Effect of kinetin concentration and methods of application
on seed germination, yield components, yield and fiber
properties of the Egyptian cotton (
Gossypium barbadense
)
Z.M. Sawan
a,*, A.A. Mohamed
b, R.A. Sakr
b, A.M. Tarrad
caCotton Research Institute,Agricultural Research Center,Ministry of Agriculture & Land Reclamation,9 Gamaa Street,12619,
Giza, Egypt
bDepartment of Agricultural Botany,Faculty of Agriculture,Cairo Uni
6ersity,Giza, Egypt
cField Crops Research Institute,Agricultural Research Center,Ministry of Agriculture & Land Reclamation,9Gamaa Street, 12619,Giza, Egypt
Received 28 January 2000; received in revised form 3 April 2000; accepted 4 April 2000
Abstract
Two field experiments in 1993 and 1994 as well as a laboratory germination experiment were conducted on the Egyptian cotton cultivar Giza 75 (Gossypium barbadense) to determine the effect of six concentrations of kinetin (6-furfurylaminopurine) ranging from 0 to 10.0 mg l−1 and three different methods of application: (A) seeds were
soaked for 24 h before germination (laboratory experiment) or sowing (field experiment) in solutions of different kinetin concentration, (B) cotton plants were sprayed twice with different kinetin concentrations at 60 and 75 days after sowing (DAS) during the square initiation and the beginning of bolling stages, at volume solution of 480 l ha−1.
(C) Seeds were soaked in kinetin solutions before sowing as method A. In addition cotton plants were sprayed twice as method B with the same kinetin concentrations. Kinetin application improved seed viability and seedling vigour as shown by lengths of the hypocotyl, radicle and the entire seedling, as well as seedling fresh weight. Moreover, significant increases were recorded in the number of open bolls/plant, boll weight, lint and seed indices, seed cotton yield/plant, and seed cotton and lint yields/plot. The highest means were obtained at 5 mg kinetin l−1concentration
and under method C of application. Treatments generally, had no significant effects on lint percentage, yield earliness and fiber properties. These results show that, the use of kinetin at 5 mg l−1for pre-soaking seeds before planting and
spraying cotton plants at 60 and 75 DAS with the same concentration could improve cotton germination, seed cotton and lint yields. © 2000 Elsevier Science B.V. All rights reserved.
Keywords:Cotton; Fiber properties; Germination; Kinetin; Lint; Yield
www.elsevier.com/locate/envexpbot
* Corresponding author..
E-mail address:abeer.gomaa@ncr.com.eg (Z.M. Sawan).
Z.M.Sawan et al./En6ironmental and Experimental Botany 44 (2000) 59 – 68
60
1. Introduction
Cotton is the most important fiber crop in the world as well as in Egypt. Increasing cotton production and quality is an urgent national goal to meet the consistent demand for this crop. Plant development is influenced by various endogenous and exogenous factors. The result-ing physiological processes regulate the rhythm of growth and development. A group of sub-stances that is of particular interest in this re-spect are the bioregulators.
Plant growth regulators (PGRs) usually are defined as organic compounds, other than nutri-ents, that at low concentrations, affect the phys-iological processes of plants (Glemas, 1982). For practical purposes, PGRs can be defined as ei-ther natural or synthetic compounds that are applied directly to a plant to alter its growth processes or structure in some beneficial way (Luib and Schott, 1990).
Growth and development processes in plants are coordinated by phytohormones (Bruinsma, 1980). They can also be influenced, however, by the exogenous application of specific bioregula-tors. The specific effect of a bioregulator de-pends on the application rate, time of treatment, and the developmental stage of the plant at the time of application (Do¨rffling, 1982).
The cytokinins (CK) play an important role in all phases of plant development, from cell division, and cell enlargement up to the tion of flowers, fruit set and dry matter forma-tion in plants (Mayeux, 1985; Cothren, 1994). The basis for foliar application of cytokinins to
field plants is inferred from the improved
growth of plants in cytokinin-containing solu-tions (Hedin and McCarty, 1994b). Cytokinins may not always be active unless other hormones are present (Hedin and McCarty, 1994b). How-ever, cytokinins alone can often evoke a variety of physiological, metabolic, biochemical, and de-velopmental processes when applied to plants (Elliott, 1982; Taiz and Zeiger, 1991).
Cytokinins are synthesized in root tips and are active in the maintenance of ongoing pro-cesses and nutrient mobilization in the shoot (Hearn and Constable, 1984). Thus they inhibit
shedding by stimulating auxin production. Peak CK activity in bolls is at 4 – 9 days after flower-ing, declining to little or none at 18 days (Sand-stedt, 1971). It is hoped that if the endogenous concentration of cytokinin can be increased by exogenous application, it may reduce the unde-sirable shedding of squares and bolls which may lead to an increase in seed cotton yield.
The use of PGRs on cotton has been investi-gated by many workers including McCarty et al. (1987), Hedin and McCarty (1991, 1994b). Fo-liar spraying revealed that the synthetic cy-tokinin, kinetin (6-furfurylaminopurin), tended to increase yield of cotton. Hedin and McCarty (1991, 1994b) found that kinetin applied in the field increased cotton yield by 26%. Deng Ji-anXiu (1996) spraying cotton plants with a mix-ture of 4 PU-30 (synthetic cytokinin) and DPC (mepiquate chloride) increased lint yield by mainly 17% compared with water only, and by mainly 7% compared with spraying DPC only. Foliar application of this cytokinin products was reported to promote bud initiation and develop-ment that caused an increase in plant fruitful-ness and increased efficiency of the plant to develop and fill that fruit (Mayeux, 1985). Oost-erhuis et al. (1997) found that Maxon (cy-tokinin) application produced a significantly greater number of open bolls 7 weeks after first flower. El-Aggory et al. (1982) reported that kinetin significantly increased seed cotton yield and number of mature bolls. Lint strength or fineness did not change with any of the kinetin treatments.
2. Materials and methods
2.1. I. Germination experiment
Germination was evaluated using the Interna-tional Rules for Seed Testing (ISTA, 1976). Cot-ton seeds (Gossypium barbadense L. cv. Giza 75) were soaked for 24 h in six concentrations of kinetin (6-furfurylaminopurine) (0, 0.25, 0.5, 1.0, 5.0 and 10.0 mg l−1) before germination.
Alu-minium dishes (17 cm in diameter and 3 cm deep) were used. Sand was used as substrate with pH values within the range 6.0 – 7.5, which must be free from foreign seeds and sterilized at 250°C for 4 h to avoid infestation by fungi, bacteria or toxic substances. It was sieved to receive reasonably uniform sand particles (\0.05 – 0.8 mm diame-ter), washed, sterilized and kept moistened. Fifty pre-soaked seeds were placed in each dish in a 2-cm deep sand depression made with a standard puncher. Each concentration included four repli-cates of two dishes (100 seeds per replicate). Dishes were then incubated in a darkened germi-nator at 3091°C for 96 h, after which the per-centage of seeds which germinated was recorded for seed viability. Seedling vigour was recorded from 10 seedlings which were randomly selected from each dish; lengths of hypocotyl, radicle and entire seedling were measured. The 10 seedlings were weighed immediately to record fresh weight.
2.2. II. Field experiment
Two field experiments were performed during the 1993 and 1994 seasons at the Agricultural Research Center Experimental Station, Giza, Egypt, with the cultivar Giza 75. The soil type in both seasons was a clay loam with alluvial sub-stratum (pH: 8.10); 44.1% clay; 27.8% silt; 18.9% fine sand; 4.22% coarse sand; 2.98% calcium car-bonate and 1.82% organic matter. The field ca-pacity (0 – 60 cm) was 35%. Total water supply during the growing season was about 6000 m3per
hectare.
Each experiment consisted of 18 treatments of the following combinations: six different concen-trations of kinetin (0, 0.25, 0.5, 1.0, 5.0 and 10.0 mg l−1) and three different methods of
applica-tion: (A) seeds were soaked for 24 h in different kinetin solutions before sowing; (B) cotton plants were sprayed with 480 l ha−1 (uniform coverage
of leaves) at 60 and 75 DAS (square initiation and the beginning of boll filling) with different kinetin solutions; and (C) methods A+B.
The experimental design was a randomized complete block with four replications. Seeds were sown on March 24 and April 8 in 1993 and 1994, respectively, in plots consisting of 5 rows 3 m wide×4 m long. Hills were spaced 20 cm apart in rows. Plants were thinned to two plants per hill after 6 weeks to attain plant density of 16.6 m2
. The first irrigation was given 3 weeks after sow-ing, and the second 3 weeks later, thereafter the plots were irrigated every 2 weeks until the end of the season for a total of nine irrigations. Phospho-rus was applied before sowing at a rate of 24 kg P ha−1 as calcium superphosphate (6.5% P).
Potas-sium was applied before the first irrigation at a rate of 47 kg K ha−1 as potassium sulfate (40%
K) (3 weeks after sowing). Nitrogen was applied
at the rate of 144 kg N ha−1 as ammonium
nitrate with lime (33.5% N) in two equal amounts, 6 and 8 weeks after sowing; each application was followed immediately by irrigation.
Z.M.Sawan et al./En6ironmental and Experimental Botany 44 (2000) 59 – 68
62
fiber maturity) measured by a Micronaire instru-ment, and (iii) flat bundle strength (expressed in terms of strength weight ratio ‘s.w.r.’) measured by the Pressley index (according to Annual Book of ASTM Standards, D 1447-77, D 1448-79, and D 1445-75, respectively, 1979). Results were ana-lyzed as a factorial experiment (Snedecor and Cochran, 1980).
3. Results
3.1. Seed6iability and seedling 6igour
Seed viability (germination percentage) and seedling vigour (lengths of hypocotyl, radical and entire seedling; as well as seedling fresh weight) significantly exceeded the seedling of the control (24 h in water only) when the seeds were soaked for 24 h in kinetin solution at concentrations varying between 0.5 and 10.0 mg l−1 (Table 1).
Soaking seeds in kinetin solution of 0.25 mg l−1
or more had a significant effect on radicle and seedling lengths compared to the untreated con-trol; generally, 10 mg l−1
induced great significant increments than 0.25 mg l−1
.
3.2. Yield components
3.2.1. Number of opened bolls per plant
Kinetin at concentrations over 0.25 mg l−1
increased the number of opened bolls per plant in both seasons, as compared with the control (Table 2). The 5 mg l−1 treatment produced the highest
number of opened bolls/plant. The kinetin appli-cation methods, i.e. foliar appliappli-cation (B) and a combination of soaking and foliar applications (C) increased the number of opened bolls per plant over seed soaking in both seasons. This increase was significant for application methods B and C in 1993 and for application method C in 1994. The number of opened bolls per plant was numerically the greatest from the application method C.
3.2.2. Boll weight
Boll weight was increased by the different con-centration treatments of kinetin over the
un-treated control in the two seasons (Table 2). The increases were significant for the kinetin concen-trations ranging from 0.5 to 10.0 mg l−1 in 1993
and from 1.0 to 10.0 mg l−1in 1994. The 5.0 mg
l−1 concentration produced the largest boll
weight. Kinetin application methods B or C in-creased the boll weight as compared with method A in both seasons. This increase was significant with method C in 1993, and methods B and C in 1994, with no statistically significant differences between them. Method C produced the highest boll weight.
3.2.3. Lint percentage
Kinetin did not cause any significant changes in lint percentage in either season despite a slight numerical trend for an increase in lint percentage compared with the untreated control. Application method B slightly increase lint percentage over methods A and C in 1994.
3.2.4. Seed index
Kinetin applications increased seed index in both seasons, as compared with the control (Table 2). The increase was significant for all concentra-tions in 1993, and for 0.50 – 10.0 mg l−1
in 1994. The largest increase in the seed index was found in the case of 5.0 mg l−1concentration, followed
by 10.0 mg l−1. Method C was superior to
method A in both seasons, while method B was better only in 1994.
3.2.5. Lint index
Lint index significantly increased with all kinetin concentrations in both seasons (Table 2); the differences among rates were not significant. The methods B and C proved superior to method A in both seasons.
It is worthy to mention that the effects of the interaction between kinetin concentrations and application method on all yield component char-acters were statistically insignificant.
3.3. Yield
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Table 1
Effect of soaking cottonseeds in solutions of different kinetin concentrations for 24 h before planting on seed viability and seedling vigour
Kinetin concentration Germination percentage (%) Hypocotyl length Radical length Seedling length Seedling fresh weight (g/10 seedlings) (cm)
(cm) (cm)
(mg l−1)
Actual Arc sinea
13.090.28 6.4390.237 8.2690.160
4.7490.133 0.00 (Control) 77.091.29b 61.490.88
8.9590.115 13.990.17 6.5690.092 78.591.70 62.491.18
0.25 4.9490.668
5.1290.098 9.1090.092 14.290.18 6.8190.072 82.590.95
0.50 65.390.71
14.690.38 6.7990.049 9.1990.258
85.590.95 67.790.79 5.4090.124 1.00
9.1590.188 14.790.31 7.0790.050 86.091.82 68.291.51 5.5490.131
5.00
5.4190.119 9.0890.163 14.590.27 7.2190.173 10.00 87.091.29 68.991.10
0.159 0.239 0.39 0.166 1.98
SEc 1.53
0.83 0.355 0.510
0.340 4.22 3.28
LSDd
aArc sine=Angles corresponding to percentage. b9Standard error of the respective averages.
cSE=Standard error for the differences among averages.
Z.M.Sawan et al./En6ironmental and Experimental Botany 44 (2000) 59 – 68
64
Table 2
Effect of kinetin concentration and methods of application on yield components of cottona
Kinetin application method Kinetin concentration (mg l−1)
C Average A B
B C Average
A
1994 1993
Number of opened bolls/plant
0.00 (control) 12.8 12.9 12.9 12.8 13.2 13.2 13.2 13.2
13.4
0.25 12.9 13.0 13.1 13.4 13.4 13.7 13.5
13.8 13.4 13.6 13.9
13.4 14.2
0.50 13.0 13.9
13.5
13.0 13.9 13.4 13.5 14.0 14.5 14.0
1.00
14.1 13.6 13.8 14.2
5.00 13.2 13.5 14.7 14.2
13.8 13.6 13.6 14.3
13.8 14.5
13.2 14.2
10.00
13.4
13.0 13.6 13.5 13.8 14.1
Average
SE kinetin concentration 0.22 0.27
0.19 0.16
SE application method
SE for interaction 0.39 0.46
Boll weight(g)
2.26
2.28 2.27 2.27 2.24 2.24 2.25 2.24
0.00 (control)
2.36 2.33 2.25 2.32
0.25 2.31 2.32 2.30 2.29
2.40 2.36 2.24 2.35
2.35 2.36
2.33 2.32
0.50
2.38
2.33 2.41 2.37 2.25 2.35 2.43 2.34
1.00
2.42 2.39 2.31 2.36 2.51 2.39
5.00 2.33 2.42
2.43 2.39 2.26 2.33
2.39 2.44
10.00 2.34 2.36
2.38 2.26
Average 2.32 2.35 2.33 2.38
0.046 SE kinetin concentration 0.032
0.033 0.023
SE application method
SE for interaction 0.056 0.080
Lint percentage(%)
34.0 34.0 33.3
0.00 (control) 34.1 34.0 33.7 33.5 33.5
0.25 34.0 34.1 34.2 34.1 33.4 33.9 33.5 33.6
0.50 34.2 34.6 34.3 34.4 33.3 33.7 33.5 33.5
34.2 34.3 33.3 33.9
34.7 33.4
1.00 34.1 33.5
34.7
34.2 34.2 34.4 33.4 33.7 33.5 33.6
5.00
34.2 34.3 33.5 33.8 33.6 33.6
10.00 34.2 34.3
34.2 33.4 33.8 33.5
34.4 SE for interaction 0.40
Seed index(g)
1.00 10.0 10.1 10.0 10.0
10.2 10.2 9.9 10.0
Average 10.0 10.1 10.2 9.9 10.0 10.0
0.06 SE kinetin concentration 0.07
0.04 0.05
SE application method
SE for interaction 0.13 0.11
Lint index(g)
5.13 5.11 5.10 5.11 4.90 5.00 4.94 4.95
0.00 (control)
5.16 5.24 5.27 5.22 4.92 5.12 5.03 5.02
0.25
5.32 5.29 4.91 5.09
5.36 5.05
0.50 5.21 5.02
5.31 5.30 4.93 5.12 5.04 5.03
1.00 5.20 5.38
5.33 5.31 4.98 5.11
5.39 5.10
5.00 5.21 5.06
5.30
5.23 5.32 5.28 4.99 5.12 5.09 5.07
10.00
5.27 4.94
Average 5.19 5.30 5.09 5.04
0.035
Table 3
Effect of kinetin concentration and methods of application on cotton yielda
Kinetin application method Kinetin concentration (mg l−1)
A B C Average A B C Average
1993 1994
Seed cotton yield(g/plant)
29.1 29.2
0.00 (control) 29.1 29.2 29.6 29.7 29.7 29.7
30.2 30.6
0.25 29.9 30.6 30.2 31.0 31.4 30.9
31.6 33.1 31.6 30.5
30.2 32.5
0.50 33.4 32.1
32.1 33.4 31.9
1.00 30.3 30.4 32.8 35.1 32.8
32.7 34.1 32.5 31.8
30.9 33.6
5.00 36.7 34.0
30.8
10.00 32.9 33.6 32.5 30.8 33.9 35.4 33.4
Average 30.2 31.4 32.5 30.5 32.2 33.6
0.53 0.67
SE kinetin concentration
0.47
SE application method 0.38
SE for interaction 1.16 0.93
Seed cotton yield(kg/plot)
3.30 3.30 3.30
0.00 (control) 3.29 3.38 3.38 3.39 3.38
3.42 3.60 3.47
0.25 3.38 3.44 3.55 3.58 3.52
3.51 3.68 3.52 3.47
3.36 3.71
0.50 3.79 3.66
3.43
1.00 3.63 3.77 3.61 3.47 3.74 3.99 3.73
3.76 3.88 3.73 3.62
3.55 3.82
5.00 4.18 3.87
3.50
10.00 3.74 3.86 3.70 3.51 3.86 4.02 3.80
Average 3.42 3.56 3.68 3.48 3.68 3.83
0.063 0.081
SE kinetin concentration
0.057
SE application method 0.044
SE for interaction 0.141 0.109
Lint yield(kg/plot)
1.12 1.12 1.12
0.00 (control) 1.12 1.13 1.14 1.14 1.13
1.17 1.23 1.18
0.25 1.15 1.15 1.20 1.20 1.18
1.21 1.26 1.21 1.16
1.15 1.25
0.50 1.27 1.23
1.00 1.17 1.26 1.29 1.24 1.16 1.27 1.34 1.25
1.30 1.33 1.28 1.21
1.21 1.29
5.00 1.40 1.30
1.29 1.32 1.27 1.17 1.31 1.35
10.00 1.20 1.28
1.23 1.26 1.16 1.24 1.28
1.17 Average
0.023 0.027
SE kinetin concentration
SE application method 0.019 0.016
0.040 0.047
SE for interaction
aSE=Standard error.
10.0 mg l−1
in both seasons (Table 3). The highest increase in cotton yield was achieved at 5.0 mg l−1
, followed by 10.0 mg l−1
. These two kinetin concentrations significantly increased the seed cotton yield per plant and per plot compared with the 0.25 mg l−1 in both years, and, along
with the 1.0 mg l−1treatment also produced more
lint yield per plot than 0.25 mg l−1. Application
method B or C significantly increased the cotton yield, as compared with method A in both
sea-sons, without any significant differences between method B or C. The highest numerical increase was obtained from method C.
3.4. Yield earliness
con-Z.M.Sawan et al./En6ironmental and Experimental Botany 44 (2000) 59 – 68
66
centrations ranging from 0.25 to 5.0 mg l−1 and
application methods A and C resulted in a slight numerical reduction in yield earliness.
3.5. Fiber properties
Kinetin application did not significantly affect fiber length parameters (2.5 and 12.5% span lengths and uniformity ratio), micronaire reading or flat bundle strength in either season, with only one exception, where micronaire reading increased compared with the untreated control in 1994. This increase in micronaire reading was significant when applying concentrations of kinetin ranging from 0.5 to 10.0 mg l−1. The mean values of these characters
tended to slightly increase by applying kinetin at different concentrations when compared with the control. The kinetin application methods did not affect fiber properties in either season, with two exceptions where fiber 12.5% span length and flat bundle strength increased when applying method B as compared with method A. Fiber 2.5 and 12.5% span lengths, micronaire reading and flat bundle strength tended to increased slightly by using application method B, followed by application method C, compared with application method A, while length uniformity ratio did not follow a definite trend.
3.6. Interactions
Interactions were noted between kinetin concen-trations and kinetin application methods regarding their effects on seed cotton yield per plant and seed cotton and lint yields per plot in 1994 (Table 3), but not on other measured characters. Favourable effects for 5.0 mg l−1 kinetin concentrations on
seed cotton yield per plant and seed cotton and lint yield per plot, were more obvious when kinetin application method C was used.
4. Discussion
4.1. Seed6iability and seedling 6igour
The stimulatory effect of kinetin application on seed viability and seedling vigour could be
at-tributed to its favourable effects on synthesis of RNA, proteins, and enzymes, causing a general metabolic advancing or priming to occur (Moore, 1989). Actually, cytokinins might be rapidly incor-porated into micromolecules such as RNA. On the basis of their findings, it could be stated that cytokinins promote RNA and protein synthesis and that exogenous cytokinins often have highly localized effects when applied to whole plants and plant organs (Moore, 1989). The stimulative effect of kinetin on germination and seedling vigour observed in the present study agrees with the findings of Bozcuk (1990) and Kabar (1990) with cotton and Singh and Amritphale (1993) with soybean.
4.2. Yield components
Rodgers (1981) made a comparative analysis of retained and naturally abscising cotton fruits and found that abscission was negatively correlated with the concentration of cytokinins. Therefore, foliar applications of this chemical to cotton plants should reduce flower bud and young boll shed and promote fruit growth. Mayeux (1985) showed that Burst (a commercial cytokinin product) applied at early bloom or applied at mid bloom significantly increased the boll set and fruiting of cotton plants. Similar findings were obtained by Oosterhuis et al. (1997). The positive response of boll weight to kinetin application might be explained by the physiological, metabolic, and biochemical effects of kinetin. In this respect Gadallah (1995) found that application of kinetin (at 10, 50 or 100 mg kinetin l−1) to castor bean (Ricinus communis) plants
(Mayeux, 1985) which would enhance their growth leading to initiation and development of greater number of fibers per seed (Skoog and Armstrong, 1970).
4.3. Yield
These results may be attributed to the promot-ing effect of this substance on numerous physio-logical processes, leading to an improvement in all yield components. Guinn and Brummett (1993) stated that cytokinins have been reported to increase stomatal aperature and stimulate photosynthesis. Bauer and Cothren (1986) indi-cated that an increase in photosynthesis greatly increased flowering, boll retention, and yield. Parker and Salk (1990) and Hedin and McCarty (1994a) reported that kinetin increased seed cot-ton yield. Namken (1984) also found that cy-tokinin applications increased lint cotton, while Dhopte and Lall (1987) found that a foliar spray of 10 mg l−1 kinetin at the flowering stage,
in-creased dry matter production, dein-creased boll shedding and increased seed cotton yield.
4.4. Yield earliness
Namken (1984) found that there were no sig-nificant differences in earliness due to cytokinin treatments.
4.5. Fiber properties
Namken (1984) found that there were no sig-nificant differences in fiber properties (mi-cronaire, length, uniformity, and strength) due to cytokinin treatments. Abdel-Al et al. (1989) found that application of cytokinin had no sig-nificant effect on micronaire reading and flat bundle strength. Hofmann and Else (1989) found that kinetin had no significant effect on fiber quality.
5. Conclusions
The results of the present study indicated that kinetin treatments increased cotton yield. The
obtained data indicated that the use of kinetin at a 5 mg l−1 rate as a pre-soaking treatment
be-fore planting and spraying plants at 60 and 75 DAS with the same concentration might be a useful practice for commercial production of cot-ton. As such effects have been seen, the impor-tant question is whether they can be translated successfully to farmer’s fields. This increase should be economically evaluated under different environmental conditions and with different cot-ton cultivars. In comparison with the ordinary cultural practices adopted by Egyptian cotton producers, it is quite apparent that application of such growth regulator could bring about bet-ter cotton productivity and betbet-ter fiber quality. Thus, PGR chemicals could become a useful tool in the cotton producers reserve to ensure efficient production. However, it seems that fur-ther research work should be conducted to provide further information which would cover other aspects related to physiological mecha-nisms affecting cotton productivity.
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