Some Physiological Parameters and Sugar Concentration Changing of Sugar Beet (Beta vulgaris L.) Under Controlled Climatical Conditions
Z. Shojaei Asadiyeh
This research was conducted to investigate the impact of night temperature and light intensity on growth indices and sugar content of sugar beet (Triploid Multigerm Iran-Karaj 1 variety, type N-E) in a Mediterranean climate (North West of Iran) at Moghan Agro-industry and Livestock Co.
from April 2001 to February 2002. Its lower sugar contents were reported
than those normally grown in other sugar beet growing regions. Sugar beet
crops were cultivated with full automatic controlled environment (night
temperature and light intensity) facilities in an experimental farm. Data
were collected 80 days after planting using a completely randomized block
design with four replications using 7 treatments. The treatments consisted
of night temperature 15°C (T1) and 10°C (T2),
increase of light intensity (L), night temperature 15°C and increase
of light intensity (T1L), night temperature 10°C and increase
of light intensity (T2L), a greenhouse control (C1)
and a control without greenhouse (C2). The total dry matter
and leaves area of sugar beet were measured to calculate the growth indices
including shoot crop growth rate, total crop growth rate, leaf area index
and net assimilation rate from 20 days after planting. After 140 days,
some samples were taken from the roots of sugar beet and pulp in order
to determine the sugar content. This sampling procedure was carried out
every 10 days up to 210 days after planting. Model development showed
that the best equation, Y = aebx (Y is the sugar content, e,
the napery logarithm, a and b are coefficient and x is one of the growth
indices), was obtained from data regression. The growth indices were negatively
correlated well (p<0.001) with sugar content. Hence, the low sugar
content could be due to the warm nights and slight light intensity during
It is well documented that the quality and quantity of economic plants such
as sugar beet (Beta vulgaris L.) has increased noticeably due to improvements
in agronomy and genetic (Fabeiro et al., 2003).
One of major concerns for agricultural plants is to study growth physiology
of crop yield (Freeckleton et al., 1999; Scott
and Jeggard, 2000) and physiological growth patterns (Bedell
et al., 2006). The relationship between growth indices and sugar
content of sugar beet in a controlled environment temperature and light intensity
has been studied (Ulrich, 1952). Ulrich
(1952) found the sugar content of Sugar beets was 15.4% at 17°C and
18.3% at 10 and 4°C night temperature. Multi factors such as climate, soil
texture, nutrient availability and the occurrence of pests and diseases and
their interactions can affect crop growth (Jones et al.,
2003; Sivakumar, 2006;Qi et
al., 2005; Kenter and Hoffmann, 2006). To date,
various attempts have been carried out to study impacts of temperature changes,
solar radiation and water input on the growth and development of sugar beet
(Abdollahian-Noghabi and Froud-Williams, 1998; Kenter
et al., 2006). No general conclusions of crop growth can be obtained
from individuals to match other climatic regions. For example, temperature has
an effect on the early growth of sugar beet in Central Europe (Durr
and Boiffin, 1995) and there was a relationship between the crop growth
rate and absorbed solar radiation after canopy closure in the UK (Scott
and Jaggard, 1993). Most recent works has been done to quantify the influence
of temperature, solar radiation and water supply on sugar beet growth (Clover
et al., 2001; Kenter and Hoffman, 2006). Even
though published data exist on the effects of agronomic ways such as irrigation
and fertilization on sugar beet quantitative and qualitative analysis of the
roots (Fabeiro et al., 2003), there is still limited
data on sugar beet physiology (Yadollahi, 1998). Yet, the
prime factor for sugar yield of sugar beet is low sugar content of roots in
warm Mediterranean climate such as north West of Iran-Moghan. Yadollahi
(1998) studied the effects of night temperature and light intensity on producer
molasses in warm Mediterranean climate. It was found that the producer molasses
decreased since the night temperatures were adjusted within 10-15°C in nights
and light intensity, 30000 Lux in days. Sugar beets cultivating under warm Mediterranean
climate in Iran-Moghan Plain has real problem as low sugar content (8-10%) which
is unacceptable in crop management.
MATERIALS AND METHODS
A two-year experiment (2001-2002) was carried out in a commercial farm located
in the North West of Iran with a warm Mediterranean climate. Some agronomic
characteristics of the farm were consisted of the geographical location (50
m above sea level), site (39°23′-39°42′ N and 47°25′-48°23′
E), fertilization (300 kg t-1, phosphate ammonium and urea, 100 kg
t-1), mean temperature (°C) (Tmin, 8.6 and Tmax,
20.7), mean (Tmax-Tmin) (12.1°C), total cloudy day
(141 days). The other characteristics were light intensity (15000-25000 Lux),
mechanized planting systems, farm position (research site), irrigation (from
Arras river) and soil (clay). A variety of triploid Multigerm Iran-Karaj 1,
type N-E was selected for planting in the experimental farm (area, 70x60 m2).
Seeds were planted in 4 rows from 60 cm apart and the distance between the plants
was 15 cm. Thereafter, the farm was watered. The date of planting in 2001 was
6th April and the second year was 6th February. Enough fertilization was used
as basal and top-dressing (Table 1). After establishment of
experimental plots, 24 greenhouses (volume: 75 cubic meter) were made to control
night temperature and increase the light intensity after 80 DAP. A ventilation
apparatus was installed in each greenhouse. The frame of greenhouse was made
of galvanized pipes which can be easily set up. There was used 16 cooler (0-General
18000, USA) with thermostat and automatic timer set up in order to control night
temperature. For increasing the light intensity (approximately 30000 Lux), supplementary
lightning was provided using 12 reflective fluorescent tubes above crops (1.20
m) from 7 am to 7 pm.
||Summary of statistical evaluation of sugar yield data in year
2002; ANOVA, a Duncan′s test
|Means of four replicates in the same column followed
by different letter(s) are significantly different according to Duncan′s
test at p<0.01
To supply electricity with automatic timer set up in the greenhouses, digging
channels and setting cables (35x16) in 1.2 m depth between blocks of design were
done and then install the main electricity transformer. After 80 days, the controlled
of night temperature was applied as well as increasing light intensity during
day time. Sampling procedure was carried out to obtain experimental data including
20 DAP (for dry matter, area of leaves in relation to crop growth rate of shoot
(CGR-Shoot), CGR-Total, Leaf Area Index (LAI) and Net Assimilation Rate (NAR),
140 DAP (for obtaining sugar concentration from roots and pulps of sugar beet).
This sampling procedure (at the date of 140 DAP) was repeated every 10 days till
210 DAP. Each sample was taken from 1 m of middle rows. The shoots were cut from
the roots and were washed and made up pulps with the weight of 100 g for each
treatment. The sugar beet pulps were kept in a freezer (-20°C) to use for
all analysis subjects to this research in the modern sugar beet laboratory in
Ministry of agriculture, Tehran-Karaj. A completely randomized block design with
four replications and seven treatments were used to obtain data after 80 Days
After Planting (DAP).
Measuring Sucrose Concentration
Determination of sugar beet root quality was conducted using a Betalyser (Dr.
Wolfgang Kernchen GMBH, Seelz, Germany). The pulp, 26 ± 0.05 g, was added
to 177 mL of Aluminium Sulphate (Sigma Alderich, UK). The solution was centrifuged
(12000-15000 rpm for 3 min) and the supernatant was extracted for measuring
sugar content by direct polarization at 20°C (Method GS6-3,
Determination of Sugar Yield
Sugar yields are as a result of root yield and sucrose concentration (Werker
and Jaggard, 1998). Therefore, to calculate sugar yield, net sugar content
(sugar) of crop is obtained from Eq. 1:
where, the MS expresses sugar concentration of molasses and Pol indicates
sugar concentration of root measuring using a Polar meter. Then sugar
yield can be calculated by Eq. 2:
Sugar yield = (sugar/pol)x100
A formal model as reported by Rafiei (1995) illustrates well
the crop growth rate. Hence, the crop growth rate of the sugar beet is calculated
using the Eq. 3.
where, Y is the weight of Dry Matter (DM) and x express DAP and a, b,
c and d represent coefficients of Eq. 3. The RGR is a
relative growth rate and can be obtained from Eq. 4:
RGR = (logw2
where, logw2 and logw1 are the weight of crop (in
logarithm scale) at the harvesting time (t1) and when the crop
was dried (t2), respectively. Other parameters such as CGR
and NAR were given as below:
The LAI is defined as the total leaf area of a crop per unit area of
soil surface (m2 m-2). A direct method has been
used to measure LAI using a LAI-2000 Plant Canopy Analyzer (Li-cor).
Statistical Analysis of Data
Statistical analyses were performed with SPSS 13.0 (SPSS, Inc., New Jersey,
USA). The experimental design was a randomized complete block with four
replicates. Data was subjected to ANOVA using a Duncan′s test to analyze
differences between seven treatments (at four dates consisting of 1st,
11th, 21st September and 1st October 2002).
RESULTS AND DISCUSSION
The results of statistical evaluation (ANOVA, a Duncan′s test, Table
1) showed that significant differences were found between seven treatments
in the four dates consisting of 1st, 11th, 21st September and 1st October
2002. The T1 treatment had maximum sugar concentration of root,
8.65 t ha-1. Careful consideration of data analysis indicates
that sugar yield data were greatest for majority of treatments in 21st
September, whereas the two treatments, C1 and C2, had lowest values of
sugar yield. As a result, higher sugar yield could be achieved when shoot
crop growth rate values will be more negative.
Correlation Between Growth Indices and Sugar Content of Sugar Beets
CGR-Shoot and Sugar Content
The relationship between CGR-Shoot and sugar concentration is shown in the Fig.
1 in 2001. The regression equation in the common form of y = ae-bx
was obtained from regression analysis of two sets of data, experimental and
theoretical data as follows:
where, SP is a sucrose concentration (in percentage), e is a napery logarithm
and CGRsh, is a shoot CGR (g m-2 day-1).
The coefficient correlation (R2) was found 0.86 (significant
at the p<0.001 level).
||Relationship between CGR values and sugar concentrations in
The CGR-Shoot values inversely correlated with sucrose concentrations
in 2001. It was obtained 14.7 for sucrose concentration with 2.2 g m-2
day-1 CGR shoot occurrence. The relationship between CGR-Shoot
and sugar concentration (Fig. 2) in 2002, shows a negative
correlation between CGR and sugar content of shoot in 2002 (based on the
equation 7) and The R2 was obtained 0.8 (significance level
Correlation Between the CGR-Total and Sugar Content
Figure 3 showed that the relationship between total
crop growth rate and sugar content in 2001.
||The relationship between sugar concentration and CGR
||Total CGR data were plotted versus sugar concentration
||Total CGR data were plotted versus sugar concentration
The best regression equation was found to be as given below:
The R2 was obtained 0.9 (significance level p<0.001) with
a negative correlation. The sugar content of 14.7 with total CGR 1.5 g
m-2 day-1 was obtained for the first year. In the
second year, the relationship between total CGR and sugar content was
similar to that of the first year (Fig. 4) with an equation
as given below:
Figure 4 shows the negative relationship between CGR shoot
and sugar percentage (R2 = 0.9 at p<0.001) in 2002. The sugar concentration
was 19.7 with total CGR 1.6 g m-2 day-1. While the total
crop growth rate was found 1.5 g m-2 day-1 with a sugar
content of 14.7 in the experimental farm, the total growth rate of Isfahan area
(Rafiei, 1995) was reported -20 g m-2 day-1
with sugar concentration of 20. Therefore, to gain higher sugar content, it
is required to maintain the total CGR low in August and September. This is consistent
with the findings of Tsukada and Takada (1988) who confirmed
a negative relationship between total growth rate and sugar concentration of
sugar beet based on the qualitative evaluation of sugar beet.
Correlation Between LAI and Sugar Content
The negative relationship between LAI and sugar content (2002) was shown
in Fig. 5. From the regression analysis, the best equation
was obtained as follows:
In Eq. 10 the coefficient was 0.80 which was significant
at P< 0.001 level. This imply that the LAI values around 3-4 would be suitable
to gain higher sugar content. This is in agreement to the findings of Ulrich
(1961) who reported LAI 4 and high sugar content 17.2 in a controlled system.
Others concluded that the normal LAI 6-7 resulted in sugar content of 8-12 (Yadollahi,
1998). As a result, the appropriate variety of sugar beet and suitable farming
methods may decrease LAI to a desirable level (i.e., 4).
||Observed LAI values and sugar concentration (%)
||Observed NAR values and sugar concentration (%)
NAR and Sugar Content
The relationship between net assimilation rate and sugar content after
140 till 210 DAP in 2002 was shown in Fig. 6. The regression
relationship between net assimilation rate and sugar content was calculated
as given below (Eq. 11, R2 = 0.7 at p<0.001):
There is reverse correlation between NAR values and sugar content which suggests
that when NAR values increase, sugar concentrations will reduce. The greatest
value of NAR is about 0.4-0.6 g m-2 day-1 which is similar
to the literature values (Ulrich, 1952; Miyazawa
et al., 2004; Javaheri et al., 2004).
The sucrose concentration of sugar beet increased from 14.7 (CGR-Shoot, -2.2
g m-2 day-1) in 2001 to 19.7 (CGR-Shoot, -2.4 g m-2
day-1) in 2002. To achieve higher sucrose concentration, it seems
that the CGR-Shoot is of prime importance. The highest sugar concentration 14.7
in year 2001 was related to CGR -2.2 g m-2 day-1 obtained
from a treatment with night temperature of 15°C (T1) 190 DAP
(11th of September in 2001) also in year 2002, the highest sugar concentration
was 19.7 related to CGR -2.4 g m-2 day-1 obtained from
a treatment with night temperature of 15°C (T1) 190 DAP (11th
of September in 2002). The results showed that the CGRshxday values
(when CGR values become negative), has not gone up more than -108 g m-2.
Nevertheless, the report by Rafiei (1995) pointed out that
the CGRshxday values reached to -20 g m-2 since CGR values
become negative until the time of crop harvesting, obtaining sugar concentration
of 20. Although there is a relationship between negative CGR and, yellowing
and falling of leaves and leaf stalk, transportation of carbohydrates from shoot
to root causes an increase of the CGR. The period of CGRsh would
decrease with additional constituents of the CGRsh product. Thus,
if the time of crop harvesting delays, the sugar content decrease. It should
be noted that by using growth inhibiting substrates (Ulrich,
1952) the shoot CGR in months August and September of crop harvesting decrease
before crop harvesting. Consequently, the root yield and sucrose concentration
have an effect on sugar yields (Werker and Jaggard, 1998).
In addition to that, applying some furring method such as raining irrigation
produces lower night temperature. The more negative CGR would be better condition
for higher sucrose accumulation in roots. Possibly varieties that physiologically
have negative CGR could be a good substitute to obtain higher sugar content.
Moreover, the extent of light intensity could be accountable for modification
of sugar concentration.
Sugar beet is capable and temperate crop readily settled in different environmental
conditions. On the other hand, the properties of sugar beet roots are influenced
by climatic conditions (Ritcher et al., 2001).
For instance, good quality roots in terms of high sugar content can be generated
if the plant is cultivated with favourable climatic such as temperate and sunlight,
sugar production is directly proportional to the sunlight interception over
time by the leaf canopy (Ulrich, 1961). The result obtained
from this research which done in the real farm with facilities of controlled
area systems for temperate and sunlight over the canopy, exactly confirmed by
the above research and model evaluations under temperate and sunlight conditions
in this research showed that growth indices values were inversely correlated
well to sugar concentration of sugar beet on the warm Mediterranean climate.
According to this result, there is possible to increase sugar content in warm
Mediterranean climate with the employs of some techniques to bring down the
night temperate 80 days after planting and increase light intensity in the same
period in day time.
The authors gratefully thank Ministry of Agriculture for financial
support of this project (Grant No. 42/326/8719).
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