high-value horticultural crop that can fill a specialty market niche, greatly due to the plant breeding efforts of Mr. R. Neal Peterson.  His patented cultivars can weigh up to one pound per fruit.  Assuming a fruit yield of  1,000 lbs. per acre, a grower can make $1,500; selling 500-½lb. fruits at $3.00 each, and $2,500; selling 500-1lb. fruits at $5.00 each for a total of $4,000 per acre at retail markets. 

Grafted pawpaw trees of improved cultivars planted at the rate of 290 trees per acre, at  $25.00 per tree, would cost $7,250.00.  It would be safe to assume that it would take three good years of fruit production to pay for the trees and realize a profit, less any harvesting and marketing costs.  Being that improved pawpaw cultivars have just recently been introduced, the longevity of fruit production from these cultivars is not known at this time.

The pawpaw is well adapted to the Eastern U.S. climate and soil conditions.  It is hardy to the USDA growing zone 5 (-20 degrees F.) and needs at least 400 hours in annual chilling requirements (time exposed to 35-45 degrees F. during winter months.  This is a low chill requirement compared to other tree fruit species (apples 800 to 1,700 hours) and once met, the trees will begin to flower early in the spring.  A long, warm seaon is required to mature fruit; around 160 frost-free days (1).

The pawpaw is a unique/unusual fruit crop with high nutritional value and potential fro both fresh and processed market uses.  As a food source, pawpaw exceeds apple, peach and grape in vitamin, mineral, amino acid, and food energy values.  The current and primary market for fruit is as a fresh product in farmers markets and other direct sales outlets.  Though large-scale commercial processing markets do not yet exist, the fruit's intense flavor and aroma have significant potential in blended fruit drinks, baby food, ice cream, and as a substitute for banana in various baking recipes.  in Kentucky, various entrepreneurs are utilizing pawpaw as a local cuisine item for restaurants and in frozen custard and ice cream products (1).

REFERENCES

1.  Bratch, A.  (2009).  Specialty Crop Profile: Pawpaw.  Virginia Cooperative Extension, Publication 438-105.

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

3.  Peterson, R.N.  (1982).  A national pawpaw germplasm collection.  Pomona, N. Amer. Fruit Explorers Quart.  15:155-158.

4.  Peterson, R.N.  (1986).  Research on the pawpaw (Asimina triloba) at the University of Maryland.  N. Nut Growers Assn. Annu. Rpt.  77:73-78.

5.  Peterson, R.N.  (2003).  Pawpaw variety development: A history and future prospects.  HortTechnology 13 (3): 449-454.

6.  Peterson, R.N.  (2013).  Peterson Pawpaws.  www.petersonpawpaws.com.

7.  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.

8.  Pomper, K.W., S.B. Crabtree, S.P. Brown, S.C. Jones, T.M. Bonney, and D.R. Layne.  (2003).  Assessment of genetic diversity of pawpaw varieties with inter-simple sequence repeat markers.  J. Amer. Soc. Hort. Sci. 128(4): 521-525.

9.  Popenoe, W. (ed.).  (1916).  Where are the best papaws?  J. Hered. 7: 291-296.

10.  Popenoe, W. (ed.).  (1917).  The best papaws.  J. Hered. 8: 21-33.