Rhizome and fibre development in early harvest ginger (Zingiber officinale Rosc)

Sanewski, G. M. (Garth Michael) (2002). Rhizome and fibre development in early harvest ginger (Zingiber officinale Rosc) PhD Thesis, School of Land, Crop and Food Sciences, The University of Queensland.

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Author Sanewski, G. M. (Garth Michael)
Thesis Title Rhizome and fibre development in early harvest ginger (Zingiber officinale Rosc)
School, Centre or Institute School of Land, Crop and Food Sciences
Institution The University of Queensland
Publication date 2002
Thesis type PhD Thesis
Supervisor A/Prof Shu Fukai
Dr John R. Wilson
Total pages 201
Language eng
Subjects 07 Agricultural and Veterinary Sciences
Formatted abstract

The Australian ginger industry is based predominantly on the production of high quality early harvest ginger for the confectionary market. Harvest of ginger for this market is made when the rhizomes are young and tender. The processing factory requires early harvest ginger to be between 45 % and 35 % choice grade as expressed as a percentage of total rhizome fresh mass. The % choice grade rhizome is determined by the 'blunt knife' method whereby the rhizome sample is cut into 2 mm slices with a knife with a 1 mm thick blunt blade and separated into those slices with visible fibre and those without fibre. The portion without fibre is called 'choice grade'. Early harvest grade ginger is processed into syruped or crystallised ginger for the confectionary trade.

The timing of the early harvest is critical. If harvested too early, tonnage will be low. If harvested too late, the % choice grade will be reduced. The optimum time of early harvest varies from year to year and is thought to be determined by environmental and endogenous factors.

This series of studies were initiated to better understand the development of fibre in ginger rhizomes and how to maximise the yield of choice ginger. Studies included the effect of the environmental factors, water, temperature, photoperiod and solar radiation as well as time of planting. Basic studies on the histology of fibre development and historical trends in ginger maturity were also completed.

Decline in % choice grade rhizome, as measured commercially, was the result of a combination of the cessation of extension growth of rhizomes and the thickening of the walls of the mature fibre cells. A marked change in rhizome phenology occurred around early harvest with a change from growth by extension to growth by starch accumulation. Compressive resistance was a good indicator of increases in fibre cell wall thickness and fibre toughness.

A review of factory grading data collected over 21 yrs indicated a large variation in the time of commencement of early harvest between farms and years which suggested daylength had comparatively little effect on the decline of choice grade rhizome. Environmental factors, particularly temperature, and cultural factors which were likely to vary from farm to farm, were considered more likely to be influential. Generally growers who obtain good yields of early harvest ginger with a high % of choice grade ginger are considered by others in the industry to have an ideal growing environment and follow good crop production practices.

A comparison of different times of planting indicated a similar time of early harvest despite up to 4 wks difference in planting date. Thermal analysis of early shoot growth indicated a relatively high base temperature requirement (14°C) explaining the comparative lack of advantage from earlier planting in shoot emergence. Although shoot emergence and early rhizome development were reduced in earlier plantings, the third and fourth order rhizome segments were initiated slightly earlier producing a yield advantage. Planting in mid-August was better than the standard mid-September.

A study of the effect of daylength indicated that extended daylength improved plant growth and yield but did not affect progress to maturity as indicated by time of early harvest. A 17 % increase in rhizome yield was achieved by extending daylength to 16 h.

Studies on the effect of temperature on ginger growth and development indicated the optimum temperature regime for rhizome yield to be around 25/15°C. Temperatures slightly lower than the optimum (20/10°C) inhibited the production of new knobs but allowed the accumulation of starch into the rhizome thus resulting in an increased mass ratio of old:young rhizome and a slightly accelerated decline of % choice grade rhizome. Decline in % choice grade rhizome occurred even with the optimum temperature regime for rhizome growth. Temperature is therefore considered to influence the decline of % choice grade rhizome but only slightly. Differences in topography and aspect on different farms have the potential to produce the differences in temperature that could result in the 'between farm' differences seen in the decline of % choice grade rhizome.

A decline in % choice grade rhizome occurred even in the absence of flowering thus indicating that competition for assimilate between flowering stems and the rhizome does not cause the decline in % choice grade rhizome.

Studies of the effect of water deficit indicated that water deficit did not hasten the decline of % choice grade rhizome as commonly believed by growers. Severe water deficit was shown to halt or reverse the decline in % choice grade rhizome through the withdrawal of starch from the rhizome. Similarly, a severe reduction in assimilate production, induced by heavy shading, did not increase the rate of decline in % choice grade rhizome. Heavy shading tended to reduce the starch component of the rhizome more so than the fibre component. As with water deficit, a significant reduction in rhizome starch content had the potential to halt or reverse the decline in % choice grade rhizome although at the expense of yield.

Overall, temperature was considered the dominant influence on the development of choice grade rhizome. Ginger was shown to have a relatively high base temperature of 14°C. Plant maturity, including the decline in % choice grade rhizome appears associated mainly with the accumulation of thermal units above this base temperature. In addition, temperatures lower than the optimum of 25/15°C resulted in a slightly faster decline in % choice grade rhizome mainly through a reduction in rhizome extension but continued thickening of fibres.

Recommendations to growers include planting in mid August where possible for a slight yield advantage. Extended daylength was also shown to improve yield by up to 17 % and as such also represents a substantial yield increase. Further investigation of the economics of applying extended daylength is recommended. Neither of these approaches will however affect the decline in % choice grade fibre. Factors, which were shown to halt or reverse the decline in % choice grade rhizome, had a significant deleterious effect on yield and could not be recommended.

The production region centred near Yandina in south-east Queensland is close to ideal given the temperatures, although the climate around Bundaberg may also be ideal if good quality water was available for irrigation. Production further north, while gaining some advantages in longer days, would probably experience excessively high temperatures leading to a higher ratio of shoot:rhizome.

Considerable variation in crude fibre content exists within the Zingiber officinale gene pool and a further investigation of the fibre characteristics of some of the more promising lines is warranted.

Keyword Ginger -- Australia.
Ginger industry -- Australia.

Document type: Thesis
Collection: UQ Theses (RHD) - UQ staff and students only
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Created: Tue, 07 Dec 2010, 12:25:30 EST by Ning Jing on behalf of Social Sciences and Humanities Library Service