Liming WU, Xichun ZHANG, Guanghui XIAO

College of Plant Science Technology, Beijing University of Agriculture / Beijing Key Laboratory of New Technology in Agricultural Application, Beijing 102206, China

Tomato is a warm-season vegetable crop. Temperature has complex influence on plants by changing various environmental factors such as light, CO2and soil moisture in greenhouse. At present, numerous studies abroad have proven that single environmental factors such as light,temperature and soil moisture have certain effects on the growth and photosynthetic characteristics of plants[1-9],but the joint action of several environmental factors on plant growth has rarely been reported. Zou[10]found that the daily variation of tomato leaf photosynthetic rate was a result of light, temperature, humidity and other environmental factors. Zhao et al.[11]believed that a short-term exposure to sub-high temperature accelerated tomato plant growth while a long-term exposure to sub-high temperature led to prematurity finally. Light mainly affects photosynthesis of tomato,as low light reduces its photosynthetic rate and yield. The study of Liu et al.[12]showed that appropriate shading at noondays of later flowering period significantly improved photosynthesis and tomato yield.The study of Chen et al.[13]showed that the leaf area and plant height of peppers increased in response to weakened light. In addition, soil moisture has different influences on stem and leaf area of tomato seedlings. Zhang et al.[14]found that a low soil moisture content at seedling stage increased cucumber yield while a higher soil moisture content led to leggy seedlings and reduced production. The study of Liu et al.[15]showed that irrigation deficit at different stages reduced tomato production by various extents, while the reduction was smallest by water deficit at fruit enlargement stage. All above studies proved that growth and development of tomatoes were influenced by vari-ous extents under different conditions.Therefore,in the present study,biological traits of three tomato cultivars grown under different environmental conditions were measured and compared to investigate their adaptability to environmental conditions and to determine the environmental factors influencing tomato growth and development. And the results will provide references for the control of temperature, light and soil water in tomato cultivation.

Materials and Methods

Materials

Three tomato cultivars Jiayuanfenwang 105,Hongbaoshi and Mengdalisi were selected as the experimental materials.

Methods

The field trials were carried out in the greenhouse of the experimental base of Beijing University of Agriculture in 2009, and the laboratory tests were conducted in the key laboratory of College of Plant Science Technology, Beijing University of Agriculture.

Thirty-six plants of each tomato cultivar were divided into three groups grown under different conditions: normal, shading and drought. The plants grown under normal condition was considered as the control. The ratio of light intensity in shading treatment and control was set as 2.75 ∶1 in sunny days and 3.15 ∶1 in cloudy days. For drought treatment, water supply was reduced to 70% of that in control. The plants were measured every week for plant height, stem diameter, plant expansion, single-tomato weight, leaf shape index,fruit diameter and chlorophyll content.

Table 1 Biological traits of tomato

Measurement of plant height and plant expansion Five plants were selected and measured using a tape for plant height and plant expansion at maturity stage. And the averages for each treatment were calculated.

Measurement of leaf shape index

Five well-grown and pest-free plants were selected from each treatment for the measurement of leaf shape index.The leaf length (cm) and width (cm) of the representative large leaves of these plants were measured using a set square and averaged. Finally, leaf shape index of each treatment was calculate according to the formula as follows:

Leaf shape index = Leaf length(cm)/Leaf width(cm)

Determination of growth type

Tomatoes were classified into two different growth types:indeterminate and determinate.The indeterminate growth types kept growing upward, and were characterized by long internode and tall plants. And most of the indeterminate growth types grew their first inflorescence at the 7thto 9thnodes and then one inflorescence every three leaves. Their terminal buds continued to grow till frost date. The determinate growth types had smaller plants, short internode, stout stems, dense clumps,2-4 inflorescences on the main stem and one inflorescence on the top end.When the top inflorescence formed the main stem stopped growing upward.

Measurement of tomato fruit traits Ten ripe tomatoes were selected from each treatment and were measured for their weight, size, color and flavor.The weight of 10 tomatoes from every treatment was measured using an electronic balance(0.01-2 200 g)and then divided by 10 to obtain the average weight of a tomato. Tomato color was characterized by green, yellow,pink, red, orange red, bright red and purple etc. by comparing with that of fully ripe tomatoes. Tomato flavor was classified as sour, sour sweet, sweet sour, slight sweet and sweet by comparing with that of fully ripe tomatoes.

Measurement of chlorophyll content

Wherein,C is the concentration of chlorophyll (mg/L); V refers to the volume of the extract (ml); A stands for the area or fresh weight of the leaf (g or dm2).

Statistical analysis The raw data were standardized or normalized before analyzed by Excel. Analysis of variance was performed with DPS.

Results and Analysis

Effects of environmental factors on biological traits of tomato

As shown in Table 1, singletomato weight, leaf shape index and plant height were more affected by environmental factors while other biological traits were little affected. Singletomato weight of the three cultivars from large to small among the three treatments was control＞drought treatment ＞shading treatment. The leaf shape index from large to small was among the three treatments control ＞shading treatment ＞drought treatment for Jiayuanfenwang 105, control ＞drought treatment ＞shading treatment for Mengdalisi, shading treatment ＞control ＞drought treatment for Hongbaoshi.Plant height from large to smallamong the three treatments was shading treatment ＞control ＞drought treatment for both Jiayuanfenwang 105 and Hongbaoshi,and control＞drought treatment ＞ shading treatment for Mengdalisi.

Effects of environmental factors on plant growth speed of tomato

As shown in Fig.1, the plant height increase of Jiayuanfenwang 105 changed with the variation of temperature in all the three treatments.From the 7thto the 14thd of growth period with temperature at 20-25 ℃, its plant height increase in all the three treatments gradually increased, in a descending order of shading treatment ＞control ＞drought treatment.From the 14thto the 21std with temperature at 25-30 ℃, the plant height increase in all the three treatments declined, in a descending order of shading treatment ＞ control ＞ drought treatment.From the 21stto the 28thd of growth period with temperature at 30-35 ℃, plant height increase these treatments declined, in a descending order of shading treatment ＞drought treatment ＞control. From the 28thto 35thd of growth period with temperature dropping from 35 to 30 ℃, plant height increase in both shading treatment and control increased while that in drought treatment declined. On the 35thd of growth period,the plant height increase in the three treatments in a descending order was shading treatment ＞control ＞drought treatment.From the 35thto the 42ndd of growth period with temperature dropping from 30 to 25 ℃, the plant height increase increased again,in a descending order of shading treatment ＞ control ＞drought treatment.

As shown in Fig.2, the plant height increase of Hongbaoshi changed with the variation of temperature in all the three treatments. From the 7thto the 14thd of growth period with temperature at 20-30 ℃,its plant height increase in all the three treatments increased, in a descending order of shading treatment ＞control ＞drought treatment.From the 14thto 21std of growth period with temperature at 25-30 ℃, the plant height increase in all the three treatments increased slightly,in a descending order of shading treatment＞control ＞drought treatment. From the 21stto 28thd of growth period with temperature at 30-35 ℃,its plant height increase in all the three treatments declined in a descending order of control ＞shading treatment ＞drought treatment.From the 28thto the 35thd of growth period with temperature dropping from 35 to 30 ℃, the plant height increase in all the three treatments declined in a descending order of drought treatment ＞shading treatment ＞control. From the 35thto 42ndd of growth period with temperature dropping from 30 to 25 ℃, the plant height increase in all the three treatments increased again, in a descending order of shading treatment ＞control ＞drought treatment.

As could be seen from Fig.3, the plant height increase of Mengdalisi also changed with the variation of temperature in the three treatments. From the 7thto the 14thd of growth period with temperature at 20-25 ℃,its plant height increase in all the three treatments increased, in a descending order of control ＞drought treatment ＞shading treatment.From the 14thto 21std of growth period with temperature at 25-30 ℃, its plant height increase in all the three treatments declined slightly,in a descending order of control ＞shading treatment＞drought treatment.From the 21stto the 28thd of growth period with temperature at 30-35 ℃,the plant height increase of Mengdalisi in all the three treatments increased,ina descending order of drought treatment＞ control ＞ shading treatment.From the 28thto the 35thd of growth period with the temperature dropping from 35 to 30 ℃, the plant height increase of Mengdalisi in all the three treatments declined, in a descending order of drought treatment ＞shading treatment ＞control. From the 35thto 42ndd of growth period with temperature dropping from 30 to 25 ℃, the plant height increase in all the three treatments increased again, in a descending order of shading treatment ＞control ＞drought treatment.

In summary, the tomato plants of Jiayuanfenwang 105 in shading treatment grew faster than those in the other two treatments throughout its growth period. Among the three treatments of tomato cultivar Hongbaoshi,the plants in shading treatment grew fastest at early growth period (with temperature at 20-30 ℃),the plants of control group grew fastest at middle growth period (with temperature at 30-35 ℃), and the plants in drought treatment grew fastest at late growth period (with temperature dropping from 35 to 30 ℃). Among the three treatments of tomato cultivar Mengdalisi,the plants in control grew fastest at early growth period (with temperature at 20-30 ℃), the plants in drought treatment grew fastest at middle growth period(with temperature at 30-35 ℃),and the plants in drought treatment grew fastest at late growth period(with temperature dropping from 35 to 30 ℃).

Effects of environmental factors on fruit growth speed

As shown in Fig.4,the fruit diameter increase of Jiayuanfenwang 105 changed with the variation of temperature in the three treatments. On the 7thd of growth period with temperature at 25 ℃,the fruit diameter increase of Jiayuanfenwang 105 in all the three treatments was in a descending order as shading treatment ＞ control ＞drought treatment. On the 14thd of growth period with temperature at 30℃, the fruit diameter increase of Jiayuanfenwang 105 in the three treatments was in a descending order of control ＞drought treatment ＞shading treatment.On the 21std of growth period with temperature at 35 ℃, its fruit diameter increase in the three treatments in a descending order was control ＞ shading treatment ＞ drought treatment.On the 28thd of growth period with temperature at 30 ℃, its fruit diameter increase in the three treatments in a descending order was shading treatment ＞control ＞drought treatment.

The fruit diameter increase of Hongbaoshi changed with the variation of temperature in the three treatments.As shown in Fig.5, on the 7thd of growth period with temperature at 25℃,the fruit diameter increase of Hongbaoshi in the three treatments in a descending order was control ＞shading treatment＞drought treatment. On the 14thd of growth period with temperature at 30 ℃,its fruit diameter increase in the three treatments in a descending order was control ＞drought treatment＞shading treatment. On the 21std of growth period with temperature at 35℃, its fruit diameter increase in the three treatments in a descending order was control ＞ shading treatment ＞drought treatment. On the 28thd of growth period with temperature at 30℃, its fruit diameter increase in the three treatments in a descending order was drought treatment ＞shading treatment＞control.

The fruit diameter increase of Mengdalisi changed with the variation of temperature in the three treatments.As shown in Fig.6, on the 7th d of growth period with temperature at 25℃,the fruit diameter increase of Mengdalisi in the three treatments in a descending order was shading treatment＞control ＞drought treatment.On the 14thd of growth period with temperature at 30 ℃, its fruit diameter increase in the three treatments in a descending order was control ＞drought treatment ＞shading treatment. On the 21std of growth period with temperature at 35 ℃,its fruit diameter increase in the three treatments was shading treatment＞drought treatment ＞control.On the 28thd of growth period with temperature at 30 ℃, its fruit diameter increase in the three treatments was shading treatment ＞control ＞drought treatment.

To sum up, among the three treatments of tomato cultivar Jiayuanfenwang 105, the fruits in shading treatment grew fastest at early growth period(with temperature at 25-30 ℃),the fruits of control group grew fastest at middle growth period (with temperature at 30 -35 ℃), and its fruits in shading treatment grew fastest at late growth period (with temperature dropping from 35 to 30 ℃). Among the three treatments of tomato cultivar Hongbaoshi,the fruits of control group grew fastest at early and middle growth periods (with temperature at 25-35 ℃), the fruits of drought treatment grew fastest at late growth period(with temperature dropping from 35 to 30 ℃). Among the three treatments of tomato cultivar Mengdalisi,the fruits in shading treatment grew fastest at early growth period(with temperature at 25-30 ℃); at middle growth period thefruits of control grew fastest when the temperature was 30 ℃, and the fruits in shading treatment grew fastest when the temperature was 35 ℃; and the fruits in shading treatment grew fastest at late growth period(with temperature dropping from 35 to 30 ℃).

Table 2 Chlorophyll content of tomato

Effects of environmental factors on chlorophyll content of tomato

It could be concluded from Table 2 that the chlorophyll content of the three tomato cultivars differed slightly,it was Hongbaoshi ＞Mengdalisi ＞Jiayuanfenwang 105. Among the three treatments of all the tomato cultivars,chlorophyll content of control was the highest and that in drought treatment was the lowest.

Conclusions

Effects of temperature, low light(35% shading) and drought (70%soil moisture) on tomato plant growth

Fig.1-Fig.3 revealed that Jiayuanfenwang 105 had tolerance to low light. Treatment with 35% shading density and sufficient water supply improved tomato plant growth during its entire growth period with the temperature ranging from 20 to 35 ℃. For tomato cultivar Hongbaoshi, treatment with 35% shading density accelerated plant growth at its early growth stage;during its middle growth stage, plants grew better under the conditions of high temperature, sufficient light and water; at its late growth stage plants grew better with 70% soil moisture.The results revealed that Hongbaoshi had certain tolerance to high temperature. Mengdalisi was tolerant to drought. It grew better under the conditions of appropriate temperature,sufficient light and soil moisture at early growth stage; 70% soil moisture improved plant growth of Mengdalisi at both middle growth stage with high temperature and late growth stage.

Effects of temperature, low light(35% shading) and drought (70%soil moisture) on tomato fruit growth

Our results revealed that the fruits of Jiayuanfenwang 105 grew better with 35% shading density at its early and late growth stages, and they grew better with sufficient light and water at its middle growth stage under high temperature stress. The fruits of Hongbaoshi grew better under the conditions of sufficient water and light at early and middle growth stages,and they grew better with 70% soil moisture at late growth stage when temperature dropped. For Mengdalisi,treatment with 35% shading density improved fruit development at early and late growth stages; at middle growth stage the fruits grew better with sufficient water and light at temperature of 30 ℃,and 35%shading density at temperature of 35 ℃.

Discussion

Temperature

Zhang et al.[16]believed that 33-35 ℃was the upper limit of the optimum temperature range for tomato growth and development and its growth could be seriously affected by temperature over 35 ℃. Zhao et al.[11]found that that a short-term temperature increase by 8-10 ℃ (without exceeding 35 ℃)promoted plant growth,but a long-term exposure to high temperature inhibited plant growth; and high temperature could shorten crop growth period[17-18].Our results basically agreed well with previous studies:the tomatoes grew fastest at temperature ranging from 20 to 30 ℃,and fruit yield maximized at temperature ranging from 25 to 30 ℃. The growth and development of the three tomato cultivars varied under high temperature ranging from 30 to 35 ℃.Among the three cultivars,only the plant growth of Hongbaoshi was promoted under high temperature stress with sufficient light and water at middle stage, suggesting that Hongbaoshi was tolerance to high temperature. High temperature could not improve the plant growth of Jiayuanfenwang 105 and Mengdalisi only if it combined with low light or drought. The results revealed temperature together with other environmental factors could regulate plant growth and development.

Light

Our results revealed that treatment with 35% shading density improved the plant growth and development of Jiayuanfenwang 105, and the fruit growth of Mengdalisi at 35 ℃,which were consistent with the results of Liu et al.[12-13]. The study of Yang et al.[19]reducing natural light intensity to 75%had no significant effect on tomato plant growth and fruit yield, but the tomato plant biomass, dry matter accumulation and yield significantly decreased when the light intensity continued to decline, which were not consistent with our results. The reason may be that plants have different adoptability to environment.

Soil moisture

Kong et al.[20]found that 80% soil moisture content was optimum to tomato growth. However, our results revealed that 70% soil moisture content improved the plant growth of Mengdalisi, which proved its tolerance to drought. Such a result agreed well with the studies of Zhang et al.[14-15].Previous studies also showed that fruits under water stress had better quality than those under normal irrigation condition. The reduced soil moisture from the 28th-35thd of growth period with temperature at 35 ℃promoted the plant growth of Mengdalisi. In addition,soil moisture had greater impact on the synthesis of chlorophyll than light. The reduced light and soil moisture also led to the decline of chlorophyll content, which was likely aresult of temperature, light and soil moisture.

The yield and quality of tomato are a synergistic result of various environmental factors. Therefore, lots of factors should be considered for the regulation of tomato growth, and tomato yield and quality will be improved by regulating light, temperature, soil moisture and other environmental factors with artificial means and breeding of new tomato cultivars tolerant to drought and light.

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