Deutscher Tropentag 2003

Göttingen, October 8-10, 2003

Conference on International Agricultural Research for
Development

Effect of High Temperature and Heat Shock on Tomato (Lycopersicon esculentum Mill.)
Genotypes under Controlled Conditions

Adil H. Abdelmageeda, Nazim Grudab, Bernd Geyerb

a University of Khartoum, Department of Horticulture, Sudan

b Humboldt-Universität zu Berlin, Institute for Horticultural Science, Department of Vegetable Crops,
Lentzeallee 75, 14195 Berlin, Germany. Email: nazim.gruda@rz.hu-berlin.de

Abstract
Tomato (Lycopersicon esculentum MILL.) is usually produced during the winter period in
Sudan. In summer due to high temperatures, monthly average temperatures are between 31 to
35°C, a shortage of tomatoes is common. General environmental changes, especially global
warming, may have an adverse effect on crop production in Sudan.
The objective of this study is (i) to investigate the effect of heat stress on vegetative and
productive development of heat sensitive and tolerant tomato genotypes, (ii) to compare the
growth and development of different genotypes under defined heat stress conditions (intensity
and duration) as well as (iii) to investigate if there are any positive effects of heat shock
treatments to increase heat tolerance of tomatoes.
Different experiments were carried out under simulated temperature conditions in plant
growth chambers at the Humboldt University of Berlin as well as under field conditions at the
University of Khartoum, Sudan. Here only results obtained from experiments under controlled
condition are presented. Plant height, leaf area, fresh and dry weight of leaves, stem and roots,
number of clusters, number of flowers as well as the number of pollen grains per microscopic
field were recorded.
The reproductive processes in tomato were more sensitive to high temperatures than the
vegetative ones. The number of pollen grains produced by the heat tolerant genotypes, were
higher than the numbers produced by the heat sensitive genotypes.
However, under field condition around Khartoum, Sudan other factors such as low relative
humidity, insect and virus diseases as well as soil physical properties have also to be
considered. Optimization of microclimate could be very important to ensure a good
performance of new tolerant varieties cultivated in summer periods in Sudan.

Keywords: Heat stress, heat shock, pollen grains, summer period, Sudan, tolerant genotypes,
tomato.

Introduction

Tomato is one of the most popular and widely consumed vegetables grown worldwide.
Popularity of the crop stems from its acceptable flavour, nutritive value (high in vitamin C
and A), the short life cycle, and the high productivity. In the Sudan tomato ranks second to
onion among vegetable crops based on cultivated area. It is grown throughout the country
where irrigation water and arable land are available and is mainly grown by small holders
who employ relatively poor crop management practices.
In the arid tropical region of the Sudan the high summer and the low relative humidity limits
the production of tomato to the cooler period of the year. To extend the season of production
it is necessary to know the nature of growth, flowering and fruiting of the plant in relation to
climatic conditions (Abdalla and Verkerk, 1968). Heat stress (HS) is one of the most
important constraints on crop production and adversely affects the vegetative and
reproductive processes of tomato and ultimately reduces yield and fruit quality (Abdul-Baki,
1991). Moreover, a number of explanations have been offered for the poor reproductive
performance of tomatoes at high temperatures. These include reduced or abnormal pollen
production, abnormal development of the female reproductive tissues, hormonal imbalances,
low levels of carbohydrates, and lack of pollination (Abdalla and Verkerk, 1968; Peet et al.,
1997). Dinar and Rudich (1985) reported that in tomato plants, high temperatures affect
several physiological and biochemical processes dealing finally with yield reduction. Possible
biochemical and/or physiological processes affected by temperature are photosynthetic
enzyme activity, membrane integrity, photophosphorylation, and electron transport in
chloroplast, stomatal conductance to CO2 diffusion and photoassimilate translocation.

Plants respond to HS by changing their metabolic pathways. Under HS, synthesis of most
proteins is repressed and some proteins, which are called heat shock proteins (HSPs), start to
be synthesised (Vierling, 1991). Heat shock can be used as control of some plant diseases as
alternative for chemical control of vegetable seeds diseases (Jahn et al., 2000), as well as for
post harvest, to improve the quality of vegetables (Loaiza-Velarde and Saltveit, 2001 and
Loaiza-Velarde et al. 1997). Moreover, Yarwood (1961) demonstrated that leaves subjected to
high temperatures (50 °C) for short periods (15-30 s) tolerated high temperatures (55 °C)
longer than untreated leaves. Also, Lin et al. (1984) reported that soybean seedlings exposed
to 40 °C for 2 h produced HSPs and tolerate temperature of 45 °C, but plants transferred
directly from 28 to 45 °C did not produce HSPs. Chen et al. (1982) mentioned that tomato
plants grown in temperature regimes below 30 °C their leaf tissues were killed in about 15
min at 50 °C, while tomatoes plants increased significant tolerance when exposed to
temperatures above 30°C for 24 h.

The results of the above researchers led to the assumption that heat shock treatments on
tomatoes plants would be of benefit for tomato production under high temperature conditions.

The objectives of this study are (i) to investigate the effect of HS on vegetative and productive
development of different tomato genotypes under defined conditions (intensity and duration)
as well as (ii) to investigate if there are any positive effects of heat shock treatments to
increase heat tolerance of tomatoes.

Materials and Methods

Two heat tolerant cultivars and one less heat tolerant cultivar were selected for this study
(Table 1). They were sown in flat trays filled with a standard peat mixture substrate for
germination (C200) from Stender AG, Germany. Substrate contains 0.5 g/l NPK fertiliser and
had an electrical conductivity of 0.25 and pH 5.0-6.0 (CaCl2 ). 15 days after sowing (DAS),
the seedlings were transplanted into 9 cm containers filled with standard peat mixture
substrate (B700) from the same company. Substrate contains 1g/l NPK fertiliser and had an
electrical conductivity of 0.53 and pH 5.8 (CaCl2 ).
Table 1: Tomato cultivars used in this experiment

Cultivars Heat susceptibility Company

UC 82-B Less heat tolerant Peto seed company, USA
Drd85 F1 Heat tolerant De Ruiter Seeds, the Netherland
Kervic F1 Heat tolerant De Ruiter Seeds, the Netherland

The transplants were grown in the greenhouse of the Department of Vegetable Crops, Institute
for Horticultural Sciences, Faculty of Agriculture and Horticulture, Humboldt-Universität zu
Berlin (Latitude 52° 30` N, Longitude 13° 25` E). Tomato plants were watered daily. Twice a
week 40 ml of 0.2% soluble liquid fertiliser (12N-4P-6K) were applied to each pot. Tomato
transplants were transplanted at 30 DAS into 14 cm diameter pots filled with same substrate.
35 DAS the transplants were subjected to heat shock treatments by immersing the shoot
system in a hot-water bath at 50 °C for 30 s. Another set from each cultivar was left as control
(without heat shock treatment). Afterwards the plants were divided into two sets, one set was
transferred in one plant growth chamber under normal temperature (NT), 26/20 °C (day/night)
for 13/11 h (light/dark). Another set was transferred in a second plant growth chamber under
HS condition, 37/27 °C (day/night) temperatures, 13/11 h (light/dark). On the day a 550 µE
m-2 s-1 irradiance from a combination of fluorescent and incandescent lights were provided for
each set. Completely randomised design was followed for trial. Experiment was conducted
twice: with Kervic F1 , Drd85 F1 and UC 82-B in first experiment and with UC 82-B and
Drd85 F1 in a second one. Here only the results of the first experiment were presented.

The following parameters were recorded:

Plant height (cm) from substrate surface to the vegetative point, leaf area (cm2 ) with an
electronic leaf area, type Li-3100 (Licor, NE-USA), number of flowers per plant, leaf fresh
and dry weight (g plant-1 ) as well as stem fresh and dry weight (g plant-1 ).
Number of pollen grains per field was determined as follows: flowers samples at anthesis
were taken from the first four inflorescence twice a week for each cultivar. Each flower at the
stage of anthesis was collected into a 2 ml microtube and homogenised after adding 200 µl of
germinating solution according to Aloni et al. (2001). Drops of the solution with the released
pollen grains were mounted on hemocytometer slide and counted with a light microscope 70x
per field according to Peet and Bartholemew (1996) and Sato et al. (2000).

Data analysis
Collected data were analysed using the statistical software SPSS version 9.0. One-way
analysis of variance (ANOVA) was used to determine differences among treatments. Mean
separation was done by Tukey test. In tables and figures, means with same letters indicate no
significant differences between treatments.

Results

There were systematic and consistent differences between the plants that subjected and not
subjected to heat shock treatment at both temperature regimes. The results of the present study
indicated that there was no positive effect of heat shock treatment on tomato plants under both
temperatures regimes.
Plant height was generally reduced for the plants that subjected to heat shock treatment
compared to that not subjected to heat shock treatment. At both temperature regimes, there
were significant differences among the cultivars when subjected or no subjected to heat shock
treatment. Kervic F1 and Drd85 F1 had the highest and UC 82-B the lower plant height.
Similar results were obtained for stem-fresh and dry weight (Table 2). Among the cultivars,
Kervic F1 and Drd85 F1 had the larger stem fresh weight at both temperature regimes.

Generally, larger leaf-fresh and dry weight were found by plants that not subjected to heat
shock treatment compared to that subjected to heat shock treatment at both temperature
regimes (Table 2). Similar results were found for leaf area. Plants not subjected to heat shock
treatment had tendency higher leaf area compared to that subjected to heat shock treatment at
both temperatures regimes. Among cultivars there were no significant differences when plants
subjected to heat shock treatment at both temperature regimes (Fig. 1).

37/27 °C
1700
A
1500
a
1300 ABCD ABCD
BCD
CD
2

1100 D
areacm

bcdef cdef
900 def ef
f
Leaf

700

500

300

100
Kervic F1 con Drd 85 F1 con UC 82-B con Kervic F1 Drd 85 F1 UC 82-B

Fig. 1: Effect of heat shock and heat stress on leaf area (cm2 ).
Differences between bars labeled by the same letter are not significant (P<0.05).
(con. = control, without heat shock treatment)

37/27 °C

70 A

60 BCD
C
Number of pollen grains per field

D
50
EF
F
40

30

20

abc a
10 abc abc bc c

0
Kervic F1 con Drd 85 F1 con UC 82-B con Kervic F1 Drd 85 F1 UC 82-B

Fig. 2: Effect of heat shock and heat stress on number of pollen grains per microscopic
field.
Differences between bars labeled by the same letter are not significant (P< 0.05)
(con. = control, without heat shock treatment)
Fig. 2 shows the number of pollen grains per microscopic field. Number of pollen grains
produced and released by the plants under NT conditions were always higher than those
produced and released under HS conditions. Among the cultivars at HS conditions there were
no significant differences when the plants were not subjected to heat shock treatment.
Drd85 F1 had the highest numbers of pollen grains when the plants were subjected to heat
shock treatment. At NT there were significant differences when not subjected to heat shock
treatment, while UC 82-B have with approx. 39 pollen grains per microscopic field the lower
one.

Discussion

High temperature condition strongly affected the vegetative and reproductive organs and
tissues of tomato plants for all cultivars. For the most of vegetative parameters the most
affected cultivar was UC 82-B. Kervic F1 and Drd85 F1 were more tolerant to high
temperatures than UC 82-B.

This confirms earlier findings of Abdalla and Verkerk (1968), Abdul-Baki (1991), Peet et al.
(1997) and El Ahamdi and Stevens (1979) and, that revealed the adverse effect of HS on the
vegetative and reproductive development in tomato plants.

The effect of HS was more pronounced in the reproductive as in vegetative development

(compare the result of Fig. 2 with the results of Fig. 1 and Table 2). Kuo et al. (1986) suggest
as mechanism proline accumulation in tomato leaf tissue at high temperature. Proline thus
causes the depletion of proline in the reproductive tissue, thereby seriously reducing pollen
formation or viability.
In our study pollen production was reduced in all cultivars at HS conditions. However, Kervic
F1 and Drd85 F1 seem to be tolerant to HS conditions and produced a higher number of
pollen grains than the less heat tolerant one, UC 82-B.

Yarwood (1961) and Lin et al. (1984) reported positive effects of heat shock treatments on the
plants that later on expose for a short period of time to higher temperature. Heat shock
treatment in the present study have no positive effect on the vegetative and reproductive
development and the hope that heat shock treatment would be beneficial for tomato plants,
particularly for the reproductive development at high temperatures was not fulfilled. This is in
agreement with Abdul-baki (1991) who observed and suggested that heat shock proteins have
a little to do with reproductive stage. Also the plants in our experiments were well irrigated.
Kimpel and Key (1985) reported that HSPs in soybean might accumulate under hot field
conditions for drought plants but not for irrigated plants.

Under field conditions in Sudan other factors, such as low relative humidity, insect and virus
diseases as well as soil physical properties have also to be considered. Optimization of
microclimate could be very important to ensure a good performance of new tolerant varieties
cultivated in summer periods in Sudan.

Acknowledgments
The “Deutscher Akademischer Austauschdienst” (DAAD) is acknowledged for providing the
financial support for the first author. The Peto Seed Company, USA and De Ruiter Seed
Company, the Netherland are acknowledged for providing tomato seeds.
References

Abdul-Baki, A. A. (1991). Tolerance of tomato cultivars and selected germplasm to heat

stress. J. Amer. Soc. Hort. Sci. 116(6): 1113-1116.
Abdalla, A. A. and Verkerk, K. (1968). Growth, flowering and fruit set of the tomato at high
temperature. Neth. J. Agr. Sci. 16: 71-76.
Aloni, B., Peet, M.M., Pharr, M., and Karni, L. (2001). The effect of high temperature and
high atmospheric co2 on carbohydrate changes in bell pepper (Capsicum annum) pollen in
relation to ist germination. Physiologia Plantarum 112:505-212.
Chen, H.H., Shen, Z-Y. and Li, P.H. (1982). Adaptability of crop plants to high temperature
stress. Crop Sci. 22:719-725.
Dinar, M., and Rudich, J. (1985). Effect of heat stress on assimilate partition in tomato. Ann.
Bot. 56:239-249.
El Ahamdi, A. B. and Stevens, M. A. (1979). Reproductive responses of heat-tolerant
tomatoes to high temperatures. J. Amer. Soc. Hort. Sci. 104(5): 686-691.
Jahn, M., Nega, E., Werner, S. (2000). Pilzbefall an gemüsesaatgut: Verträglichkeit und
Wirkung der Heißwasserbehandlung. Gemüse 3: 17-19.
Kuo, C.G., Chen, H. M., and Ma, L.H. (1986). Effect of high temperature on proline
temperature content in tomato floral buds and leaves. J. Amer. Hort. Sci. 111(5): 746-750.
Kimpel, J.A., and Key, J.L. (1985). Presence of heat shock mRNA as in field grown
soybeans. Plant Physiol. 79:672-678.
Lin, C., Robert, J.K., and Key, J.L. (1984). Acquisition of thermotolerance in soybean
seedlings. Synthesis and accumulation of heat shock proteins and their cellular
localization. Plant Physiol. 79:672-678.
Loaiza-Velarde, J.G., and Salveit, M. E. (2001). Heat shocks applied either before or after
wounding reduce browning of lettuce leaf tissue. J. Amer. Soc. Hort. Sci. 126(2): 227-
234.
Loaiza-Velarde, J.G., Tomas-Barbera, F.A. and Salveit, M. E. (2001). Heat shocks applied
either before or after wounding reduce browning of lettuce leaf tissue. J. Amer. Soc. Hort.
Sci. 122(6): 873-877.
Peet, M.M., and Batholemew, M. (1996). Effect of night temperature on pollen
characteristics, growth, and fruit set in tomato. J. Amer. Soc. Hort. Sci. 121 (3): 414-519.
Peet, M.M., Willits, D. H., and Gardner, R. (1997). Response of ovule development and post-
pollen production processes in male-sterile tomatoes to chronic, sub-acute high
temperature stress. J. Experimental Botany. 48 (306): 101-111.
Rick, C.M., and Dempsey, W.H. (1969). Position of the stigma in relation to fruit setting in
the tomato. Bot. Gaz. (Chicago) 130:180-186.
Sato, S., Peet, M.M., and Thomas, J.F. (2000). Physiological factors limit fruit set of tomato
(Lycopersicon esculentum Mill.) under chronic, mild heat stress. Plant, Cell and
Environment. 23:719-726.
Vierling, E. (1991). The roles of heat shock proteins in plants. Annu. Rev. Plant Physiology
Plant Mol. Biol. 42:579-620.
Yarwood, C. E. (1961). Acquired tolerance of leaves to heat. Science 134:941-942.
Table 2: Effect of heat shock and heat stress on some plant parameters.

Parameters Plant height Stem fresh weight Stem dry weight Leaf fresh weight Leaf dry weight
(cm) (g plant-1 ) (g plant-1 ) (g plant-1 ) (g plant-1 )
Treatments 37/27 °C 26/20 °C 37/27 °C 26/20 °C 37/27 °C 26/20 °C 37/27 °C 26/20 °C 37/27 °C 26/20 °C

Kervic F 1 con. 69.3 a* 65.7 b 31.93 abc 36.18 a 4.31 abc 4.79 a 58.92 bcdef 62.64 a 10.18a 8.40 a

Drd 85 F 1 con. 64.7 ab 78.0 a 35.05 a 31.10 abc 5.15 a 4.53 a 58.59 cdef 50.29 ef 9.94a 7.70 ab

UC 82-B con. 49.7 cd 37.7 cd 24.09 de 24.09 de 3.66 cd 2.33 cd 83.27 a 51.96 bcdef 10.86a 7.38 ab

Kervic F1 66.7 a 66.0 ab 30.24 bc 25.99 cd 4.26 abcd 3.20 bcd 57.79 def 50.50 def 9.92a 5.85 b

Drd 85 F1 57.7 bc 77.7 ab 27.68 cd 30.49 bc 3.92 bcd 4.04 ab 42.33 f 46.89 f 8.09b 7.00 ab

UC 82-B 42.0 d 36.3 d 20.40 e 20.40 e 3.27 d 2.28 d 55.05 ef 51.50 cdef 10.12a 7.36 ab

*Means with same letters in the columns are not significantly different (P<0.05).
(con. = control, without heat shock)