CSIRO PUBLISHING
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Australian Journal of Agricultural Research, 2006, 57, 1087–1095
Effects of high temperature on the growth and composition of sugarcane internodes G. D. BonnettA,C,D , M. L. HewittB,C , and D. GlassopA,C A CSIRO
Plant Industry, Queensland Bioscience Precinct, 306 Carmody Road, St Lucia, QLD 4067, Australia. B CSIRO Plant Industry, Davies Laboratory, PMB, PO Aitkenvale, QLd 4814, Australia. C Cooperative Research Centre for Sugar Industry Innovation through Biotechnology, Level 5, John Hines Building, University of Queensland, St Lucia, QLD 4072, Australia. D Corresponding author. Email:
[email protected]
Abstract. Sugarcane grown in the Ord River district of Western Australia has lower sucrose content than expected from earlier trials and experience in other irrigated districts. High temperatures have been hypothesised as a possible cause. The effects of high temperature (above 32◦ C) on growth and carbon partitioning were investigated. A temperature regime of (25–38◦ C) was compared with (23–33◦ C). In one experiment, 7-month-old plants of cvv. Q117 and Q158 were subjected to the treatments for 2 months. In another experiment, the plants were allowed to regrow (ratoon) for 6 months. In both experiments, the higher temperature resulted in more, shorter internodes and higher moisture content. Most internodes from plants in the higher temperature treatment had lower sucrose content than internodes from the lower temperature. On a dry mass basis the internodes from the plants in the higher temperature had proportionately more fibre and hexoses but lower sucrose. Combined with an increased number of nodes in a stem of similar or shorter length this would result in higher stalk fibre and lower sucrose content. The data provided evidence that sugarcane partitions less carbon to stored sucrose when grown under high compared with low temperatures. The two cultivars partitioned carbon between soluble (sugars) and insoluble (fibre) fractions to different degrees. These experiments also indicate that the current models describing leaf appearance and perhaps sugarcane growth at temperatures above 32◦ C, in general, need revision. Additional keywords: carbon partitioning, sucrose content, fibre, leaf initiation.
Introduction Sugarcane is grown over a wide range of latitudes in Australia from around 30◦ S in northern New South Wales to 16◦ 30 S in Queensland and 15◦ 30 S in Western Australia. Consequently, the crop experiences a wide range of temperatures from sub zero to >40◦ C. The rates of leaf appearance (Bonnett 1998), tiller appearance (Inman-Bamber 1994) and canopy development (Inman-Bamber 1994; Robertson et al. 1998) are all functions of thermal time. However, the different base temperatures for these processes mean that many of the biologically significant processes that contribute to final yield and sucrose content respond to temperature differently. In an analysis of industry data by Leslie and Byth (2000), the sucrose contents, as estimated by polarimetry and reported as pol% dry matter content, of cane grown in the Ord River district in Western Australia was 42.0% compared with 49.3% for the Burdekin River district in Queensland. The relatively lower sucrose content obtained compared with the Burdekin River district, another irrigation area, may be due to the high temperatures experienced in summer in © CSIRO 2006
the Ord River district (Leslie and Byth 2000); November average maximum temperature of 38.7◦ C compared with 31.9◦ C in the Burdekin (Bureau of Meteorology 1988). Previous studies have examined growth and accumulation of sucrose in the range of 18–34◦ C (Glasziou et al. 1965), or 14–26◦ C (Robertson et al. 1998), but these temperatures are below the highest regularly experienced by the Ord River district. For various integrated measures of growth such as sugar concentration or content per plant, temperatures of 27◦ C (Ebrahim et al. 1998b) or 30◦ C (Glasziou et al. 1965) have been described as the optimum. Ebrahim et al. (1998b) used temperatures of 15 and 45◦ C as sub- and supra-optimal temperatures in their study of growth and sugar storage and found sucrose concentration was lower at 45◦ C than at both 27 and 15◦ C. Nevertheless, sugarcane is grown commercially in Iran with some average monthly temperatures above 45◦ C but with no reported negative effect on growth (Sund and Clements 1974). Sucrose content is in part determined by the proportion of carbon partitioned towards each of the soluble (sugars) and 10.1071/AR06042
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Australian Journal of Agricultural Research
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insoluble (fibre) fractions. Results from experimentation with tropical pasture grasses indicated that dry matter digestibility decreased during the summer months in subtropical sites and was lower at tropical sites (Wilson et al. 1986). Partitioning between soluble and insoluble dry matter fractions influences digestibility and this varies with temperature regime (Wilson and Ford 1971). In both of these cases, however, plants did not experience average temperatures above 35◦ C. In an attempt to determine the effects of the high temperatures on the growth and composition of stem internodes, temperature regimes reflecting the environments experienced by the Ord River and Burdekin River districts were reproduced in a temperature-controlled facility. The study was performed under higher light levels than the study by Ebrahim et al. (1998b) and in temperature regimes that represent the diurnal pattern rather than constant temperatures (Ebrahim et al. 1998b) or square-wave day/night changes imposed by Glasziou et al. (1965).
Table 1. Temperature regimes for the 2 treatments used in Expts 1 and 2, based on hot and moderate sugarcane-growing districts
Materials and methods
Sampling stalks in Expt 1
Growth of plants prior to placement in the glasshouse
When the plants were moved into the glasshouse, 5 pots of each cultivar were harvested as described below to obtain initial sugar measurements. Sampling was initiated when stalks of Q158 in the hot compartment started to sprawl. To eliminate any diurnal effects, plants were harvested over successive days between 12.00 p.m. and 2.00 p.m. Q158 was harvested on 11–12 January 2001 and Q117 on 15–16 January 2001. To avoid bias, replicates (n = 6) were removed alternately from the 2 treatments. Stalks were removed from each pot at the soil surface and the 4 tallest (where more than 4 stalks were present) were processed as follows. The height to the last fully expanded leaf marked on 10 November 2000, the height to the last fully expanded leaf on the date of harvest, and the number of internodes above and below the last fully expanded leaf marked on 10 November were recorded. Internodes 6 and 12 (–6, –12) below the leaf marked on 10 November and internodes 2 and 4 above this leaf were removed. The length, mass, and diameter (in the middle) were measured for each of the internodes individually. Internodes from the same position and pot were pooled. A 3–5 mm slice from the middle of each internode was removed and 2 subsamples collected. One subsample was weighed and then dried at 60◦ C (to calculate the moisture content) and the second was placed in a plastic tube and frozen in liquid nitrogen then stored at −80◦ C until the sugars were extracted.
Single-eye setts of cvv. Q158 and Q117 were planted into sand on 26 May 1999. Germinated setts were transferred one to a 27-L pot filled with a mixture of sand, vermiculite, and peat (6:1.9:0.9 v/v). Five kg each of lime and single superphosphate were added to the mixture. Plants were grown outside at Townsville (19◦ 15 S, 146◦ 46 E), watered twice a day and fertilised monthly with liquid fertiliser (Wuxal, Schering Pty Ltd, NSW, Australia), granular, slow-release fertiliser (Osmocote, Scotts Australia Pty Ltd, NSW, Australia; 14:6.1:11.6 N:P:K, 50 g/pot) and iron chelate (Barmac Industries Pty Ltd, Qld, Australia; 13.2% iron as FeEDTA, 5 g/pot). The plants were ratooned 29 March–6 April 2000. Plants were in a block of 5 rows orientated N–S with the Q158 plants being at the southern end of the block. As the 2 outside rows of the plants were shorter, only plants from the inner 3 rows were transferred into the core plot of the experiments. Experiment 1. Effects of temperature on 7-month-old cane Plants were moved into a naturally lit, polycarbonate-clad, controlledenvironment facility on 10 November 2000 and placed on individual trolleys with 2 vertical supports to which the stems were tied loosely with string. For each cultivar there were 3 rows (1.5-m apart) with 8 pots with no space between them. Q158 was placed at the most westerly end of each compartment. The plants were randomly allocated to treatments. The middle 6 pots of the middle row for each cultivar were the core plots that were sampled in both experiments and each pot was treated as a replicate. Consequently, the sampled pots had a guard of at least 1 pot in each direction. The last fully expanded leaf (the leaf with the most recently emerged dewlap) was marked with a marker pen on each stalk when transferred to the compartments. Temperature treatments Both compartments were set at 25◦ C until 14 November 2000 when temperature regimes detailed in Table 1 were initiated. The temperature regimes were developed from long-term averages of maximum, minimum, and temperatures at 9.00 a.m. from meteorology stations at Kimberly Research Station, Kununurra (15◦ 39 S 128◦ 42 E; Ord River district), and Ayr Post Office (19◦ 35 S, 147◦ 24 E; Burdekin River district) (Bureau of Meteorology 1988), and hourly temperature averages collected by automatic weather stations at Cummings Farm, Kununurra (15◦ 39 S 128◦ 43 E), and DPI Ayr Station (19◦ 36 S,
Time
05:00 09:00 12:00 14:00 17:00 19:00 22:00
Higher temp. (◦ C) Nov. Dec. 24.7 32.8 38.7 38.7 33.0 29.0 26.5
25.0 32.0 37.8 37.8 32.0 28.0 26.5
Time
Lower temp. (◦ C) Nov. Dec.
02:00 06:00 09:00 13:00 15:00 18:00 20:00 23:00
22.5 21.5 28.1 31.9 31.9 29.0 26.0 24.0
23.0 22.4 28.9 32.7 32.7 29.5 26.5 24.5
147◦ 26 E). The profiles for November were used from 14 November 2000 to 6 December 2000 and then the profiles for December were used until the plants were harvested during 12–16 January 2001. Plants were watered to field capacity 3 times a day.
Experiment 2. Effect of temperature on ratooning cane The plants from Expt 1 were allowed to regenerate from subterranean buds (ratoon) in the same controlled-environment compartments. Plants were subjected to the December temperature regimes (Table 1) for the duration of Expt 2. Plants were treated for mite infestation on 22 May 2001 using Disyston (Bayer) according to the manufacturer’s instructions. Sampling stalks in Expt 2 Sampling was conducted on 17 July 2001 (Q158) and 18 July 2001 (Q117) soon after Q158 started to sprawl in the compartment with the higher temperature. As for Expt 1, the 4 tallest stalks were processed as follows. The height to the last fully expanded leaf and the number of nodes were recorded. Internodes enclosed (subtended) by leaves 4, 8, 12, and 20, below the last fully expanded leaf, were removed. Internode measurements and subsampling was as for Expt 1.
Temperature effects on composition of sugarcane
Australian Journal of Agricultural Research
Sucrose and fibre content
40 (a)
For both experiments, a subsample of the frozen tissue was extracted in 9.76 mL of 80% ethanol at 75◦ C for 6 h. The solution was decanted and both extract and stem segments frozen at −20◦ C. The next day a second extraction in 9.80 mL of water at 60◦ C for 6 h followed. The extracts were combined and stored at −20◦ C. The internode material remaining after extraction was dried at 60◦ C and then weighed as the insoluble fraction – an estimate of fibre. Sucrose, glucose, and fructose were measured by HPLC using the method of Bonnett et al. (2001).
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30
25
Thermal time Thermal time (degree-days) was calculated, using a base temperature of 9◦ C with either (i) a linear rate of accumulation of thermal time to 32◦ C then a linear decrease at temperatures above 32◦ C reaching 0 at 45◦ C (Inman-Bamber 1994; Bonnett 1998; Robertson et al. 1998) or (ii) with no reduction in the accumulation of thermal time above 32◦ C.
Measurements for whole stalks or of the selected internodes were compared between the 2 temperature regimes for each cultivar separately using 1-way analysis of variance. It is acknowledged that the effects of compartment could not be isolated as the treatments could not be repeated; however, a similar aerial environment was achieved by only sampling plants that were guarded by a row of plants on both sides and at the ends.
Results
20 (b) 35
Temperature (°C)
Statistical analysis
30
25
20
Differences in the temperature regimes Representative temperatures for Expts 1 and 2 are shown in Fig. 1. In Expt 1, the controlled temperatures followed the mean diurnal patterns closely (
