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Rural Industries Research & Development Corporation
Summary of full report
Kabocha and Japanese
Pumpkin in Australia
by Dr Wendy Morgan and Professor David Midmore
August 2003
RIRDC Publication No 02/167 RIRDC Project No UCQ-10A
Japanese Pumpkin (Cucurbita moschata) and Kabocha (Cucurbita maxima) are members of the cucurbit or pumpkin family. In Japan, kabocha is known as nutty flavoured pumpkin (in Japanese - Kuri Kabocha) and commands quite high prices. Fruits are small (1.5-2.0 kg). New hybrids of the two species have smaller fruit, due to the higher fruit set rate. Kabocha is grown in Australia, for the domestic market and as a fresh (from Tasmania) and processed (from mainland Australia) product exported to Japan. Australia is, however, an insignificant supplier of the approximately 130,000 t imported annually to Japan.
A project, funded in part by RIRDC, allowed compilation of earlier data, and establishment of field trials from 1998-2001 in most states of Australia to identify national production capability, and to establish information sought by supply chain managers.
With yields ranging from 16-53 t/ha, kabocha can be grown in all states of Australia. The interspecific hybrids (C. moschata x C. maxima) tended to be the highest yielding varieties, due to their greater fruit set. Where fruit set was high (eg at Katherine, NT) two harvests could help to maximise yield per unit land area. It may be that the higher temperature range promoted more fruit set there than at other sites.
Fruit maturity (time from fruit set to harvest) was also longer at Katherine and Gatton (Qld) where diurnal temperature ranges were greater that at Tatura (Vic) and Mareeba (Qld).
Harvest protocol established in the trials comprised only one harvest, and this may have led to yields less than potential if smaller later-set fruit were not harvested.
Across all trials, the new variety Tetsukabuto out-yielded the traditional Delica and Pacifica, encouraging adoption of this variety for the domestic market. This variety needs either C. maxima or C. moschata planted nearby for pollination.
When evaluating the effect of site on growth and yields, the Northern Rivers region of NSW was considered unsuitable, due to disease (downy and powdery mildew) most likely induced by high humidity. Likewise, plantings that resulted in harvest beyond January in SE and Central Queensland invited sunburn. Winter plantings in the NT and summer plantings in NSW (Gosford) and Victoria (Tatura) resulted in highly acceptable yields, as did the sowings in Queensland (Mareeba).
As with yield, significant difference between varieties within site, and between sites, for quality measurements were recorded. The varieties often fell into three separate groups; the older varieties Delica, Pacifica; the interspecific hybrids Tetsukabuto (late Potkin); and the Australian varieties Ken's Special. While diameter, height, and therefore shape, was constant for most varieties across sites, this was not so for Tetsukabuto reinforcing the impression that fruit of this variety was not always mature at harvest. Tetsukabuto had also darker rind colour, and fewer skin warts/blemishes, and more total carotene levels than did Delica. Fruit visual characteristics were relatively insensitive to growing location, but the ratio of sucrose, glucose and fructose in the flesh varied between varieties, trials and sites. There is some evidence to support the conclusion that sucrose:glucose ratio increases with fruit maturity, and that fruit age may be a useful tool upon which to base harvest decisions. More research is required under controlled conditions to verify this.
As fresh fruit is exported from Tasmania to Japan, efforts were undertaken to reduce the extent of post-harvest rot (Fusarium colmorum) during storage. Older fruits appear to be more susceptible to rots, and this could influence the optimum time for harvest. While heat shock treatment (2, 8 or 16 hours at 36 or 38 C) was ineffective in reducing extent of rot, cold treatment (7 C for 28 days) was more useful. The use of acetic acid was effective at 50 l/l airspace in reducing spore germination and fungal rot, but it was phytotoxic to the fruit.
In summary, the trials
reported confirm that Australia can produce kabocha of acceptable quality
year round, if the variation in locations and planting dates is optimised.
The newer interspecific variety, Tetsukabuto, offers greater returns to
growers. Its acceptance as a processed product for Japan requires verification.
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