CC BY
13Sherzod Rajametov12, Sam-Seok Kang2 and Karim Baymetov3*
^National Agrobiodiversity Center, NAAS, RDA, Suwon, 441-853, Republic of Korea
2 Pear Research Station, NHRI, RDA, Naju 520-821, Korea 3Uzbek Research Institute of Plant Industry, UzSPCA, Tashkent 111202, Uzbekistan Corresponding author (E-mail: baymetov40@mail.ru, Tel: +99871-260-11-69
CHANGING OF THE WATER REGIME, LEAF ANATOMICAL STRUCTURE, CHLOROPHYLL COMPOSITION AND ELECTROLYTE LEAKAGE IN DIFFERENT PEAR CULTIVARS DURING SUMMER PERIOD UNDER NATURAL HUMIDITY CONDITION OF KOREA
(Изменение водного режима, анатомического строения листа, состава хлорофилла и утечки электролита в разных сортах груш в летний период в условиях естественной влажности Кореи)
Running Title: Water Regime and Morpho-Physiological Process in Different Pear Cultivars
ABSTRACT
The present study was conducted to evaluate the dynamics of the water regime in association with morpho-physiological activity in the different pear cultivars during the summer of 2013, such as: water content in leaves (WCL) and annual shoots (WCS), water deficit in leaves (WDL) and annual shoots (WDS), electrolytic leakage (EC), leaf anatomical structure and stomata parameters, total chlorophyll content. There were revealed some pattern in water regime so, regardless of the climatic condition WCL, WCS in all cultivars was decreased from early June to late August, however, WDL and WDS were differed significantly in comparison with WCL and WCS, where WDL seasonally fluctuated in all cultivars except Bartlett, which distinguished with high stable rate and there is an imbalance between WDL and WDS. According to results was not found the significant relationship between water regime and EC, stomata parameters, the anatomical structure and total chlorophyll content of the leaves in the summer period, whereas there RH of air and soil condition was sufficiently moistened which might be protected to show real ability of cultivars.
Therefore, pear cultivars cannot show their real ability in water regime and physiology especially under humid condition, and cannot be detected of resistance to stress factor and some patterns which are manifested in the dry season or in special controlled condition experience.
Keywords: water content, chlorophyll content, electrolyte conductivity, epidermis, stomata pore, mesophyll.
В данном исследовании была проведена оценка динамики водного режима в связи с морфофизиологиче-ской активностью в различных сортах груши в течение лета 2013 года, были изучены такие показатели, как: содержание воды в листьях и однолетних побегах, дефицит воды в листьях и однолетних побегах, электролитическая утечка, анатомическая структура листа и параметры устьиц, общее содержание хлорофилла. Были выявлены некоторые тенденции в водном режиме: так, независимо от климатических условий содержание воды в листьях и однолетних побегах во всех сортах груш было уменьшено с начала июня до конца августа, однако дефицит воды в листьях и однолетних побегах существенно отличался по сравнению с содержанием воды в листьях и однолетних побегах. При этом дефицит воды в листьях сезонно колебался во всех сортах, кроме сорта Бартлетт, который отличался высокой стабильностью и дисбалансом между дефицитом воды в листьях и однолетних побегах. По результатам исследований не было найдено значимой взаимосвязи между водным режимом и электролитической утечкой, параметров устьиц, анатомического строения и общего содержания хлорофилла в листьях в летний период, поскольку воздух и почва были достаточно увлажненными. Это могло несколько искажать реальную способность сортов груш к изменению водного режима.
В связи с этим сорта груш не смогли показать свою реальную способность в водном режиме и физиологии в условиях влажного климата, также не может быть подтверждена устойчивость сортов груш к стресс-факторам и некоторые закономерности, которые проявляются в сухой сезон или в специальных условиях, регулируемых проводимым экспериментом.
Ключевые слова: содержание воды, содержание хлорофилла, проводимость электролита, эпидермис, устьица, мезофилл.
Introduction
Water availability is one of the major factors that effect on plant productivity. The necessity regulation of this factor, particularly through irrigation, is primarily concerned with the actual need of plants in water, and to investigate the characteristics of their water regime (Peti-nov, 1962, Kushnirenko, 1964). The water content in the tissues of fruit plants depends on the growing conditions,
as well as associated with the age changes in organ and whole organism and shortage of water in the plant is significantly effect on morpho-physiological properties of the plant organs (Bahanova, 2003; Rajametov et al., 2010, Zayseva, 2011). Water regime of leaves is an underlying factor to determine physiological state of the trees, as in drought years when falling relative humidity reduces the activity of the root system, and against this background
that marked inhibition of growth of leaves and shoots (Trunov, 2005; Ulyanovskaya et al., 2005).
Plants usually respond to their changing environment in a complex, integrated way allowing them to respond and adapt to the specific set of conditions and constraints present at a particular time. It involves an array of physiological and biochemical modifications in plants including leaf wilting, reduction in leaf area and stomata, leaf abscission, stimulation of root growth, changes in relative water content, electrolytic leakage, generation of reactive oxygen species, and accumulation of free radicals which disrupt cellular homeostasis by reacting with lipids, proteins, pigments, and nucleic acids resulting in lipid peroxidation, membrane damage, and the inactivation of enzymes, thus affecting cell viability (Bajji, et al., 2001; Bahanova, 2003; Bartels and Sunkar, 2005; Zakharchuk and Ryazanova, 2013). Molecular responses to abiotic stresses, on the other hand, include stress perception, signal transduction to cellular components, gene expression, and, finally, metabolic changes imparting stress tolerance (Agarwal et al., 2006, Lata and Prasad, 2011). The genes thus induced by stress not only function in protecting cells from stress by the production of important metabolic proteins but also in regulating the downstream genes for signal transduction (Ingram and Bartels, 1996; Bray, 1997; Shinozaki and Yamaguchi-Shinozaki, 1997, Nakashima1 et al., 2000; Bohnert et al. 2001).
Also, chlorophyll and stomata is vital for photosynthesis, gas exchange and respiration and so on, which plays very important role in plants physiology (Trejo et al., 1991, 1993; Rotondi and Predieri, 2002; Pruzinska et al., 2007). In whole on the water balance and physiological properties of plants are passed under influence many factors and in literature are presented limit information about tendency of water potential and physicochemical composition of pear organs during summer period, and many researchers are concentrated they investigation only in certain period and under special treatments. Therefore in this paper we presented research work on water regime in leaves and annual shoots in association with leaves anatomical parameters, total chlorophyll content and electrolyte conductivity of leaves is held during vegetation period in natural condition of Republic Korea.
Materials and the methods
Experiment was carried out in Naju Pear research station (RDA) during the summer of 2013 year and used different originated pear cultivars Bartlett (USA), Nash-vati iz Pishkarina (UZB), Niitaka (JAP) and Chuwhang-bae (KOR). It should be noted that all cultivars originated under humid area except Nashvati iz Pishkarina which genealogic was formatted in the dry area. All experiments were not subjected to a special treatment and conducted under natural conditions. The main purposes were to study of the occurring physiological features such as: changing water regime, electrical conductivity, total leaf chlorophyll content etc. Water regime in the leaves and shoots studied afternoon at 0300PM from the annual shoot with leaves from position between 30 and 70 cm, where each shoot was about 0.80-1.0 m with length and diameter 0.7-1.0 mm.
Water contents was estimated as a percentage of its total content in annual shoots and leaves and calculated by the formula:
WC%=(W1 - W2) x 100/W 1, where WC%-water content, Wi-initial mass of shoots or leaves, W2 - dry mass of shoots or leaves.
Water deficit in the shoots and leaves is determined as a percentage of its total content a state of complete saturation (shoots and leaves should be kept in water 24 hour) and are expressed as:
WD% = (WAx100)/W, where WD- water deficit, WA- water absorbed at saturation of the shoots and leaves, which is determined by the difference of mass of shoots and leaves before and after complete saturation, W- presence of water, the difference between the mass of shoots and leaves after complete saturation with water and dry mass of sample.
Electrical conductivity (EC) was measured afternoon at 0300PM by using an Orion conductivity TDS meter model 124 conductimeter (Orion, Germany). In order to determine of electrolyte leakage for each treatment 3 leaves from cultivar was collected, weighed and cut into segments (ca. 0.5 cm) on 5.0 gram. Segments originating from the same shoot was put into 40 ml of distillated water in a test tube and allowed to stand for 15 h in the dark at 20°C. An initial electrical conductivity measure (ECi) was taken at the beginning of this rehydration period. All tubes were heated for 30 min in water under 95°C. Then, the tubes containing the segments was returned into the dark at 20 °C and kept for 15 h. Following these readings, the total electrical conductivity (ECt) will be measured. Electrolyte leakages (%) are expressed as: (ECi/ECt) x 100.
The stomata area was determined from middle part of annual shoot leaves low part morning at 0800AM and afternoon at 03 00PM by electron microscope AXIO (Carl Zeiss, Germany, and magnification- x50-400). The leaf area (cm2) was measured in mid-August from middle part leaves of annual shoots by LI-3100 Area meter (USA) and to determine leaf anatomical structure the leaf samples were initially fixed in 2.5% glutaraldehyde for 90 min at 40 and then rinsed four or five times with 0.1M phosphate buffer (pH 7.2). The second fixing process was achieved using 1% osmium tetraoxide for 90 min and rinsed again with 0.1 M phosphate buffer five times. The fixed samples were dehydrated in the alcohol series with increasing concentrations. Dehydrated samples were laid in a silicon mold with epon + D.M.P. 30 for 4 days at 60 □. After polymerization, the embedded samples were sectioned into 1 ^m thickness using an ultramicrotome (Ultracut R. Leica Co., Austria) and observed under light microscopy AXIO (Carl Zeiss, Germany, and magnification- x200)
Total chlorophyll content was analyzed morning at 0800AM and afternoon at 0300PM by Eon Microplate Spectrophotometer USA- at 651 and 664 nm (mg/g-1 fresh weight). Leaf disks each 6.25 mm in diameter, were punched from the medium part of annual shoot leaves. The disks were placed immediately into 25 mL of 100% methanol, and pigments were allowed to be extracted in dark at 4.0°C for 14 h.
Results and discussion
South Korean environment conditions of summer are usually distinguished with warm, long sunny day and high rate of precipitation. During carry out the experiment were recorded air temperature and humidity. Dynamics of the data shows that the temperature increased from June to mid-August and reached a maximum in August about 35°C (Fig. 1). Relative humidity (RH) distinguished with consistently high during the summer especially at night time, and reached 99%, whereas the afternoon its rate was also relatively high over 50%. Monthly mean rainfall was generally higher in July and in August and total rainfall was about 700 mm during the summer and soil moisture content in all cultivars was well supplied with water, where at depth 1.0 m exceed 30-40% (data not presented).
40
35
30
25
20
Meteo condition Air humidity ► Air temperature
70
60 Ж
50
40
01.06.1316.06.1329.06.1316.07.1307.08.1321.08.13 Investigate date
Fig. 1. Climatic condition of the investigation time of 2013, Naju.
According to results the water regime in leaves and annual shoots was unstable and ranged depending on period and features of cultivars. So, regardless of the climatic condition WCL in all investigated cultivars decreased
from early June to late August where was reported (Baha-nova, 2003; Zakharchuk and Ryazanova, 2013) in fruit crops and the same pattern was detected in WCS however was detected the saving of varietal difference in this trait (Fig. 2 and 3). It should be noted that WCL in association with WCS was declining from early June to late August. Niitaka and Nashvati iz Pishkarina in comparison with cultivars Chuwhangbae and Bartlett was determined with relatively low WCL and WCS. High concentration of the water in leaves and shoots are related with physiological activity of the plant organs and absolute maximal levels characterized in the beginning of the blossom (Bahanova, 2003) and further the water content reducing due to aging of the organs but it should be noted that the cultivars which has showed high WCL in blossom cannot show high stable value during vegetation period. Gradual decline values of the water regime during the summer period associated with biological features of cultivars, by the weakening of the water availability of the plant organs which controlled by some plant regulators, hormones and genes and contribute to physiological and biochemical modifications in plants including leaf wilting, reduction in leaf area, leaf abscission, induces leaf stomata closure to reduce water loss through transpiration and decreases the photosynthetic rate in order to improve the water-use efficiency, root growth, changes in relative water content, inactivation of enzymes, thus affecting cell viability and so on (Gomez et al., 1988; Agarwal et al., 2006; Bartels and Sunkar, 2005; Lata et al., 2011 and 2011a; Zakharchuk and Ryazanova, 2014). On the basis of the above, it can be assumed that the physiological and biochemical processes in the plants are held differently and according to that water regime is different in cultivars.
Water content in leaves
75
70
ä? 65
60
55
»Bartlett »Niitaka
•Nashvati iz Pishkarina •Chuwhangbae
01.06.13 16.06.13 29.06.13 16.07.13
Investigation date
07.08.13 21.08.13
Fig. 2. Dynamic of the changing water content in leaves, 2013.
Fig. 3. Dynamic of the changing water content in annual shoots, 2013.
Water content in shoot
80 75 70
60 55
50
•Bartlett •Niitaka
•Nashvati iz Pishkarina •Chuwhangbae
t -■=--« -"
01.06.13 16.06.13 29.06.13 16.07.13 07.08.13 Investigation date
21.08.13
Water shortage is an important and integral physiological index reflecting as the degree under saturation tissue the water with insufficient water supplies, indicating the needs of plants in moisture. However, WDL and WDS were differed significantly in comparison to WCL and WCS. So, WDL seasonally fluctuated in all cultivars except Bartlett (Fig. 4), which distinguished with high stable rate. Additionally, from early June to August detected relatively high unstable values in all cultivars, where in this period in the plant organs are held a maximal intense of physiological activity with high progress of growth stage (Bahanova, 2003; Gegechkori et al., 2013.). In August regardless of high temperature WDL in Niita-ka, Chuwhangbae
WDS was detected in cultivars with common tendency decreasing from June to August (Fig. 5), and a relatively low value determined in Nahsvati iz Pishkarina. However, early June determined in all cultivars absolute minimal WDS, hereinafter increased and revealed an absolute maximal values in mid-June, further WDS rates again started to reduce, where the same pattern was detected in WCL and WCS. A minimal WDS in early June it can be assumed with high ability of uptake water by plant organs to progress of growth stage, well saturated leaves and shoots with water, temperature and humidity condition. With increasing temperature plant require-
dynamics of decreasing whereas Bartlett had reverse pattern. Almost the same pattern was determined in our experiment which was done under condition of Uzbekistan (Rajametov, 2008; Rajametov et al., 2010) where East and Central Asian pear cultivars had been distinguished with low WDL compared to European. In comparison to Korean humid condition where in June and July detected high (over 15%) and fluctuated values of WDL, there was revealed stable dynamic relatively low (about 10%) rates of the WDL during the summer in Uzbekistan, and it might be attributed to the fact that the climate is characterized by the dry without precipitation and protective mechanism are activated to saving water (Cruz et al., 2012).
ments in water will be increased until certain period. And revealed that there is an imbalance between WDL and WDS, where have difference of water absorption that related with water demand in other plant organs, age, leaf anatomical structure, xylem and roots conductivity, transpiration rates etc. (Trejo and Davies, 1991; Rotondi and Predieri, 2002; Kosma et al., 2009; Cruz et al., 2012; Aroca et al., 2012; Gegechkori et al., 2013). Especially strong shortage of water observed in all cultivars annual shoots in the mid and at the end of June and there was not found relationship between water content and water deficit of leaves and shoots.
and Nashvati iz Pishkanna showed
Fig. 4. Dynamic of the changing water deficit in leaves, 2013.
40 35 30 25 20 15 10
Water deficit in shoots
•Bartlett •Niitaka
•Nashvati iz
Pishkarina •Chuwhangbae
01.06.13 16.06.13 29.06.13 16.07.13 Investigation date
07.08.13
21.08.13
Fig. 5. Dynamic of the changing water deficit in annual shoots, 2013.
Electrolyte conductivity of leaves was distinguished with significantly differs trade in summer by assay of the water regime. Whereas, many researcher reported that electrolyte leakage measurements may be correlated with several physiological and biochemical parameters conditioning the plant responses to environmental conditions such as spectral reflectance (Garty et al. 2000; Vainola and Repo 2000), antioxidative enzyme synthesis (Liu and Huang 2000; Sreenivasulu et al. 2000), membrane acyl lipid concentrations (Lauriano et al. 2000), water use efficiency (Franca et al. 2000; Saelim and Zwiazek 2000; Bajji et al., 2001), transverse relaxation time of leaf water (Maheswary et al. 1999), stomatal resistance, osmotic potential and leaf rolling index (Premachandra et al.
1989). However, all experience was concentrated on certain time and under special treatment condition. In our case in vivo EC rates showed rising up from early June to mid-July, then when daily average temperature was significantly has increased in August and was observed sharply declining of the degree of cell membrane injury below 25% and kept point until late August (Fig. 6). Only Bartlett has relatively high level of electrolyte leakage from the cells to compare other cultivars thus provides an estimate of high tissue injury (Bandurska et al., 1997; Linden et al., 2000; Bajji et al., 2001). And in our experience was not revealed any relationship of EC between stomata parameters and with water regime of plant in summer.
Electrlyte leakage of leaves
55
45
35
25
15
•Nashvati iz Pishkarina
Chuwhangbae
01.06.13 16.06.13
29.06.13
16.07.13 07.08.13
21.08.13
Investigation date
Fig. 6. Changing of the electrolyte conductivity of leaves, during the summer 2013.
Investigation of pear leaves anatomical structure showed that the cultivars Niitaka and Chuwhangbae were distinguished with high leaf thickness, upper and lower epidermis layer, length of stomata slit between guard cells (Tab. 1) and over 1.5 times bigger diameter of the main vascular bundles especially xylem (Fig. 7) however, they had lowest density of upper and lower epidermis per 100 ^m on compare Bartlett and Nashvati iz Pishkarina. And also, in Niitaka and Chuwhangbae was detected relatively big leaf area with high weight per leaf and cm2. In com-
parison a length and density of palisade mesophyll per 100 ^m all cultivars has a negligible difference except Bartlett. According to Bahanova (2003) apple cultivars with high leaf thickness, upper and lower epidermis layer and density of stomata per mm2 contributed to increase leaf transpiration rate and low WDL, but in our case that pattern was not observed under humid Korean condition and it can be occur in the dry area.
Table 1. Analyses of the pear leaf anatomical parameters
Name Thicknessesy Length of palisade mesophyll, Width of stomata slit between guard cells, Densityy The main vascular bundlesx
Leaf, ^m Upper epidermis, ^m Lower epidermis, ^m Upper epidermis per100 ^m Lower epidermis per100 ^m Palisade mesophyll per 100 ^m Diameter, ^m Area, ^m2
Nashvati 258.7 ±2.24bz 17.24 ±1.04b 8.57 ±0.32b 115.7 ±3.30b 25.32 ±0.98c 4.9 ±0.13a 6.9 ±0.36a 11.0 ±0.28ab 181.0 ±2.18c 25750 ±622.2c
Bartlett 263.0 ±3.78b 17.34 ±0.77b 9.30 ±0.31b 128.3 ±2.11a 26.41 ±1.38bc 4.7 ±0.16a 6.3 ±0.29a 11.6 ±0.24a 162.2 ±3.07d 21250 ±714.6d
Niitaka 299.3 ±3.49a 30.07 ±1.38a 20.47 ±1.15a 117.8 ±4.30b 29.30 ±1.11ab 3.8 ±0.18b 4.7 ±0.27b 10.9 ±0.19b 308.2 ±3.04a 74690 ±1466.9a
Chuwhang 295.8 ±4.88a 26.55 ±1.65a 20.77 ±1.06a 111.4 ±4.06b 30.77 ±1.19a 3.7 ±0.16b 4.5 ±0.20b 10.9 ±0.26ab 296.4 ±4.30b 69120 ±1990.6b
yxData represented by Mean ± SD (n = 20 and 10) zMean separation within columns by LCD test, P< 0.05
Also, preliminary estimate of the leaf stomata parameters showed that depending on time of day was differed (Tab. 2). At morning time 0800 AM in comparison 03 00 PM Niitaka and Bartlett leaves stomata area was expanded significantly from 773.0 to 835.1 and 703.5 to 724.3 ^m2 respectively, whereas in Nashvati iz Pishkarina it was reduced and in Chuwhangbae was quite negligible. It might be associated with temperature and RH, xylem conductivity, needs of plant organs to uptake water, role for ABA metabolism in the regulation of stomata behavior and changes are often accompanied by closure of stomata and so on (Rodriguez and Davies, 1982; Zhang
and Davies, 1990a; Härtung and Slovik, 1991; Gollan et al., 1992; Trejo et al., 1993).
Density of stomata per mm2 was varied in cultivars from 164.8 to 214.3 pieces but in calculation on the total leaf area Niitaka and Chuwhangbae was excelled with high density, and coating stomata on total leaf surface area exceeded about 16-18%, whereas in Nashvati iz Pishkarina it was about- 11.9% respectively. And we have not found the significant relationship between water regime and the anatomical structure of the leaves in the summer period whereas there RH of air and soil condition was sufficiently moistened.
Table 2. Changes of the stomata parameters in leaf during a day
Name Stomata parameters in leaf
Density of stomatay Total covered area in leaves, % Changing of stomata area depending on timex, ^m2 length of stomatal porex, ^m2 width of stomatal porex, ^m2
08-00 AM 03-00 PM 08-00 AM 03-00 PM 08-00 AM 03-00 PM
per 2 mm per leaf (thousand)
Niitaka 214.3 ±6.7 az 14637.8 16.6 773.0 ±26.1 b 835.1 ±23.2 b 30.14 ±0.64 a 26.70 ±0.66 b 10.86 ±0.23 bc 11.42 ±0.41 b
Chuwhangbae 183.4 ±4.6 b 12972.8 17.6 961.0 ±42.0 a 968.5 ±32.2 a 31.70 ± 0.79 a 28.78 ±0.72 a 12.27 ±0.33 a 11.04 ±0.28 b
Nashvati 164.8 ±3.8 c 3064.3 11.9 761.7 ±43.5 b 720.5 ±35.0 c 23.82 ±0.77 b 25.47 ±0.79 bc 9.93 ±0.28 c 9.56 ±0.29 c
Bartlett 203.7 ±5.6 a 3523.0 14.3 703.5 ±28.5 b 724.3 ±29.1 c 25.51 ±0.77 b 24.19 ±0.62 c 11.52 ±0.56 ab 14.85 ±0.51 a
yxData represented by Mean ± SD (n = 12 and = 30) zMean separation within columns by LCD test, P< 0.05
Total chlorophyll content in all cultivars leaves regardless of the condition the minimal values were noted in Niitaka. According to Rotondi and Predieri (2002) leaves of pear cultivars Abbé Fétel and Passe Crassane was distinguished with high chlorophyll contents and they also exhibited higher photosynthetic efficiency. Some researchers (Kushnirenko and Medvedev, 1969; Bahanova, 2003) reported that the increase of the content of chlorophyll in leaves under the shortage of water is a protective response of plants and cultivars is more drought resistance. So, in our case the maximal total chlorophyll content was revealed in Nashvati iz Pishkarina and ranged depending on period of day (Fig. 8 and 9) and it may be
has high photosynthetic rates. The degree of chlorophyll in all cultivars was high at 03 00 PM in comparison morning time and reached maximum mid-July then showed reverse rate decreasing. From seasonal investigations, there was determined negative and positive correlation between total chlorophyll, and total nitrogen content in the same cultivars and data was not steady and fluctuated regardless of time investigation (data not presented).
In contrast to our results, Park et al., (2007) in apple leaves by using Portable chlorophyll meter (SPAD — 502) assayed that SPAD reading value increased from June to August but the correlation coefficients between SPAD
reading value and foliar nitrogen content tended to be gradually declined with progress of growth stage. According to Ghasemi et al., (2011) they detected positive and linear correlation between CCM-200 data, total chlorophyll, and total nitrogen content in Asian pear leaves however, that estimate was done only in June. This dis-
crepancy can be attributed to different crops, genotypes, period of experience and environments which also was determined in other crops (Blackmer and Shepers, 1995; Wu et al., 1998; Richardson et al., 2002; Rotondi and Predieri, 2002; Kowalczyk-Jusko and Koscik, 2002).
Fig. 7. Anatomical structure of the pear leaf which was originated in different condition, 2013.
1,8 1,6 1,4 1,2 1,0 0,8 0,6 0,4 0,2
Total chlorophyll content in leaves at 08-00 AM — "•Bartlett .••'^'V
•Niitaka
•Nashvati iz Pishkarina •Chuwhangbae
01.06.13
16.06.13
29.06.13
16.07.13
07.08.13
21.08.13
Investigation date
Fig. 8. Changing the total chlorophyll content in leaf at 08-00 AM during the summer 2013.
In conclusion, this experience demonstrate that the water regime, electrical conductivity, the size and density of the stomata, the total chlorophyll content of pears unstable and varies depending on the growth, age, climatic conditions. And interactions between variety and environment are very important in crop breeding in order to develop a specific variety suitable for a given region (Becker et al., 1999). Based on the presence or absence of the interaction effect, breeders may have to change the target area for cultivation or selection scheme.
In summary, the pear cultivars cannot show their real ability in water regime and physiology especially under humid condition, and to be resistant to stress factor and some patterns which are manifested in the dry season or in special controlled condition experience cannot be detected.
In order to the same cultivar can be cultivated in different habitat in the future breeders have to pay attention
to develop new cultivars on the base of the parental culti-vars which were originated under external condition, and it is necessary to conduct the study in the same format under the semiarid areas where there is no practical during the summer rains and the humidity is relatively low compared to the humid and rainy condition. In this case, it can be seen another pattern the occurring of the physiological processes whereas some cultivars which were developed in semiarid area can be characterized more resistance to compare cultivars which developed in the humid area.
Acknowledgement
This work was supported by funds of Pear research station, NHRI, RDA, Republic of Korea. The author thanks Dr. Kang, Sam-Seok and technical staff for help to do this experiment.
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Поступила в редакцию: 02.09.2014 г.
Karim Baymetov - Uzbek Research Institute of Plant Industry, UzSPCA, Tashkent 111202, Uzbekistan, e-mail: baymetov40@mail.ru, Tel: +99871-260-11-69
