From the Archives
of the Rare Fruit Council of Australia
by Roy Hart, NZTCA Research Co-ordinator
The Asimoya
Scientific name: Asimina triloba
Family: Annonaceae
Reprinted from: Quandong, 2nd Quarter 1996, Vol. 22 No. 1
Asimina triloba,
often called the American pawpaw, was a favourite food of the native
Indians and an essential part of the diet of the early European
settlers. It was harvested from wild patches and little cultivation of
this fruit has occurred since then.
A few commercial endeavours
and some variety selection have taken place, but this work has
generally been forgotten or lost as the enthusiasts have died and their
properties have been sold. Several enthusiasts championed them at the
beginning of the century, learning how to grow them and selecting
superior types. I know that at least 21 cultivars were named. However,
most of these, as far as I know, have been either lost or exist only in
private gardens.
Even in the natural state, many selections were
good enough for commercial production. But the fact that they were
originally so easy to obtain from the bush, meant few people bothered
to grow them themselves. Nevertheless, it is a crop we in New Zealand
should not discard without testing its worth.
Confused Naming
A
browse through American magazines is most frustrating. Their references
to pawpaws turn out to be not the pawpaw we know, that tropical
melon-shaped fruit, Carica papaya, belonging to the plant family Caricaceae. Instead, they mean a completely different fruit, the Asimina triloba.
This fruit was known to the Indians as 'Arsimin', and has also been
variously referred to as the Hardy Custard Apple and the Kentucky
Banana, which are equally confusing as names. The Asimina triloba actually belongs to the family Annonaceae, the same plant family which contains our cherimoya (Annona cherimola) and atemoya (Annona cherimola X A. squamosa).
Because of its close relationship with these other fruits, we are recommending the name 'Asimoya' as our new name for the Asimina triloba. It is a pleasant-sounding name, with the advantage that it avoids all confusion with the pawpaw, Carica papaya.
Some facts
Asimina triloba
is basically a diploid, 2n = 18, but some stands contain triploids.
Seedlings of these stands can be in the ratio of 40: 1. Triploids would
probably be seedless. If the crop developed, there would also be a
place for someone to produce tetraploids from the better types.
As
far as I know, there are none of the superior selections in New
Zealand. I don't even know that they still exist in the USA, but
hopefully some still do. Seed was introduced 10 or so years ago into
New Zealand and although only a few of the seedlings survived, some are
now beginning to fruit. Like the ones I visited recently in Hamilton.
Many, however, have grown slowly and haven't set fruit yet. I have
heard of none that have fruit worth writing home about.
Some General Information
The
tree, as seen in New Zealand, is very similar to a small cherimoya but
is reported to be much hardier in cold winter conditions. They often
sucker in the wild, so that a single plant may cover a large area
called a "patch" (as in the children's song "Way down yonder in the
Pawpaw Patch"). However, there were large specimen trees, with one
champion having a girth of 65cm, a height of 16 m and a spread of 18 m.
Growth,
from most reports, seems very slow for the first two seasons, unless
ideal conditions prevail. But there are two diverse schools of thought
about ideal conditions for young trees. One is that they need about 50
- 85% shade and the other is that they need really good sunlight. I
tend toward the idea that they need shade for at least two years.
Selected Superior Varieties in the USA
Little Rose (a pollinator), Davis, Kurle, Glaser, Sweet Alice, Vena, Rees, Over Eese, Uncle Tom.
Late Varieties: Gable, Tiedke, Jumbo, Shannondale, Osborne, Buckman, Martin, Taylor No.1 and No. 2.
Early Varieties: Fairchild (considered the best), Ketter(er) (2nd best), Hopes August.
Many
of these are names of early enthusiasts. If you discover any of these
make sure they are preserved, and I would love to hear about them.
Fruit
There
are two basic types of fruit white-fleshed and yellow-fleshed. The
white-fleshed type is generally considered late maturing, with a mild
to flat (even insipid) flavour.
The yellow-fleshed type
generally ripens earlier and has a rich flavour, some being too rich
but some delicious. These are the ones we want. The white one is also a
longer banana shape and the yellow a fatter oval.
Large fruit will weigh 250-340 grams, and are 8-13 cm long and 2-4 cm wide. Smaller fruit will weigh 86- 200 grams.
Skin
colour is green, turning brown to black when ripe. The flesh is green,
turning white or yellow (even pinkish) as they ripen. When the fruit is
ripe, the flesh goes buttery and the odour sweetens. They have a high
sugar content, 16% sucrose (similar to a banana) and 17% carbohydrate.
The flavour varies according to soil type and fertility.
The approximate fruit composition is: Flesh 50- 80%, Seeds 14-17%, Skin 6-10%.
Climate and Soil Types
In
the U.S.A. the asimoya (see how easily we slip into using the new name)
grow from Northern Florida to Ontario, and from Nebraska to Texas.
However, the main areas are Pennsylvania, Ohio and Indiana. It is
evident therefore, that there is a lot of plasticity in the asimoya
germplasm for adaption to various climates. The best types so far,
however, have come from Susquehanna, Potomac and Ohio.
The
general climate requirement is considered to be for winter chilling to
break bud dormancy, followed by a hot summer with between 150-260
growing days. A rainfall of 75cm in the growing season, or
supplementary irrigation, is needed. Soil can be from clay to sandy
loam but soils rich in humus are needed for regular good fruit
production - lots of mulch, decayed vegetable matter, along with
plentiful lime and potash.
Cropping
Good
cropping will initially need hand-pollination. This seems evident from
the number of trees in New Zealand that are flowering but not fruiting.
Current information is unclear whether all varieties are self fertile,
or whether they need crossing. A little trial and error should sort
that out. Given the variability in other characteristics, there are
probably both types.
Hand-pollination is very easy. Petals can be
removed to make it easier. The main difficulty is getting fresh pollen
when the female stigmas are receptive. Also, a gentle touch is needed,
as the style breaks easily. So use a light touch with a soft camel hair
brush. Well -grown trees should begin cropping after five years. Yields
of 50-100 fruit per tree are possible. As local trees so far are
setting 10 or less fruit per tree, we have a long way to go.
Harvesting
The
harvesting season in New Zealand will probably be between February and
May. This will depend on whether we have early or late types. Pick
fruit as they start to soften. The colour may also change. Store in a
cool place. The old method was to store them wrapped in oat straw. Most
fruit kept in a fridge should be ready to eat in two weeks. Longer
storing types may take longer.
Propagation
Ideally
seed should be kept damp in sphagnum or something similar. Cold
treatment in a fridge for 8 weeks and then soaking in water for 24
hours before sowing works well. Cover seed with at least 2 cm of soil.
Sowing can be direct into the field with 5 to 6 seeds per hill.
Cuttings
take relatively easily from softwood to semi-softwood. The size of the
cutting can vary considerably from 1 cm to 30 cm long. Where possible,
use bottom heat and mist. Less sophisticated methods will also work
reasonably well.
Grafting is best done from October to early November.
Transplanting into the Field
Asimoyas
are tricky things to transplant. Many are lost at this stage. The best
time to do this is probably between August and September. Shading and
irrigation will be worth trying, to minimise losses at this stage.
Conclusion
In New Zealand attempts to grow asimoya
have so far been slow and not very productive. This may be, to a large
extent, due to our lack of knowledge of what we are doing, plus the
fact we are growing seedlings rather than superior selection. I feel
sure we haven't seen the true potential of this crop yet.
What
we need to do is locate and import varieties such as Fairchild and
Ketter(er). Then learn how and where to grow them best. With our
wonderful climate we tend to expect everything to be easy. With a
little more effort we may see the asimoya's full potential.
This
article has been based on my own observations, plus reference material
from U.S.A. especially the Californian Rare Fruit Growers Handbook:
Pawpaw Tree - Asimina triloba, Volume 6 (1974).
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