Directory UMM :Data Elmu:jurnal:S:Scientia Horticulturae:Vol86.Issue3.Nov2000:
Scientia Horticulturae 86 (2000) 185±195
Frost sensitiveness of chicory roots
(Cichorium intybus L.)
V. Neefs*, S. Leuridan, N. Van Stallen,
M. De Meulemeester, M.P. De Proft
Faculty of Agricultural and Applied Biological Sciences, Department of Applied Plant Sciences,
Laboratory for Plant Culture, Katholieke Universiteit Leuven, Willem de Croylaan 42,
B-3001 Heverlee, Belgium
Accepted 16 February 2000
Abstract
This study was conducted to determine if chicory roots (Cichorium intybus L. var. foliosum) can be
stored at temperatures below ÿ18C. Roots from cultivar Focus, produced in hydroponics on two
different arti®cial substrates, were stored at ÿ1, ÿ2.5, ÿ5 and ÿ78C. After storage at sub-zero
temperatures, roots with highest dry weight percentage showed highest chicon production and highest
organogenesis capacity. Moreover, the electrical resistance of those roots never decreased signi®cantly
during storage, while roots with a lower dry weight percentage had reduced electrical resistance after
storage at ÿ78C. Decrease in electrical resistance was detected before frost damage became visible.
Thus, measuring the electrical resistance of root tissue can be used to predict frost damage. The most
distinct frost damage symptoms were `water soaking' and browning of the vascular bundles. According
to these results, it can be concluded that storage temperatures below ÿ18C, but above ÿ78C, are not
necessarily fatal for chicory roots: roots with relatively high dry weight percentage are best able to
withstand low storage temperatures. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Chicory roots; Frost damage; Dry weight percentage; Plant electrical resistance;
Storage
1. Introduction
Chicory, Cichorium intybus L. var. foliosum, is a biennial plant. After the ®rst
growing season chicory roots are harvested, cold stored and forced in the dark.
*
Corresponding author. Tel.: 32-1632-2390; fax: 32-1632-2966.
E-mail address: veerle.neefs@agr.kuleuven.ac.be (V. Neefs).
0304-4238/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 0 4 - 4 2 3 8 ( 0 0 ) 0 0 1 5 0 - 3
186
V. Neefs et al. / Scientia Horticulturae 86 (2000) 185±195
Root reserves are remobilised during the forcing process to support the growth of
an etiolated head, the chicon, which is marketed. To ensure a continuous supply
on the market, cold storage of chicory roots is a requirement. For long storage,
chicory roots are kept at ÿ0.5 to ÿ18C (Scheer, 1997). Nevertheless, lower
storage temperatures would improve storage duration, if frost damage can be
avoided. In the present work, storage of chicory roots at four different sub-zero
temperatures has been examined to determine when frost damage occurs.
2. Materials and methods
2.1. Plant material: growth and storage conditions
Chicory seeds (Cichorium intybus L. var Foliosum cv. `Focus') were sown in
hydroponics (May 1997) on two different arti®cial substrates. One substrate (50/
50 substrate) was a mixture of 50% hydrophilic (Grodan type 012/519) and 50%
hydrophobic rock wool (Grodan BU 20 granulate). The other substrate (100/
Argex substrate) was pure hydrophilic rock wool with clay granules (Argex, 0.5±
1 cm diameter) underneath to avoid root waterlogging. Plants were fertigated
three times a day (at 9.00, 12.00 and 16.00 hours) with 100 ml nutrient solution
per root. A solution with 50 mval/l ionic strength (De Rijck et al., 1993) was used
for the ®rst 6 weeks, thereafter a solution with 16 mval/l ionic strength (solution
number 4 (De Rijck et al., 1993)). Because plants can be made more tolerant to
sub-zero temperatures by stress treatments (Biddington and Dearman, 1988;
Gusta et al., 1996), plants received only 100 ml nutrient solution once in a day, at
9.00 hours the last 6 weeks before harvest. Roots were harvested at the beginning
of October 1997 and stored at 18C for 20 days. Afterwards, they were placed in
four different storage rooms where root temperatures of, respectively, ÿ1.06,
ÿ2.59, ÿ5.00 and ÿ6.898C were reached within 14 days. Temperatures were
continuously recorded (Escort Junior, VEL) over a 76 day experimental storage
period.
2.2. Dry weight percentage
Dry weight percentage (% DW) of root tissue was determined by drying fresh
root tissue for 1 week at 808C.
2.3. Evaluation of stored roots
After 34 and 76 days storage 30 roots of each substrate were taken from each
temperature treatment for analysis. Because 1 week thawing at a low positive
temperature is advised (Scheer, 1997), roots were placed at 28C. Afterwards,
V. Neefs et al. / Scientia Horticulturae 86 (2000) 185±195
187
roots were conditioned at room temperature for 24 h and evaluated. For the
evaluation, roots were divided into two parts by a transverse cut 3 cm below the
apex. The upper part was used for chicon production, the lower part for all other
evaluations.
2.3.1. Chicon production
After disinfection with benomyl (0.5 g/l), the upper parts of the roots were forced
on white sand and tap water (dark, 168C). After 14 days chicory heads (chicons)
were harvested. Weight and core length of the chicons were measured. Chicons
produced on control roots (kept 20 days at 18C) were evaluated the same way.
2.3.2. Plant electrical resistance
A plant electrical resistance meter (Resamet RM-90, Nieuwkoop B.V.,
Aalsmeer) was used to measure the electrical resistance (ER) of central
parenchyma, vascular bundles and cortical parenchyma on the transverse section
of the lower root parts. Frost damage of plant tissues is associated with a decrease
in ER (Zhang and Willison, 1990, 1992a,b; Prive and Zhang, 1996).
2.3.3. Organogenesis capacity
A 1 cm thick root disc was taken from each root 5 cm below the apex. After
disinfection with benomyl (0.5 g/l), these root discs were placed on sterile sand
and tap water in miniature greenhouses (45 cm30 cm15 cm) under long day
conditions (16 h light, 228C). After 18 days, organogenesis was evaluated by
counting the number of shoots and weighing the proliferated mass of the
cambium ring.
2.4. Statistical analysis
Each time all measurements were done on 30 roots. The in¯uence of the
combined effect of substrate, storage duration and storage temperature was tested
on all evaluation parameters except for the parameters expressed in percentage.
To ®nd signi®cant differences in ER the Duncan's Multiple Range Test was used.
In the case of chicon evaluation, the number of roots that produced a chicon
determined the sample size of the other evaluation parameters (chicon weight,
core length). Thus, the sample size itself depends on the treatment. Because the
differences in sample size were large, it was necessary to use the Tukey's
Studentised Range Test to determine the in¯uence of the combined effect on
chicon weight and core length. The same remark is valid for the evaluation of root
disc organogenesis capacity. In this case the proportion of root discs that
produced shoots determined the sample size. For parameters expressed in
percentage, the in¯uences of substrate, storage duration and storage temperature
were tested separately with the Chi-square-test. Only signi®cant in¯uences with a
188
V. Neefs et al. / Scientia Horticulturae 86 (2000) 185±195
strong correlation (uncertainty coef®cient symmetric, UCS>0.1) are mentioned.
For each statistical analysis a signi®cance level of 5% was maintained.
3. Results
3.1. Temperature progress during cooling
Harvested roots were ®rst kept at 18C for 20 days. Afterwards they were
placed in four different storage rooms. It took about 2 weeks before the roots
reached their ®nal temperatures of ÿ1.06, ÿ2.59, ÿ5.00 and ÿ6.898C, respectively.
3.2. Characterisation of the roots
Roots cultivated on the 50/50 substrate were smaller (mean diameter: 33 mm,
mean weight: 133 g) than roots from the 100/Argex substrate (mean diameter:
37 mm, mean weight: 157 g). Reducing the amount of hydrophilic rock wool (50/
50 substrate) resulted in roots with a signi®cantly (Duncan's Multiple Range Test,
a0.05) lower dry weight percentage (28.3% DW) than those that were grown on
100% hydrophilic rock wool (100/Argex substrate, 30.4% DW).
3.3. Evaluation of stored roots
3.3.1. Chicon production
The in¯uence of storage temperature and duration on the number of roots still
producing a chicon was signi®cant with a strong correlation (UCS, respectively,
0.179 and 0.103). Cold storage at ÿ18C and lower reduced the number of roots
which are capable to form a chicon (Table 1). Roots grown on the 50/50 substrate
did not produce any chicons after 34 days at ÿ78C and 76 days at ÿ5 or ÿ78C.
On the other hand, roots cultivated on the 100/Argex substrate still produced
chicons in all cases, but the number of roots with a chicon also decreased with
decreasing temperature and increasing storage duration. Roots with higher % DW
were more resistant to low temperature treatments.
The weight of chicons produced on control roots (20 days stored at 18C) grown
on the 50/50 substrate was signi®cantly higher than the weight of all chicons
produced on roots of both substrates after 76 days cold storage. The weight of all
chicons produced on roots from the 50/50 substrate after 34 days cold storage was
signi®cantly higher than the weight of all chicons produced on roots from the same
substrate but after 76 days cold storage. The weight of chicons produced on roots,
grown on the 100/Argex substrate, after 34 days storage at, ÿ1, ÿ5 and ÿ78C,
respectively, was signi®cantly higher than the weight of chicons grown on roots from
the same substrate, but after 76 days storage at the same temperatures.
189
V. Neefs et al. / Scientia Horticulturae 86 (2000) 185±195
Table 1
Evaluation of chicon production on roots from cv. Focus, after 20 days at 18C followed by a cold
treatment of 0, 34 and 76 days at different temperatures
Root
Days
Storage
growth
cold
temperature roots with
substrate
treatment (8C)
50/50
Weight of chicon (g)
Core length (mm)
chicon
Mean
Tukey
Mean
100
Tukey
0
±
22.2
D
B
9.8
34
ÿ1.06
86.7
24.9
A
B
20.6
A
B
ÿ2.59
73.3
31.6
A
21.1
A
B
ÿ5.00
33.3
23.2
A
13.5
D
E
F
ÿ6.89
0.0
±
ÿ1.06
50.0
9.8
G
E
14.5
D
E
F
ÿ2.59
50.0
10.9
G
E
12.6
D
E
F
G
ÿ5.00
0.0
±
±
ÿ6.89
0.0
±
±
0
±
96.7
19.0
D
B
C
F
G
34
ÿ1.06
93.3
20.2
D
B
C
16.3
D
E
C
ÿ2.59
90.0
19.6
D
B
C
17.1
D
B
C
ÿ5.00
66.7
15.0
D
B
C
E
ÿ6.89
30.0
19.6
D
B
C
E
76
100/Argex
% of
76
C
G
G
±
F
F
11.3
9.8
23.1
A
D
12.7
G
ÿ2.59
56.7
14.0
G
ÿ5.00
16.7
3.2
G
5.2
ÿ6.89
30.0
6.4
G
8.4
ÿ1.06
100
B
F
C
C
E
F
16.2
E
F
12.3
F
G
F
G
E
E
G
F
G
The chicon length was in¯uenced by the cold treatment: frost sensitive roots
produced smaller chicons (not exactly measured), which had relatively smaller
cores. To use the core length as a frost damage parameter it is necessary to
express it as a ratio to the chicon length. Because chicon length was not
measured, core lengths could not be compared.
Neither substrate, nor storage duration, nor storage temperature had a signi®cant
in¯uence with a strong correlation on percentage white chicons, percentage closed
chicons or percentage chicons with white core (data not shown). Nevertheless, there
was a weak trend (UCS
Frost sensitiveness of chicory roots
(Cichorium intybus L.)
V. Neefs*, S. Leuridan, N. Van Stallen,
M. De Meulemeester, M.P. De Proft
Faculty of Agricultural and Applied Biological Sciences, Department of Applied Plant Sciences,
Laboratory for Plant Culture, Katholieke Universiteit Leuven, Willem de Croylaan 42,
B-3001 Heverlee, Belgium
Accepted 16 February 2000
Abstract
This study was conducted to determine if chicory roots (Cichorium intybus L. var. foliosum) can be
stored at temperatures below ÿ18C. Roots from cultivar Focus, produced in hydroponics on two
different arti®cial substrates, were stored at ÿ1, ÿ2.5, ÿ5 and ÿ78C. After storage at sub-zero
temperatures, roots with highest dry weight percentage showed highest chicon production and highest
organogenesis capacity. Moreover, the electrical resistance of those roots never decreased signi®cantly
during storage, while roots with a lower dry weight percentage had reduced electrical resistance after
storage at ÿ78C. Decrease in electrical resistance was detected before frost damage became visible.
Thus, measuring the electrical resistance of root tissue can be used to predict frost damage. The most
distinct frost damage symptoms were `water soaking' and browning of the vascular bundles. According
to these results, it can be concluded that storage temperatures below ÿ18C, but above ÿ78C, are not
necessarily fatal for chicory roots: roots with relatively high dry weight percentage are best able to
withstand low storage temperatures. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Chicory roots; Frost damage; Dry weight percentage; Plant electrical resistance;
Storage
1. Introduction
Chicory, Cichorium intybus L. var. foliosum, is a biennial plant. After the ®rst
growing season chicory roots are harvested, cold stored and forced in the dark.
*
Corresponding author. Tel.: 32-1632-2390; fax: 32-1632-2966.
E-mail address: veerle.neefs@agr.kuleuven.ac.be (V. Neefs).
0304-4238/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 0 4 - 4 2 3 8 ( 0 0 ) 0 0 1 5 0 - 3
186
V. Neefs et al. / Scientia Horticulturae 86 (2000) 185±195
Root reserves are remobilised during the forcing process to support the growth of
an etiolated head, the chicon, which is marketed. To ensure a continuous supply
on the market, cold storage of chicory roots is a requirement. For long storage,
chicory roots are kept at ÿ0.5 to ÿ18C (Scheer, 1997). Nevertheless, lower
storage temperatures would improve storage duration, if frost damage can be
avoided. In the present work, storage of chicory roots at four different sub-zero
temperatures has been examined to determine when frost damage occurs.
2. Materials and methods
2.1. Plant material: growth and storage conditions
Chicory seeds (Cichorium intybus L. var Foliosum cv. `Focus') were sown in
hydroponics (May 1997) on two different arti®cial substrates. One substrate (50/
50 substrate) was a mixture of 50% hydrophilic (Grodan type 012/519) and 50%
hydrophobic rock wool (Grodan BU 20 granulate). The other substrate (100/
Argex substrate) was pure hydrophilic rock wool with clay granules (Argex, 0.5±
1 cm diameter) underneath to avoid root waterlogging. Plants were fertigated
three times a day (at 9.00, 12.00 and 16.00 hours) with 100 ml nutrient solution
per root. A solution with 50 mval/l ionic strength (De Rijck et al., 1993) was used
for the ®rst 6 weeks, thereafter a solution with 16 mval/l ionic strength (solution
number 4 (De Rijck et al., 1993)). Because plants can be made more tolerant to
sub-zero temperatures by stress treatments (Biddington and Dearman, 1988;
Gusta et al., 1996), plants received only 100 ml nutrient solution once in a day, at
9.00 hours the last 6 weeks before harvest. Roots were harvested at the beginning
of October 1997 and stored at 18C for 20 days. Afterwards, they were placed in
four different storage rooms where root temperatures of, respectively, ÿ1.06,
ÿ2.59, ÿ5.00 and ÿ6.898C were reached within 14 days. Temperatures were
continuously recorded (Escort Junior, VEL) over a 76 day experimental storage
period.
2.2. Dry weight percentage
Dry weight percentage (% DW) of root tissue was determined by drying fresh
root tissue for 1 week at 808C.
2.3. Evaluation of stored roots
After 34 and 76 days storage 30 roots of each substrate were taken from each
temperature treatment for analysis. Because 1 week thawing at a low positive
temperature is advised (Scheer, 1997), roots were placed at 28C. Afterwards,
V. Neefs et al. / Scientia Horticulturae 86 (2000) 185±195
187
roots were conditioned at room temperature for 24 h and evaluated. For the
evaluation, roots were divided into two parts by a transverse cut 3 cm below the
apex. The upper part was used for chicon production, the lower part for all other
evaluations.
2.3.1. Chicon production
After disinfection with benomyl (0.5 g/l), the upper parts of the roots were forced
on white sand and tap water (dark, 168C). After 14 days chicory heads (chicons)
were harvested. Weight and core length of the chicons were measured. Chicons
produced on control roots (kept 20 days at 18C) were evaluated the same way.
2.3.2. Plant electrical resistance
A plant electrical resistance meter (Resamet RM-90, Nieuwkoop B.V.,
Aalsmeer) was used to measure the electrical resistance (ER) of central
parenchyma, vascular bundles and cortical parenchyma on the transverse section
of the lower root parts. Frost damage of plant tissues is associated with a decrease
in ER (Zhang and Willison, 1990, 1992a,b; Prive and Zhang, 1996).
2.3.3. Organogenesis capacity
A 1 cm thick root disc was taken from each root 5 cm below the apex. After
disinfection with benomyl (0.5 g/l), these root discs were placed on sterile sand
and tap water in miniature greenhouses (45 cm30 cm15 cm) under long day
conditions (16 h light, 228C). After 18 days, organogenesis was evaluated by
counting the number of shoots and weighing the proliferated mass of the
cambium ring.
2.4. Statistical analysis
Each time all measurements were done on 30 roots. The in¯uence of the
combined effect of substrate, storage duration and storage temperature was tested
on all evaluation parameters except for the parameters expressed in percentage.
To ®nd signi®cant differences in ER the Duncan's Multiple Range Test was used.
In the case of chicon evaluation, the number of roots that produced a chicon
determined the sample size of the other evaluation parameters (chicon weight,
core length). Thus, the sample size itself depends on the treatment. Because the
differences in sample size were large, it was necessary to use the Tukey's
Studentised Range Test to determine the in¯uence of the combined effect on
chicon weight and core length. The same remark is valid for the evaluation of root
disc organogenesis capacity. In this case the proportion of root discs that
produced shoots determined the sample size. For parameters expressed in
percentage, the in¯uences of substrate, storage duration and storage temperature
were tested separately with the Chi-square-test. Only signi®cant in¯uences with a
188
V. Neefs et al. / Scientia Horticulturae 86 (2000) 185±195
strong correlation (uncertainty coef®cient symmetric, UCS>0.1) are mentioned.
For each statistical analysis a signi®cance level of 5% was maintained.
3. Results
3.1. Temperature progress during cooling
Harvested roots were ®rst kept at 18C for 20 days. Afterwards they were
placed in four different storage rooms. It took about 2 weeks before the roots
reached their ®nal temperatures of ÿ1.06, ÿ2.59, ÿ5.00 and ÿ6.898C, respectively.
3.2. Characterisation of the roots
Roots cultivated on the 50/50 substrate were smaller (mean diameter: 33 mm,
mean weight: 133 g) than roots from the 100/Argex substrate (mean diameter:
37 mm, mean weight: 157 g). Reducing the amount of hydrophilic rock wool (50/
50 substrate) resulted in roots with a signi®cantly (Duncan's Multiple Range Test,
a0.05) lower dry weight percentage (28.3% DW) than those that were grown on
100% hydrophilic rock wool (100/Argex substrate, 30.4% DW).
3.3. Evaluation of stored roots
3.3.1. Chicon production
The in¯uence of storage temperature and duration on the number of roots still
producing a chicon was signi®cant with a strong correlation (UCS, respectively,
0.179 and 0.103). Cold storage at ÿ18C and lower reduced the number of roots
which are capable to form a chicon (Table 1). Roots grown on the 50/50 substrate
did not produce any chicons after 34 days at ÿ78C and 76 days at ÿ5 or ÿ78C.
On the other hand, roots cultivated on the 100/Argex substrate still produced
chicons in all cases, but the number of roots with a chicon also decreased with
decreasing temperature and increasing storage duration. Roots with higher % DW
were more resistant to low temperature treatments.
The weight of chicons produced on control roots (20 days stored at 18C) grown
on the 50/50 substrate was signi®cantly higher than the weight of all chicons
produced on roots of both substrates after 76 days cold storage. The weight of all
chicons produced on roots from the 50/50 substrate after 34 days cold storage was
signi®cantly higher than the weight of all chicons produced on roots from the same
substrate but after 76 days cold storage. The weight of chicons produced on roots,
grown on the 100/Argex substrate, after 34 days storage at, ÿ1, ÿ5 and ÿ78C,
respectively, was signi®cantly higher than the weight of chicons grown on roots from
the same substrate, but after 76 days storage at the same temperatures.
189
V. Neefs et al. / Scientia Horticulturae 86 (2000) 185±195
Table 1
Evaluation of chicon production on roots from cv. Focus, after 20 days at 18C followed by a cold
treatment of 0, 34 and 76 days at different temperatures
Root
Days
Storage
growth
cold
temperature roots with
substrate
treatment (8C)
50/50
Weight of chicon (g)
Core length (mm)
chicon
Mean
Tukey
Mean
100
Tukey
0
±
22.2
D
B
9.8
34
ÿ1.06
86.7
24.9
A
B
20.6
A
B
ÿ2.59
73.3
31.6
A
21.1
A
B
ÿ5.00
33.3
23.2
A
13.5
D
E
F
ÿ6.89
0.0
±
ÿ1.06
50.0
9.8
G
E
14.5
D
E
F
ÿ2.59
50.0
10.9
G
E
12.6
D
E
F
G
ÿ5.00
0.0
±
±
ÿ6.89
0.0
±
±
0
±
96.7
19.0
D
B
C
F
G
34
ÿ1.06
93.3
20.2
D
B
C
16.3
D
E
C
ÿ2.59
90.0
19.6
D
B
C
17.1
D
B
C
ÿ5.00
66.7
15.0
D
B
C
E
ÿ6.89
30.0
19.6
D
B
C
E
76
100/Argex
% of
76
C
G
G
±
F
F
11.3
9.8
23.1
A
D
12.7
G
ÿ2.59
56.7
14.0
G
ÿ5.00
16.7
3.2
G
5.2
ÿ6.89
30.0
6.4
G
8.4
ÿ1.06
100
B
F
C
C
E
F
16.2
E
F
12.3
F
G
F
G
E
E
G
F
G
The chicon length was in¯uenced by the cold treatment: frost sensitive roots
produced smaller chicons (not exactly measured), which had relatively smaller
cores. To use the core length as a frost damage parameter it is necessary to
express it as a ratio to the chicon length. Because chicon length was not
measured, core lengths could not be compared.
Neither substrate, nor storage duration, nor storage temperature had a signi®cant
in¯uence with a strong correlation on percentage white chicons, percentage closed
chicons or percentage chicons with white core (data not shown). Nevertheless, there
was a weak trend (UCS