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Comparison of Bt and non-Bt cotton cultivars for earliness indicators
335
COMPARISON OF BT AND NON-BT COTTON (GOSSYPIUM
HIRSUTUM L.) CULTIVARS FOR EARLINESS INDICATORS AT
DIFFERENT SOWING DATES AND NITROGEN LEVELS
M. Sarwar, M. Farrukh Saleem, M. Ashfaq Wahid*, Amir Shakeel**
and M. Faisal Bilal*
ABSTRACT
Bt and non-Bt cotton (Gossypium hirsutum L.) cultivars were compared for
different earliness indicators in the Department of Agronomy, University of
Agriculture, Faisalabad, Pakistan during the year 2010. In this study two cotton
cultivars MNH-786 (non-Bt) and IR-1524 (Bt), three nitrogen levels (115, 145 and
175 kg/ha) and two sowing dates (mid March and mid May) were included.
Layout system was RCBD with split split plot arrangement in a plot measuring
6.0 x 4.5 m. Nitrogen levels and sowing dates showed significant effect on
earliness related parameters. Nitrogen level of 115 kg per hectare showed more
earliness index (59.2) than 145 kg (51.1) and 175 kg N (48.5). Nitrogen level of
115 kg also took less number of days for floral bud initiation (30.5), flowering
(50.1), first boll splition (93.1) and also less number of days to node above
white flower (95.9). With regards to sowing date, May sowing produced more
earliness index (57.5) and less number of days for floral bud initiation (30.5),
flowering (49.6), first boll splition (91.1) and less number of days to node above
white flower (99.4) than mid March sowing. Both cultivars showed nonsignificant
differences in earliness related parameters with relatively more
earliness in non-Bt cultivar than Bt cultivar. The study concludes that 115 kg N
per hectare and mid May sowing produced early maturity in cotton.
KEYWORDS: Gossypium hirsutum; Bt varieties; sowing; timing; nitrogen
fertilizer; agronomic characters; Pakistan.
INTRODUCTION
After initiation of flowering in cotton (Gossypium hirsutum L.), vegetative
growth continues due to its indeterminate and perennial habit but cotton is
grown as an annual crop. Cotton plant has ability to overcome the fruit
abscission and fruit damaging due to its growth and fruit pattern without yield
reduction. However, it may increase the risk of insect attack and may also
*Department of Agronomy, **Department of Plant Breeding and Genetics, University of
Agriculture, Faisalabad, Pakistan.
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delay the crop harvest. It indicates that yield recovery is only possible when
the plant is young (23).
Cotton growth and maturity are altered by cultivars, seasonal management
and environmental conditions (11). Early maturity of cotton cultivars allows
timely removal from the field, helps the crop to fit in double cropping system
and can overcome the problem of water shortage (8, 24).
Nitrogen is the integral part of chlorophyll, protein, nucleic acids,
biomolecules, chromosomes and phytochromes (21, 22). Nutrients affect the
photosynthesis, leaf area of the crop (6) and supply of carbohydrates to sink
of the crop. To prevent the bolls and squares from abscission, nitrogen is
important controlling factor (6, 27). Khan (20) observed that a mineral nutrient
such as nitrogen is essential to attain higher yield of agricultural crops and
exploit the crop potential. Ahmad (1) reports that nitrogen is important
nutrient for cotton yield in irrigated areas. In some other studies (3, 33)
earliness reduced with increasing levels of nitrogen. High nitrogen availability
caused excessive vegetative growth thus delaying crop maturity and reducing
yield by shifting the balance between vegetative and reproductive growth
(14).
In early sown cotton, there is a serious reduction in yield because
reproductive stages of the crop come in hottest months of the year. Crop
sown in too early season has shown lower crop yield and lower crop stand,
while crop sown in too late season of year resulted in excessive vegetative
growth and reduction in yield. So for better crop management proper sowing
time is the key factor in any region (34). The primary factor affecting crop
development is temperature and initiation of first square and its development
was temperature and cultivar dependant (13). Plant development rate is
much increased at high temperature (15, 28, 29) shortening plant life period.
Cotton earliness, a quantitative trait, is mainly affected by environment and
crop genotype (18). Therefore, in any cropping system cultivar selection is
the key factor (25). Keeping in view the importance of earliness in cotton crop
response of cotton crop to nitrogenous fertilizers and sowing dates, the
present study was conducted to identify the cultivar that can fit well in our
cotton-wheat cropping system.
MATERIALS AND METHODS
This study was conducted in the Department of Agronomy, University of
Agriculture, Faisalabad, Pakistan during kharif 2010. The soil of experimental
site was sandy clay loam with alkaline pH (7.4), 0.65 percent organic matter,
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Comparison of Bt and non-Bt cotton cultivars for earliness indicators
337
0.039 percent N, 7.85 ppm available phosphorus and 220 ppm available
potassium. Layout-system was RCBD with split split arrangement replicated
thrice. Plot size was 6x 4.5 m. Experimental treatments comprised three
nitrogen levels viz. 115 kg (N 1 = recommended for non-Bt), 145 kg (N 2 =
medium dose) and 175 kg per hectare (N 3 = recommended for Bt cotton),
two sowing dates viz. mid March (S 1 = recommended for Bt) and mid May (S 2
= recommended for non-Bt) and two cotton cultivars viz. MNH-786 (V 1 = non-
Bt) and IR-1524 (V 2 = Bt).
Each plot contained six rows of cotton crop. Seedbed was prepared by
cultivating the field one time with rotavator and two times with tractormounted
cultivator each followed by planking. The crop was sown on March
14 and May 15, 2010 with help of dibbler by maintaining 0.75 m row to row
and 0.30 m plant to plant spacings. Full dose of phosphorus was applied at
sowing while nitrogen was applied in three equal splits viz. at sowing, 35 days
after sowing (squaring stage) and 65 days after sowing (flowering stage).
Crop was given nine irrigations throughout its growth period. Weeds were
controlled by two hoeings viz. 35 and 65 days after planting while insects
were controlled with insecticides. All other agronomic practices were kept
normal and uniform for all treatments. When seedlings were established, ten
true representative plants were selected randomly from each plot. These
plants were monitored and tagged to record the following data:
Days from planting to first floral bud initiation
Data on number of days from planting to first floral bud initiation [the days
when subtending leaf unfolded (7)] were recorded from ten selected plants of
each plot, when bud beam became visible with the naked eye having a pin
head size of about 3 mm.The data were recorded from the selected plants
when 50 percent selected plants showed squaring.
Days from planting to appearance of first flower
Number of days from planting to appearance of first flower were noted when
50 percent of selected plants showed flowering with creamy white or
yellowish colour of flower.
Days to node above white flower
Data on this trait were recorded from selected plants after one week of
flowering and continued till appearance of five nodes above white flowers.
Data were noted weekly in days and average of selected plants was
calculated.
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Days from planting to first boll splition
This parameter was noted when lint was seen within the boll with squares
around (cracked boll) and took average of selected plants.
Earliness index (%)
Earliness index (%) was calculated with following formula (35).
Earliness index (%) = Weight of seed cotton from first pick × 100
Total seed cotton weight from all picks
Growing degree days (DD 60°F)
Minimum or base temperature for cotton growth is 60°F. Daily heat units or
degree days (DD60s) as given in Table 1 were calculated as defined by
Bendnarz and Burmester (5).
Table 1.
DD60 °F =
Day time high °F + Night time low °F-60
2
Growing degree days (DD 60°F) during cotton growing period.
S. March April May June July August September October November
No.
1 6.25 10.5 13.75 19.25 21.75 17.0 15.75 13.25 7.5
2 6.5 11.5 18.25 21.5 24.25 16.0 16.25 13.5 8.5
3 6.0 9.75 17.5 19.0 15.0 16.0 17.0 13.75 5.75
4 1.75 12.5 19.75 17.5 18.0 15.75 16.75 13.5 5.75
5 2.5 12.0 20.75 16.5 17.5 16.75 14.25 13.25 6.5
6 4.0 11.25 11.25 15.25 15.5 16.0 15.5 13.25 5.75
7 0.5 19.25 12.5 15.75 16.0 14.0 16.25 13.0 5.75
8 2.5 22.75 13.5 14.25 17.75 15.5 15.25 13.0 5.0
9 4.0 23.0 14.5 15.0 19.5 14.5 13.25 12.5 5.5
10 5.25 23.0 16.0 15.0 20.75 16.0 12.75 12.5 4.5
11 5.5 24.25 16.5 17.0 21.5 17.0 14.0 11.75 4.0
12 6.0 24.25 15.5 18.25 15.0 13.5 14.0 12.0 4.0
13 6.0 24.0 17.5 19.25 11.5 14.75 12.5 11.5 4.5
14 7.25 23.5 15.0 19.25 14.25 16.25 13.0 11.5 3.5
15 8.5 25.75 18.5 14.25 16.25 15.75 8.5.0 12.5 2.75
16 8.75 17.75 18.5 15.5 19.0 14.0 12.25 13.0 2.25
17 9.25 17.25 19.0 16.75 19.75 13.75 13.5 12.5 2.0
18 9.5 18.5 17.5 18.0 18.5 16.25 10.0 11.75 2.5
Table 1 contd…..
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19 9.5 16.75 14.5 20.5 17.75 16.5 9.5 12.5 2.0
20 10.25 17.0 16.0 22.5 14.5 16.0 9.5 12.0 1.75
21 11.5 15.0 16.5 22.5 10.25 15.65 12.75 11.25 1.25
22 10.5 14.25 22.0 24.5 10.75 15.25 11.0 8.5 2.0
23 12.5 11.5 22.75 21.75 12.0 16.25 13.25 6.0 1.0
24 12.0 13.5 21.25 18.25 14.0 13.25 12.25 6.0 0.5
25 11.25 14.5 20.75 17.75 16.0 13.5 12.0 6.5 0.75
26 12.25 16.0 19.5 16.5 19.0 10.5 12.0 7.0 2.0
27 11.5 16.0 24.25 20.5 17.0 10.75 11.75 6.0 1.0
28 10.5 16.5 22.25 20.5 13.25 13.25 13.0 6.75 0.5
29 11.5 16.25 15.5 22.0 12.75 14.25 12.5 7.0 0.5
30 12.25 14.5 16.5 17.25 14.0 16.0 12.25 7.25 -0.25
31 11.0 16.75 16.25 15.5 0.5
Data collected on different parameters were analyzed statistically by using
MSTAT-C (4) for analysis of variance. Means were separated using Fisher's
protected least significant difference (LSD) test at 5 percent probability level
(36).
Days to first floral bud initiation
RESULTS AND DISCUSSION
The data (Table 2) indicated that this trait was significantly influenced by
sowing dates and nitrogen levels while cultivars and all first order and second
order interactions showed non-significant effects. Relatively less days to
squaring were noted in non-Bt cultivar MNH-786 (32.9) than Bt cultivar IR-
1524 (33.6) (Table 2). Mid March sowing took more days for floral bud
initiation (36.0) than mid May sowing (30.5). These higher days to squaring in
mid March sowing were due to low degree days accumulation in the months
of March and April than mid May sowing. The primary factor affecting crop
development is temperature as described by Hodges et al. (13). They also
observed that initiation of first square and its development was temperature
and cultivar dependant. They alongwith Reddy et al. (28, 29) further argued
that plant development rate is much increased at high temperature
shortening plant life period. Floral bud initiation and growth is affected by
photoperiod (2). Initiation of squaring was used by Godoy (10) for the
selection of early genotypes as against findings of Saleem et al. (32) which
revealed that appearance of first floral bud cannot be used as an indicator to
estimate earliness of cotton cultivars. Higher nitrogen level i.e 175 kg took
more number of days for floral bud initiation (35.0) and was statistically
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Table 2.
Effect of sowing date and nitrogen rates on earliness related traits of
cotton cultivars.
Treatments DFS DFF NAWF DFOB EI
Sowing dates
Mid March (S 1) 36.0a 63.7a 108.3 110.4a 48.3
Mid May (S 2) 30.5b 49.6b 99.4 91.1b 57.5
LSD (p=0.05) 3.49 4.59 NS 14.24 NS
Varieties
MNH-786 (non-Bt) 32.9 55.5 102.7 99.6 55.0
IR-1524 (Bt) 33.6 57.8 105.0 101.9 50.9
LSD (p=0.05) NS NS NS NS NS
N rates (kg/ha)
115 30.5b 50.1b 95.9b 93.1b 59.2a
145 34.2a 57.8a 106.8a 103.1a 51.1b
175 35.0a 62.1a 108.9a 106.0a 48.5b
LSD (p=0.05) 2.92 6.02 9.60 6.57
Means not sharing a common letter within a column differ significantly at 5% probability level.
NS= Non-significant, DFS= Days to first square, DFF= Days to first flower, NAWF= Node
above white flower, DFOB= Days to first open boll, EI=Earliness index (%),
similar to 145 kg N (34.2) (Table 2). Nitrogen level of 115 kg took minimum
number of days to floral bud initiation (30.5). The regression analysis
indicated that relationship between number of days to first floral bud initiation
and node above white flower was strong and positive (R 2 = 0.79) (Fig. 1a).
Similarly, linear regression coefficient (90 %) for number of days to first floral
bud initiation vs earliness index was even more higher indicating strong but
negative relationship (Fig 1b).
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Days to first flower
The results (Table 2) further indicated that number of days to first flower were
also affected by sowing dates and nitrogen levels significantly and by
cultivars non-significantly. Relatively less days to first flower were taken by
non-Bt cultivar MNH-786 (55.5) than Bt cultivar IR-1524 (57.8). Contrarily,
Rehana et al. (30) observed significant difference in cultivars for number of
days taken to open first flower. A cultivar taking less number of days to
flowering and first boll splition may be classified as earlier (9). Appearance of
first flower can be used as an indicator of early maturing cultivar (19). With
regard to sowing dates, mid March sowing took more days to appearance of
first flower (63.7) than mid May sowing (49.6). These higher days to flowering
in mid March sowing were due to low degree days accumulation in the
months of March and April than mid May sowing (Table 1). The primary
factor affecting crop development is temperature (13). Appearance of first
flower was photoperiod dependant (17) and plant growth rates are highly
correlated with temperature (38). The number of days from squaring to
flowering, as well as the days from flowering to boll opening were influenced
by temperature (12). Among N levels, 175 kg N took more number of days to
appearance of first flower (62.1) and was statistically at par with 145 kg N
(57.8). Relationship between number of days to appearance of first flower
and node above white flower was strong and positive (R 2 = 0.75) (Fig 2a).
Similarly its relation with earliness index was also strong and negative (R 2 =
0.80) (Fig. 2b).
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Days to node above white flower (NAWF)
This trait was significantly affected by nitrogen levels (Table 2) while sowing
dates and cultivars had non-significant effect. Relatively less days to node
above white flower were noted in mid May sowing (99.4) than in mid March
sowing (108.4) Similiar non-Bt cultivar MNH-786 showed relatively less days
to node above white flower (102.7) than Bt cultivar IR-1524 (105.0) (Table 2).
Waddle (37) was the first to use node above white flower as an indicator of
maturity in cotton. He reported that varieties that attain five NAWF were the
early maturing varieties. Nitrogen level of 175 kg took more days to node
above white flower (108.9) and was statistically at par with 145 kg N (106.8).
Nitrogen application after 175 kg did not respond indicating that high doses
of nitrogen did not increase the flowering period, days to node above white
flower and also seed cotton yield (16). Regression coefficient indicated that
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Comparison of Bt and non-Bt cotton cultivars for earliness indicators
343
dependence of earliness index on days to node above white flower was 77
percent which was strong and negative (Fig 3).
Days to first boll splition
Cultivars showed non-significant difference with respect to number of days
from planting to first boll splition (Table 2). Panhwar et al. (26) observed that
early maturing varieties opened their bolls earlier than late maturing varieties.
Days to open first boll was used for selecting the early genotypes by Godoy
(10). In contrast Rehana et al. (30) observed significant difference in cultivars
for number of days taken to open first boll. Mid March sowing took more
days to first boll splition (110.4) than mid May sowing (91.1). These higher
days in mid March sowing were due to low degree days accumulation in the
months of March and April than mid May sowing. Nitrogen rate of 175
kg resulted in more number of days to first boll splition (106.0) and was
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statistically similar to 145 kg N (103.1). Relationship between number of days
from planting to first boll splition and node above white flower was strong and
positive (R 2 = 0.69) (Fig. 4a). R 2 for number of days from planting to first boll
splition vs earliness index was even higher (87 %) but negative (Fig. 4b).
Earliness index (%)
Earliness index was affected by nitrogen levels while sowing dates, cultivars
and all interactions showed non-significant effect (Table 2). Nitrogen level of
115 kg showed significantly higher earliness index (59.2%) than 145 kg
(51.1%) and 175 kg N (48.5%). It indicated that increased N level increased
vegetative growth and delayed earliness. Similar results have also been
reported by earlier scientists (3, 33). Percentage of first picking in the multiple
harvests is a poor estimate of earliness (31).
CONCLUSION
It is concluded that mid May sowing and 115 kg nitrogen per hectare resulted
in more earliness. Cultivars showed non-significant effect on earliness related
parameters with relatively more earliness in non-Bt cultivar.
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