From the Archives
of the Rare Fruit Council of Australia
by B. J. Watson, A. P. George, R. J. Nissen and B. I. Brown
Fruit Set in Carambola
Scientific name: Averrhoa carambola
Family: Oxalidaceae
(A note from the Editor, David Hodge)
Further
to a short article that appeared in the Port Curtis Branch February
1992 Newsletter, as quoted from an Ingham Branch Newsletter of August
1988. This mentions the problems of pollination and fruit set in
Carambola. The flowers are heterostylous, meaning the varieties have
styles of different lengths e.g.:
Style
length in the flower can be easily identified with a 10x hand lens The
following extract from "Carambola: a star on the horizon" by B.J.
Watson, A.P. George, R.J. Nissen and B.I. Brown in the January-February
1988 Queensland Agricultural Journal explains the significance of style
length.
Flowering and Fruit Development
The
carambola flower has usually five stamens, partially united at the base
and a five-lobed compound pistil. The style, which supports the
stigmas, is in two forms, short and long. Pollination studies in
Florida indicate that short-style (the stigmas located below the
stamens) cultivars are generally self-incompatible and require
pollination from long-style (stigmas above the stamens) types.
Long-style types are self-fertile.
The implications are not to plant short-style cultivars on their own.
However,
singly planted short-style cultivars have been known to bear heavily in
Queensland. Fruit are sometimes distorted in Fwang Tung cultivar. This
may be due to incomplete pollination or the effect of temperature on
pollen tube development. Style characteristics for some cultivars grown
in Queensland are presented in Table 1.
Generally only 0.5% of
the total flowers on one carambola tree must be pollinated to produce a
satisfactory crop. Unlike many fruits, achieving high yields is not a
problem with carambola, and in fact, overbearing is common and can lead
to limb breakage. Sweetness and fruit size may be increased by thinning
when fruit reach 20 to 50 mm in length.
The period from anthesis to fruit maturity varies according to temperature.
In
southern Queensland, there are two major flowering periods,
December-February and April-May. With the summer flowering, fruit
development takes 10 to 12 weeks from anthesis, while with autumn
flowering, it may take 12 to 16 weeks. The highest yields and best
quality fruit are produced from flowers set in the first flowering
period. Fruit maturing in late winter are generally small and not as
sweet.
In north Queensland, major flowerings occur in
September-November and February-April, although the peaks may vary by
up to 5 weeks from year to year. The period from anthesis to maturity
is about 12 weeks for both crops. However, individual trees may flower
over a long period, (up to 2 months in late summer) and consequently,
harvest may also be prolonged. The cycles tend to be 3 to 4 months
cropping and 2 to 4 months resting. The most notable production gap is
September to December (Figure 1). In comparison, Darwin in the Northern
Territory has major flowerings in January-february, April July and a
smaller one in September-October. Peak production is in April-May and
July-October, with a smaller peak in December-January (Figure 1).
Australia-wide,
the main production gaps are February-March and October-November. It is
not yet determined if trees can be manipulated to produce in these
periods. Some cultivars do have a wider spread of cropping (for
example, B4, B10, Hart and Maha) but none produces over 12 months.
Table 1. Style characteristics of some carambola cultivars grown in Queensland
| Short-style | Long-style | | B2 | B1 | | B8 | B6 | | B10 | B11 | | Fwang Tung | B16 | | Lu Tho | Star King | | Wheeler | Maha | | Kembangan | Arkin | | Pat Chun | 11-1 (Kary) | | 9-4 | | | 8-1 | (Kara) |
Figure 1. The peak production periods of carambola for different regions of Australia.
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