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Section 8. Agricultural sciences
Muradullayev Alisher, Junior scientific worker Research Institute of Breeding, Seed Production and Agricultural Technology of Cotton Cultivation, Tashkent, Uzbekistan
Rakhmonkulov S., Academician, Research Institute of Breeding, Seed Production and Agricultural Technology of Cotton Cultivation, Tashkent, Uzbekistan
Rafiyeva F. U.,
Doctor of Philosophy (PhD), Senior researcher, Institute of Genetics and Plant Experimental Biology of the Academy of Sciences of the Republic of Uzbekistan
E-mail: feruza.al@mail.ru
THE EFFECT OF ELEVATED TEMPERATURES ON THE CHLOROPHYLL CONTENT (A) IN THE LEAVES OF SOME MEDIUM AND FINE FIBER VARIETIES OF COTTON
Abstract. This article presents the results of studies on the effect of medium and high temperatures on the content of chlorophyll "a" in leaves of various varieties and cotton lines and on a comparative study of them with control variants. It was revealed that the high (hot) air temperature on the content of chlorophyll "a" in the leaves of the varieties Surkhan-14 (G.barbadense L.), Istiklol-14 (G.hirsutum L.) and the cotton line L-02, obtained on the basis of a hybrid G.hirsutum L. x G.sturtianum Müll. did not act significantly.
Keywords: chlorophyll a, medium and high temperature, deviation from control, homogenization, spectrophotometer, air humidity, pigment concentration.
1. Introduction
It is known that for the development of cotton the main environmental factors are their geographical origin, air temperature, light exposure, water regime and mineral nutrition. Among them, the air temperature plays an especially important role on the growth and development of plants and the biochemical and physiological processes occurring in them.
According to the World Meteorological Organization, last year there was an increase in the average temperature on the surface of the earth by + 1.1 °C, also 2015, 2016 and 2017 were recognized as the hottest, and the twentieth century - the hottest period in a millennium. Especially in the last decade of the twentieth century, there was a significant increase in the average temperature on earth (by 0.3-0.6 °C) [1].
Such climatic changes in recent years have caused tremendous damage to crops, in particular cotton. Thus, an in-
crease in the temperature of air and soil, as well as a decrease in relative humidity, depending on the biological, morpho-physiological characteristics of species, varieties and cotton lines, have a negative effect on their qualitative and quantitative characteristics. In scientific studies on the resistance of plants to unfavorable environmental factors, much attention is paid to the determination of chlorophyll a content, since The overall productivity of plants depends on the content of chlorophyll and its related forms.
It has been established that the content of chlorophyll "a" in cotton leaves varies depending on the characteristics of the species and varieties, as well as the environmental conditions. Cotton plant belongs to plants with a high content of chlorophyll in the leaves. Thus, in the varieties of cotton cultivated under conditions of high agrotechnics, the content of chlorophyll in the leaves is 300-400 mg per 100 g of weight [2].
THE EFFECT OF ELEVATED TEMPERATURES ON THE CHLOROPHYLL CONTENT (A) IN THE LEAVES OF SOME MEDIUM AND FINE FIBER VARIETIES OF COTTON
According to A. K. Tewari and B. C. Tripathy [3], the content of chlorophyll in cotton leaves depends on the characteristics of the variety and its physiological state. Under the action of elevated temperature, a change in the content of chlorophyll is observed.
In some plants, under conditions of elevated temperature, there is a shortage of moisture, as a result of which the diffusion of CO2 is somewhat activated. A prolonged lack of moisture in the next stages of development leads to a decrease in photosynthetic activity [4].
Slowing down the process of photosynthesis, most often, is associated with the closure of the stomata of leaves. In addition, it is advisable to study the effect of temperature on photosynthesis activity [5].
MD Kushnirenko believes that changes in temperature affect differently the activity of photosynthesis [6]. For example, low and short-term temperatures can partially activate this process. Under the action of elevated and prolonged temperatures, a sharp slowdown in photosynthesis was noted.
In the studies of A. Ergashov [7] on the effect of various high temperatures (+30, 40, 50, 60, 65 °C) on the cotton variety 108-F, a decrease in the chlorophyll content was observed as the air temperature increased. During the development of cotton plants, the highest content of chlorophyll in the leaves is noted in the budding phase. This indicates that an active assimilation process occurs in young plants. With the further development of cotton plants, the chlorophyll content gradually decreases. As is known, the ratio of chlorophyll to carotinoid in cotton does not exceed 3: 1. Cotton with a high content of chlorophyll yields a high yield [8].
As a response to the lack of water, wheat plants increase the content of strongly bound chlorophyll. In seedlings hardened to elevated temperatures, the content of chlorophyll "a", "b" and carotinoids is much higher than that of unhardened ones. In many wheat varieties, an increase in temperature is the cause of a decrease in the chlorophyll content [8].
From the above literature data it can be seen that, mainly, studies were carried out on old cotton varieties, and conclusions on their resistance to elevated temperatures were made on the content of total and bound chlorophyll. In our studies, cotton lines were used, obtained with the participation of some wild species, and varieties currently cultivated on large areas, the study of their resistance to elevated temperatures, based on the change in chlorophyll a content.
2. Materials and methods. The obj ects of research were the varieties of medium-fiber cotton G. hirsutum L. Sultan, Istiklol-14, Bukhara-102, fine-fiber cotton G. barbadense L. Surkhan-14, as well as lines L-01 and L-02 obtained using wild species G.klotzschianum Anderss., G.sturtianum Müll. respectively.
The experiments were carried out in the greenhouse complex Phytotron and at the vegetation site in an open area of the Research Institute of Breeding, Seed Production and Agricultural Technology of Cotton Cultivation, in Wagner's vessels in three versions: at the vegetation site at air temperature + 25-30 °C (I variant - control), in special boxes at a temperature of + 40-45 °C (II variant), and ultrahigh temperatures + 45-52 °C (III variant). In these boxes, the necessary conditions (elevated temperatures) were created in the flowering phase and the collection of fruit elements of the material under study.
To determine the content of chlorophyll "a" from 70-day plants (mass flowering phase), at the same time, from each variety and line, samples from 3-4 leaves from the growing point down were taken from all the experimental variants. Each sheet was thoroughly washed with running water, crushed, and 50 ml were placed in test tubes with 80% acetone solution (5 ml). These samples were homogenized for 10 minutes. in a centrifuge at 5000 rpm. The content of chlorophyll "a" in the resulting extract was determined on an Agilent Cary 60 UV-Vis spectrophotometer at a wavelength of 663.2.
Chlorophyll was determined by the formula (Lichtenthaler, Sumanta, 2014):
Chl "a" [mg/l] = 12.25*A663,2 - 2.79*A646,8
Chl "b" [mg/l] = 21.5*A646,8 - 5.1*A663,2 The stability index of chlorophyll was determined by the formula R. K. Sairam (1997):
Car [mg/l] = ((1000*A470) - (1.82*Chl a) --(85.02*Chl b))/198 The primary analysis of the obtained results was carried out using the Olingan EXCEL2010 program, dispersion analysis - (ANOVA, Fisher PLCD, alfa - 0.05) Stat View on a Pentium-4 computer.
3. Research results. In all studied varieties and cotton lines in different (3-variant) conditions of temperature and air, different content of chlorophyll "a" was noted. With an increase in temperature, all the studied varieties with minor deviations showed a decrease in the content of chlorophyll "a". Indicators of chlorophyll "a" in the leaves of the studied varieties and cotton lines in the first (control) variant at a temperature of + 30.9 °C and humidity 62.8% were located within 1.66 + 0.1-2.01 + 0.02 mg/l. At the same time, the highest content of chlorophyll "a" among the varieties was observed in Surkhan-14 (1.92 + 0.06 mg/l), among the lines - in L-02 with the participation of G.hirsutum L. x G.sturtianum Müll. (2.01 + 0.02 mg/l) (Table 1).
In the second experimental variant (at a temperature of 42.9 °C and humidity of 46.5%) the content of chlorophyll "a" was from 1.42 + 0.007 to 1.87 + 00.4 mg/l, the deviation from the control was downwards - 0.01; -0.02 mg/l, respectively. At the same time, positive indicators were observed in the Sur-
khan-14, Istiklol-14 and Sultan varieties, the difference with the control variants in which was -0.05,-0.01 and -0.03 mg/l, respectively (Table 1).
When determining the content of chlorophyll "a" in the third variant (temperature + 48.2o C, humidity 41.2%), it de-
Table 1.- Chlor
creased to 1.00 + 0.05-1.84 + 0.11 mg/l and the difference with the control amounted to -0.02 and 0.66. Here the highest content of chlorophyll "a" is observed in the line L-02. As can be seen from table 1, it is equal to 1.84+ 0.11 mg/l and exhibits a slight (-0.02 mg/l) deviation from the control.
hyll content "a"
Varieties and lines Contents chlorophyll "a" in the flowering phase, mg/g
x ± Sx limit V% difference
I Option-experience on the growing area (air temperature and humidity + 30.0 °C. 62.8%)
Surkhan-14 1.92 ± 0.06 1.84-2.0 0.11 -
Istiklol-14 1.75 ± 0.11 1.65-1.86 0.14 -
Sultan 1.70 ± 0.09 1.69-1.71 0.01 -
Bukhara-102 1.73 ± 0.03 1.69-1.76 0.05 -
L-01 (G.hirsutum L. x G.klotzshianum Änderss) 1.66 ± 0.10 1.55-1.76 0.14 -
L-02 (G.hirsutum L. x G. Stursianum Muii) 2.01 ± 0.02 1.97-2.04 0.03 -
II Option - in conditions of elevated temperatures (air temperature and humidity + 42.9 °C. 46.5%)
Surkhan-14 1.87 ± 0.04 1.78-1.94 0.084 -0.05
Istiklol-14 1.74 ± 0.06 1.61-1.81 0.11 -0.01
Sultan 1.67 ± 0.02 1.65-1.69 0.02 -0.03
Bukhara-102 1.61 ± 0.08 1.51-1.78 0.14 -0.12
L-01 (G.hirsutum L. x G.klotzshianum Änderss) 1.42 ± 0.007 1.41-1.44 0.01 -0.24
L-02(G.hirsutum L. x G. Stursianum Muii) 1.86 ± 0.01 1.85-1.87 0.018 -0.15
III Option - in conditions of high temperatures (air temperature and humidity + 48.2 °C. 41.2%)
Surkhan-14 1.73 ± 0.03 1.69-1.77 0.056 -0.19
Istiklol-14 1.49 ± 0.01 1.47-1.50 0.22 -0.26
Sultan 1.59 ± 0.08 1.50-1.68 0.12 -0.11
Bukhara-102 1.45 ± 0.07 1.37-1.52 0.10 -0.28
L-01 (G.hirsutum L. x G.klotzshianum Änderss) 1.00 ± 0.05 0.96-1.07 0.07 -0.66
L-02 (G.hirsutum L. x G. Stursianum Muii) 1.84 ± 0.11 1.73-1.96 0.16 -0.02
4. Conclusion. From the obtained results it follows that this regard, these varieties can be recommended as a starting
the content of chlorophyll "a" in the cotton varieties of Sur- material for genetic selection studies on resistance to elevated
khan-14, Istiklol-14 and the line L-02 (obtained on the basis temperatures (heat resistance) and to create varieties with
of G. hirsutum L. x G.sturtianum Müll.) Was insignificant. In high photosynthetic activity.
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