P&PDL Picture of the Week for
September 23, 2013

It’s pawpaw pickin’ time!

Bruce Bordelon, Professor, Department of Horticulture and Landscape Architecture, Purdue University

Pawpaw is a not-so-common fruit native to Indiana and others states in the East and Midwest. In fact, it is one of the few “tree fruits” native to North America. The paw paw (Asimina triloba) is the most northerly adapted member of the custard apple family, Annonaceae, a family of tropical and subtropical fruits that includes custard apple, cherimoya, soursop, atemoya and others.  Pawpaw is commonly known as the poor man’s banana, Indiana banana, Kentucky banana, etc.

Pawpaws have been prized for over a century and the subject of songs and lore, and the topic of a number of festivals held about this time each year when the pawpaws are ripe and ready for picking.

But are they a new commercial crop? That’s what a group of researchers is trying to determine. The Pawpaw Foundation established a Regional Variety Trial in 1999 to test new selections against the old standard varieties. Fourteen standard varieties (some from Indiana such as Wells and Overleese) are being compared to a number of selections from a breeding program in Maryland. One of the Regional Variety Trial plantings is at Purdue’s Meigs Horticulture Research Farm near Lafayette, IN (picture 1). We also have a publication on growing pawpaw (Ref. 1).

In its native habitat, the pawpaw is an understory tree that has a very open canopy, sparse flowering and fruiting, and can usually be found in a grove (e.g. a pawpaw patch) as the plant suckers readily from the roots to create a “colony” of trees that are all one genotype. But in an orchard setting in full sun, the trees are quite compact, reaching a height of 15-20 feet, with dense, dark green foliage (Picture 2). Leaves are very large and attractive (Picture 3). Fruit production can be sporadic, but is considerably better than in the wild. The fruits can be borne singly or in clusters of three to five fruit (Picture 4). Mature fruit size can range from an egg to a large baking potato (Picture 5). Some fruits can weigh as much as a pound each (Picture 6). Fruit can be harvested from the tree as it softens or it may drop when they are mature, but freshly harvested fruit may need a few days to fully ripen (Picture 7). The fruit is soft at maturity and the flesh is yellow to orange and soft, but not juicy. Large seeds are scattered through the flesh (Picture 8a,b). The aroma is wonderful, floral and tropical. The flavor is a bit like banana, mango or other tropical fruit. Some people love the taste of pawpaws, while others are not so enthusiastic

Pawpaws have almost no pest problems. The only disease is occasional leaf spot (Picture 9).  The large leaves are susceptible to damage from high winds (Picture 10).

The pawpaw has its own USDA National Clonal Germplasm Repository at Kentucky State University (Ref. 2). Over 2,000 trees from 17 states are planted at the KSU farm. KSU’s full time pawpaw research program, the only one of its kind in the world, conducts research directed at improving propagation methods, developing orchard management recommendations, conducting the regional variety trial, understanding fruit ripening and storage techniques, and germplasm collection and characterization of genetic diversity.

There are some concerns about consuming pawpaw. Like many tropical fruit, a certain percentage of the population may be allergic. Just this week I received an inquiry from a Purdue staff member who had gotten sick after eating pawpaw bread. Nausea after consuming pawpaw is a fairly common occurrence. Pawpaw seeds and bark have been known for many years as a source of bioactive compounds and have been used in folk medicine. At one time the seeds were used to produce an emetic, a medicine to induce vomiting.

The seeds and bark are known to contain annonacin, a very potent acetogenin. It has recently been shown that pawpaw fruit also contain a high concentration of annonacin, which is toxic to cortical neurons. Crude fruit extract also induced neurotoxicity, highlighting the need for additional studies to determine the potential risks of neurodegeneration associated with chronic exposure to pawpaw products (3). Consumption of a tropical relative of pawpaw Annona muricata (soursop, graviola, guanabana) has been strongly associated as a causal agent in "atypical Parkinsonsism" (4). The causative agent, annonacin, is present in many of the Annonaceae. It is thought to be responsible for up to 70% of Parkinsonian conditions in Guadeloupe. Exposure is typically through traditional food and "natural" medicines (5,6).

So, when it comes to pawpaw, perhaps it is best to enjoy the fruit in moderation.

References:

  1. Growing Pawpaws Purdue Extension Bulletin HO-220 http://www.hort.purdue.edu/ext/ho-220.pdf

  2. Kentucky State University Pawpaw website:  http://www.pawpaw.kysu.edu/default.htm

  3. Potts, L.F., F.A. Luzzio, S.C. Smith, M. Hetman, P. Champy, I. Levitan (2012) Annonacin in Asimina triloba fruit: Implication for neurotoxicity. NeuroToxicology 33: 53-58

  4. Champy, Pierre; et al. (2005). "Quantification of acetogenins in Annona muricata linked to atypical parkinsonism in guadeloupe". Movement Disorders 20: 1629–1633.

  5. Lannuzel A, Höglinger GU, Champy P, Michel PP, Hirsch EC, Ruberg M. (2006). "Is atypical parkinsonism in the Caribbean caused by the consumption of Annonacae?". J Neural Transm Suppl. Journal of Neural Transmission. Supplementa 70: 153–157.

  6. Caparros-Lefebvre D, Elbaz A. (1999). "Possible relation of atypical parkinsonism in the French West Indies with consumption of tropical plants: a case-control study". Lancet 354: 281–286.

Click image to enlarge

Pawpaw trees

Picture 1

Pawpaw tree

Picture 2

Leaves on pawpaw tree

Picture 3

Pawpaw fruit

Picture 4

Pawpaw fruit on ground

Picture 5

Pawpaw fruit in hand

Picture 6

Pawpaw fruit on ground

Picture 7

Pawpaw fruit cut open

Picture 8A

Paw paw fruit cut open

Picture 8B

Leaf spot

Picture 9

Wind damage

Picture 10

 

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service