Effects of Date of Sowing on the Yield and Yield

Wheat Special Report No. 23a
Effects of Date of Sowing on the Yield
and Yield Components of Spring Wheat
and their Relationship with Solar Radiation
and Temperature at Ludhiana, Punjab, India
S.S. Dhillon and J.I. Ortiz-Monasterio R.
Wheat Special Report No. 23a
Effects of Date of Sowing on the Yield
and Yield Components of Spring Wheat
and their Relationship with Solar Radiation
and Temperature at Ludhiana, Punjab, India
s.s. Dhillon and J.1. Ortiz-Monasterio R.
November 1993
Contents
iv
Preface
iv
Acknowledgments
1
Introduction
3
3
Materials and Methods
Effect of genotype, planting date, and year on yield, yield components, and
phenology
,
Effect of PTQ, temperature, and solar radiation on yield and GM2 during
pre-anthesis
Absolute and relative losses with delayed sowing
3
4
7
7
8
12
13
Results and Discussion
Statistical analysis
,
Effect of genotype, planting date, and year on yield, yield components,
and phenology
Effect of PTQ, temperature, and solar radiation on yield and GM2 during
pre-anthesis
Effect of temperature and solar radiation during post-anthesis period on grain
yield and TGW
Use of the PTQ for explaining year effects
Absolute and relative losses with delayed sowing
13
Conclusions
14
References
15
16
17
18
Figure 1. Yield response of three spring wheat genotypes to seven dates of planting
Figure 2. Yield response over 4 years to seven dates of planting
Figure 3. GM2 response of three wheat genotypes to seven dates of planting
Figure 4. Changes in TGW and days to heading of three wheat genotypes over 4
years and seven dates of planting
Figure 5. Changes in days to maturity and grain-filling days of three wheat
genotypes over 4 years and seven dates of planting
Figure 6. Relationship between grain yield and PTQ2 and grain yield and mean
temperature in three wheat genotypes
Figure 7. Relationship between grain yield and solar radiation and grain yield and
GM2 in three wheat genotypes
Figure 8. Relationship between GM2 and PTQ2 and GM2 and mean temperature
(-20H to +lOH) in three wheat genotypes
Figure 9. Relationship between GM2 and solar radiation and yield and PTQ
(+ lOH to +40H) in three wheat genotypes
Figure 10. Relationship between grain yield and mean temperature (+ lOH to +40H)
and grain yield and solar radiation (+ lOH to +40H)
Figure 11. Relationship between grain yield and TGW and TGW and PTQ (+ lOH to
+40H) in three wheat genotypes
Figure 12. Relationship between TGW and mean temperature (+ lOH to +40H) and
TGW and solar radiation (+10H to +40H) in three wheat genotypes
Figure 13. Relationship between TGW and mean temperature (+ lOH to +40H)
over 4 years in three wheat genotypes
10
12
19
20
21
22
23
24
25
26
27
ii
Contents (continued)
28
29
30
Figure 14. Relationship between PTQ2 and yield and PTQ2 and GM2 over 4
years in three wheat genotypes
Figure 15. Changes in relative grain yield with different dates of heading (Julian)
in three wheat genotypes
Figure 16. Changes in relative GM2 with different dates of heading (Julian) in three
wheat genotypes
31
Appendix 1. Correlation coefficients for three genotypes between yield and GM2 vs
four different PTQ values during 7 years at Punjab Agricultural University in
Ludhiana, India
32
List of Wheat Special Reports
Note on Citing this Wheat Special Report
The information in this wheat special report is shared with the understanding that it is not
published in the sense of a refereed journal. Therefore, this report should not be cited in other
publications without the specific consent of E. Acevedo, CMP Subprogram Leader.
Correct Citation: Dhillon, S.S., and J.1. Ortiz-Monasterio R. 1993. Effects of Date of
Sowing on the Yield and Yield Components of Spring Wheat and their Relationship with
Solar Radiation and Temperature at Ludhiana, Punjab, India. Wheat Special Report No. 23a.
Mexico, D.F.: CIMMYT.
ISSN: 0187-7787
ISBN: 968-6923-14-4
AGROVOC descriptors: Triticum, spring crops, sowing time, date, genotype environment
interaction, yield factors, solar energy, temperature resistance, Punjab, Inda.
AGRIS category codes: F01; H50.
Dewey decimal classification: 631.53.
iii
Preface
This Wheat Special Report analyzes the effects of radiation and temperature on the date of
flowering and grain yield of spring bread wheat cropped under optimum conditions. The
experiments were conducted at Ludhiana, Punjab, India, over 7 years and using a range of
genotypes. The optimum flowering date for maximization of wheat grain yields is confirmed
to be when the ratio of radiation to temperature (PTQ) is at its maximum. The individual
effects of radiation and temperature on yield and yield components at various stages of crop
development are also examined.
We hope that the concepts validated here will be useful elements of wheat component
agronomy in the development of new spring wheat varieties and better agronomic practices
for wheat grown under irrigation (Mega-environment 1).
This short version (No. 23a) does not include the raw data that may be of interest to some
scientists. This information (Le., correlation coefficients for the three genotypes used in the
experiments, means averaged across reps, and climatic data) is provided in Appendices 2
through 5, which are included in No. 23b.
S.S. Dhillon is an agronomist with the Department of Plant Breeding, Punjab Agricultural
University, Ludhiana, India, and J.1. Ortiz-Monasterio R. is an agronomist, with the Wheat
Program, Crop Management and Physiology Subprogram, CIMMYT, Mexico.
E. Acevedo
Leader
Crop Management and Physiology Subprogram
CIMMYT Wheat Program
Acknowledgments
We wish to thank especially Dr. R.A. Fischer for his guidance and suggestions during data
analysis and Drs. E. Acevedo and K.D. Sayre for their discussions and suggestions on the
topic.
iv
Introduction
Wheat is the main cereal crop of the Indian Punjab. The main objectives of the India's
wheat production programs are to increase production to achieve self-sufficiency in food
grains, and to step up and establish production at a higher level. During 1965-66, wheat
acreage in India was 12.79 million hectares; this area increased to 24.0 million hectares
during 1991-92, an 88% increase. Wheat production for this same period increased from
10.7 million tons to 54.5 million tons, 409% increase. As shown in Table 1, yield
increases contributed significantly to the production increase.
Similarly, in the Punjab, while the area has doubled since 1965-66, production has
increased more than sixfold (Table 2). This is explained by the increase in yield from
1104 kglha in 1965-66 to 3715 kglha in 1990-91.
Table 1. Area, production, and yield or wheat in India rrom 1965 to 1992.
Year
1965-66
1970-71
1975-76
1980-81
1985-86
1990-91
1991-92
Area (000 ha)
Production (000 tons)
Yield (tll1a)
12.79
17.89
20.11
22.10
23.07
23.50
24.00
10.72
23.24
28.33
36.46
46.89
49.90
54.50
0.84
1.23
1.41
1.65
2.03
2.12
2.27
Table 2. Area, production and yield of wheat in Punjab from 1965 to 1991.
Year
1965-66
1970-71
1975-76
1980-81
1985-86
1990-91
Area
(000 ha)
Production
(000 tons)
Yield
(tll1a)
1548
2299
2449
2808
3113
3272
1916
5145
5809
7669
10992
12155
1.10
2.24
2.37
2.73
3.53
3.72
Intensive crop rotations have been widely adopted due to the availability of more
irrigation facilities. Wheat occupies a dominant place in double and multiple cropping
systems. Approximately 80% of the total cropped area during the rabi (winter) season in
Punjab is sown under wheat. Thus, wheat follows practically all kharif (summer) crops in
Punjab. The most common rotations involving wheat are:
1
Rice-Wheat
Cotton-Wheat
Maize-Wheat
Rice-Wheat-Sesbania (Green Manure)
MaizelRice-Potato-Wheat
Ground nut-Wheat
Rice- Pea-Wheat
Maize fodder- Brassica-Wheat
Khari f Pulses-Wheat
Depending upon the maturity and harvesting of the previous summer crop, the time of
sowing wheat is extended from the end of October to the end of December. Losses in
grain yield with delayed planting have been reported in Punjab (Randhawa et al. 1981).
The wheat crop is greatly influenced by temperature and radiation prevailing during the
season, particularly when water and nitrogen are not limiting. Nix (1976) showed that
temperature and radiation influence plant processes differently, but there combined effect
can be usefully described as a photothermal quotient (PTO). PTO is defined as the ratio
of daily total solar radiation in MJ/m 2/day divided by the mean daily temperature minus
4.5 0 C (base temperature). Midmore et al. (1984) and Fischer (1985) observed that
grains/m 2 (GM2) in wheat was associated with PTO over 30 days preceding anthesis.
Grain yield reductions with delayed sowing under optimal conditions of water and
nitrogen have been attributed to reduced GM2 caused by higher pre-anthesis
temperatures (Fischer and Maurer 1976) and to reduced thousand grain weight (TGW)
caused by higher post anthesis temperatures (Sofield et aJ. 1977, McDonald et aJ. 1983),
even though the irradiance levels also increased in each case. The wheat crop seems to be
source-limited during the pre-anthesis phase when GM2 is being determined--particularly
during the phase of rapid spike growth and development, which occurs 20 to 30 days
prior to anthesis.
It has been demonstrated that the number of grains is determined by the carbohydrate
supply to the crop during this phase. Specifically, it has been estimated that 10 mg of
carbohydrates directed to the growing spike are required during rapid spike growth to
keep a potential grain from aborting (Fischer 1984), for wheat crops that do not suffer
from nutrient or water stress and without competition from weed, diseases, and pests. The
theory behind the PTO is based on the assumption that radiation (assuming close to full
light interception) and temperature are the driving forces in assimilate production and
development rate, respectively, during this critical phase. High radiation values, through
a larger assimilate production and low temperatures, by extending the crop duration
during this critical phase. Therefore, high PTO values should result in a larger number of
GM2. Fischer (1985) specifically applied the PTO concept to explain the effects of
radiation and temperature on kernel number in wheat crops. He confirmed that dry matter
accumulation under conditions at Ciudad Obregon, Sonora, Mexico (January to March)
was linearly related to absorbed photosynthetic radiation (slope of 3 g/MJ PARA; PARA
= 0.45 * incident solar radiation for full ground cover). He also inferred mainly from the
literature that rate of development during the terminal spikelet to anthesis period was
linear with respect to average temperature (max + minl2) minus a base temperature of
4.S°C.
The PrO was calculated on a daily basis with the following algorithm:
if T mean> 10
PrO= solar radiation/«max + min)/2)
ifT mean <= 4.5
PrO= 0
if 4.5 < T mean <=10 PrO= solar radiation * 1/5.5* «T-4.5)/5.5)
2
The last relationship means that, for a given solar radiation, maximum PTQ is reached at
T mean = 10, but PTQ rapidly and linearly drops to zero at T mean =4.5.
The field studies in Ludhiana were undertaken from 1985-86 to 1991-92 with three
objectives:
• To find the optimum planting date for wheat in the Punjab.
• To find the absolute and relative losses in grain yield, GM2 and TGW, with
delay in sowing from the optimum time.
• Understand the first two objectives in terms of the effect of temperature and
radiation combined and separately on yield, GM2, and TGW.
Materials and Methods
Field experiments were conducted from 1985 through 1992 on a loamy sand soil at
Punjab Agricultural University, Ludhiana. Ludhiana is situated at 30 0 54' N latitude and
75 0 48' E longitude and 247 mas!. Sixty-six genotypes having spring growth habit and ten
dates of planting were studied, although not all genotypes and planting dates were studied
each year. The genotypes and planting dates sown each year are given in Table 3. The
plots were managed under optimal conditions of fertilizer and irrigation. Broad leaf and
other grassy weeds were completely controlled by hand hoeing. The net plot area
harvested for each genotype was 7.36 m 2 in each year. The seeding density used in all
genotypes, planting dates, and years was 100 kglha. Heading date was defined as the date
when about 75% of the spikes had fully emerged from the boot and maturity date when
100% of the spikes were without green color. GM2 was calculated from grain yield and
TGW. The treatment design was a factorial combination of planting dates and genotypes
arranged as a split-plot design with three replications. Main plots were planting dates and
subplots were genotypes.
Effect of genotype, planting date, and year on yield, yield components,
and phenology
The statistical analysis was done first by years for all the planting dates and genotypes.
Then a combined analysis of an orthogonal subset of data was done for 4 years (1987-88,
1988-89, 1989-90, and 1991-92), three replications, three genotypes [PBW 34 (long
season), PBW 154 (medium season) and PBW 226 (medium to short season)], and seven
planting dates (Oct. 25, Nov. 5, Nov. 15, Nov. 25, Dec. 5, Dec. 15, and Dec. 25) to study
the interactions of genotype x year, planting date x year and genotype x planting date x
year. Replications and experiments were considered as random effects and genotype and
planting dates as fixed effects.
Effect of PTQ, temperature, and solar radiation on yield and GM2 during the
pre-anthesis period
To evaluate the effect of temperature and radiation on yield, GM2, and TGW, the
complete data set (all years and dates) of the selected genotypes was used. Weather
variables, such as temperature, radiation, etc., were recorded at a weather station less than
1 km from the experimental plots. The following PrQs were generated by calculating the
daily PTQ and averaging them for different periods:
PTQ1: -30 days to heading,
PTQ2: From -20 days to heading to +10 days after heading,
PTQ3: -20 days to heading,
3
PTQ4: From -20 days to heading to +20 days after heading,
PTQ TGW: From heading +10 days to heading +40 days.
The PTQs were expressed as MJ/m 2/dayf'C. The correlations between PTQs for the
above periods and yield and GM2 are given in Appendix 1. Out of the four PTQs, PTQ2
calculated in the pre-heading phase was more consistent for predicting GM2 and was
selected for further use. The post-anthesis photothermal quotient (PTQ TGW), calculated
from heading +10 to heading +40 days period, was used with TGW.
Absolute and relative losses with delayed sowing
To calculate the absolute and relative losses caused by delayed planting date, only data
from the optimum planting date to 25DEC were used. The optimum planting dates were
05NOV for PBW34 and NOV15 for PBW154 and PBW 226. Then absolute and relative
losses were calculated from that date to 25DEC for all three genotypes. The 25DEC date
was selected because there are basically no farmers planting beyond this planting date.
Data from a different number of years were available for each genotype; PBW 34
(average of 6 years) PBW 154, (average of 7 years), and PBW 226 (average of 5 years).
The method of analysis to estimate yield losses due to delays in planting date was done
with the following regression functions:
Yi
=a
In(Yi)
+ bPDi + u
absolute
(1)
=a
relative
(2 )
+ bPDi + u
where Yi is the yield in kg/ha of planting date i, In(Y j) is the natural log of Y i' and PDi is
the Julian date for the planting date i. The linear speCification (function 1) provides an
estimate of the yield reduction due to delays in planting dates in absolute terms (Le., b
measures kg/halday yield loss) while the logarithmic specification in function (2) gives
the relative yield reduction (i.e., 100 (dq/dVi)ri =100b measures the percent per day
yield loss) (Gujarati 1988).
Table 3. Detail of genotypes and planting dates used in the experiments from 198586 to 1991-92.
Exp.
Julian
Calendar
1
1985-86
Genotypes
Sowing Dates
Year
288
298
308
318
328
338
348
358
5
15
150cr
250cr
05NOV
15NOV
25NOV
05DEC
15DEC
25DEC
05JAN
15JAN
4
WL711
PBW34
PBW 120
PBW54
PBW 138
PBW 154
PBW 159
PBW 179
PBW 181
SKAMLI
HD2285
TL1210
Table 3. Continued.
Exp.
Calendar
2
1986-87
Genotypes
Sowing Dates
Year
Julian
150cr
250cr
05NOV
15NOV
25NOV
050EC
150EC
250EC
05JAN
15JAN
288
298
308
318
328
338
348
358
5
15
WL 711
PBW 120
PBW 138
PBW 154
PBW 188
PBW 189
PBW34
PBW 206
SKAMLI
WL 711
PBW 154
PBW 222
PBW 226
PBW 230
SKAMLI
PBW34
POW 212
TL2603
WL 1562
PBW 222
PBW 226
POW215
POW 218
HO 2329
HO 2428
PBW 138
PBW 154
PBW34
3
1987-88
150cr
25NOV.
05NOV
15NOV
25NOV
050EC
150EC
250EC
288
298
308
318
328
338
348
358
4
1988·89
250cr
05NOV.
15NOV
25NOV
050EC
150EC
250EC
298
308
318
328
338
348
358
5
1989-90
150CT
25OCT
05NOV
15NOV
25NOV
050EC
150EC
250EC
288
298
308
318
328
338
348
358
PBW 154
PBW222
PBW226
POW 215
PBW34
HO 2329
POW 220
6
1990·91
200CT
25 OCT
05NOV
15NOV
25NOV
050EC
150EC
293
298
308
318
328
338
348
PBW 154
PBW222
PBW226
POW 215
POW 225
POW 227
HD 2329
5
Table 3. Continued.
Exp.
Year
Sowing Dates
Calendar
7. 1991-92
Genotypes
Julian
25DEC
05JAN
358
5
200CT
250CT
05NOV
15NOV
25NOV
05DEC
15DEC
3004
25DEC
05JAN
293
298
308
318
328
338
348
PBW 154
PBW 222
PBW 138
PBW 226
HD 2329
HD 2285
CPAN
358
5
WH542
POW 215
POW 233
PBW 234
PBW34
Table 4 shows a summary of the climatic data for the years of this study. The year 198889 had the lowest mean temperatures for the months of January and February compared
to other years. The solar radiation during February was the highest 18.05 MJ/m 2 in 198889 and the lowest 11.13 MJ/m 2 in 1989-90. There was not much variation in other
months of the various years under study except that in 1988 April was the hottest both for
maximum and minimum temperatures. The year 1988-89 can be considered climatically
as the better year among all given the low temperatures and high radiation levels in the
pre-anthesis phase, as shown by the PTQ values in the month of February.
Table 4. Maximum, minimum, solar radiation, and PTQ values for Ludhiana, India
(30° 54') for the wheat seasons studied.
Year
Oct.
Nov.
Dec.
Jan.
Feb.
March
April
21.2
19.5
21.6
21.1
18.8
20.2
20.0
18.8
19.6
19.5
17.7
19.7
18.3
17.7
20.4
22.9
22.8
20.7
19.7
21.2
19.7
25.3
26.8
26.1
33.4
34.9
36.1
32.9
34.2
31.9
33.1
Maximum temperature (0C)
1985-86
1986-87
1987-88
1988-89
1989-90
1990-91
1991-92
29.9
30.4
32.2
31.8
32.8
30.7
31.8
26.2
26.6
27.8
26.5
26.1
26.9
26.0
6
~6.2
.24.6
25.8
25.3
Table 4. Continued.
Year
Oct.
Nov.
Dec.
Jan.
Feb.
March
April
:0.1
11.7
10.1
11.7
11.6
11.5
10.1
8.2
6.1
6.0
7.1
7.6
7.4
7.6
4.2
5.7
6.4
4.8
7.7
5.3
7.2
6.4
9.1
7.8
6.3
9.3
8.6
7.4
11.6
12.8
12.3
11.5
11.2
12.0
11.8
17.2
17.7
17.9
15.2
16.8
16.2
16.8
17.17
16.39
16.28
17.74
16.67
13.31
11.99
13.97
12.81
13.15
15.42
12.06
10.34
11.40
11.64
10.42
9.36
9.42
8.98
12.52
11.14
11.69
11.55
11.22
12.17
8.47
14.05
14.48
15.87
18.05
11.13
13.25
13.23
19.41
17.31
18.62
18.78
18.49
16.92
15.45
23.36
22.39
21.95
24.46
22.88
19.97
16.58
1.08
1.48
1.28
1.10
1.05
1.01
1.02
1.77
1.39
1.44
1.72
1.23
1.60
1.12
1.56
1.28
1.52
2.18
1.17
1.37
1.56
1.42
1.14
1.30
1.36
1.48
1.20
1.15
1.15
1.06
0.98
1.30
1.11
1.04
0.84
Minimum temperature (0C)
1985-86
1986-87
1987-88
1988-89
1989-90
1990-91
1991-92
17.1
16.8
18.1
16.2
16.0
16.4
15.0
Solar radiation (MJ/m 2)
1985-86
1986-87
1987-88
1988-89
1989-90
1990-91
1991-92
PTQ (MJ/M1Jday/°C)
1985-86
1986-87
1987-88
1988-89
1989-90
1990-91
1991-92
0.91
0.87
0.81
0.91
0.84
0.99
0.83
0.98
0.90
0.93
0.82
0.90
Results and Discussion
Statistical analysis
The statistical analysis of individual years for yield, GM2, and TGW revealed that
sowing dates and genotypes had significant effect on yield and yield components in all
the years (Table 5). However, the interaction between sowing dates and genotypes was
not significant for yield in three years (1985-86, 1986-87, and 1991-92) and GM2 in 2
years (1987-88 and 1990-91).
The combined analysis of the orthogonal subset of data for four years, three genotypes
and seven planting dates revealed that planting date x genotype interactions were
significant for yield and GM2 (Table 6). Also the year x planting date interaction was
significant for grain yield. The year x planting date x genotype interaction was significant
7
Table 5. Statistical analysis by years for yield, GM2, and TGW.
Year
1985-86
Yield (kglha)
GM2
TGW (g)
SEb a
Dates
Genotype
Date x
Genotype
••
••
••
••
••
••
••
••
211.91
534.91
0.570
12.04
12.08
2.49
••
CV%
1986-87
Yield
GM2
TGW
.*
*.
*.
**
••
.*
**
**
205.16
517.70
0.595
10.81
10.82
2.61
1987-88
Yield
GM2
TGW
••
*
••
.*
**
**
NS
NS
218.76
561.16
0.582
10.46
11.15
2.40
Yield
GM2
TGW
**
-
NS
••
.*
-*
-*
311.42
693.39
0.612
11.64
11.77
2.34
Yield
GM2
TGW
**
**
**
**
**
**
191.31
466.29
0.629
8.77
9.16
2.54
Yield
GM2
TGW
.*
**
**
**
**
NS
NS
**
220.61
541.77
0.669
10.88
11.38
2.75
Yield
GM2
TGW
**
*
**
**
**
**
.*
*
**
302.97
777.71
0.606
12.80
13.05
2.62
1988-89
1989-90
1990-91
1991-92
... Significant at P «
••
_.
**
**
**
•
••
**
=0.05); ** Significant at P « =0.01); NS =nonsignificant.
a Standard error of the difference between two means for comparison of two subplot means at the same
main plot level.
for TGW, days to heading (Days H), days to maturity (Days M), and grain-filling days
(Days H-M).
Effect of genotype, planting date and year on yield, yield components,
and phenology
Yield--As the combined analysis shows, the three-way interaction between year, planting
date, and genotype was not significant. This suggests that the genotype by planting date
interaction, which was significant, was independent of the year effect. The mean grain
yield across years at the earliest planting date (250CI) was 4354, 4505, and 4133 kglha
for PBW 34, PBW 154, and PBW 226, respectively. By delaying the planting date to
05NOV and 15NOV, the yield of all three genotypes improved except for PBW 34,
which produced the highest yield on the 05NOV planting date (Figure 1). The 15NOV
8
Table 6. Combined analysis of orthogonal subset of data 4 years, three replications,
three genotypes, and seven planting dates.
Source of variation
Y
Rep(Y)
Planting date
Y x P date
Y x rep x P date
Genotype
Y x genotype
P date x genotype
Y x P date x genotype
Error
Standard error'l
*
df
(kglha)
3
8
6
18
48
2
6
12
36
112
Yield
(g)
GM2 TGW Days
H
Days
M
Days
H-M
**
NS
**
**
*
**
**
**
**
NS
**
**
**
**
**
**
**
**
**
**
NS
NS
NS
**
**
**
**
*
**
**
**
**
**
**
NS
NS
NS
**
**
**
**
**
136
415
1.42
1.80
0.64 1
1.80
significant at P « = 0.05); ** significant at P « = 0.01); NS non significant
a Standard error of the difference between two means for comparison of two subplot
means at the same main plot level.
planting date produced the highest yield for paw 226 (5050 kg/ha) followed by paw
154 (4744 kg/ha) and paw 34 (4138 kg/ha). With further delay in planting date, the
yield of all the three genotypes decreased. However, the rate of reduction was more
severe in paw 34 compared to PBW 154 and PBW 226 (Figure 1). Therefore, the
genotype by planting date interaction can be explained by the earlier optimum planting
date of PBW34 as well as the faster decline in yield of this genotype compared to
PBW154 and PBW 226. A significant interaction for yield between years and planting
date revealed that 1988-89 was the highest yield year for all genotypes at all the planting
dates except 25DEC. At this planting date, 1991-92 produced 3502 kglha compared to
3351 kglha in 1988-89 (Figure 2). As mentioned before, 1988-89 had the lowest
temperature and the highest radiation and PrQ in the pre-anthesis period.
Yield componenls--The response of GM2 was very similar to that of yield, in contrast to
TGW. The three-way interaction for GM2, between year, planting date, and genotype
was not significant. However, the genotype by planting date interaction was significant.
The number of GM2 for all three genotypes, averaged across the years under different
planting dates, had a similar trend to that of yield, which shows the predominant role of
GM2 in determining final yield (Figure 3). For TGW, the genotype by planting date
interaction also interacted with year. TGW for all three genotypes decreased with any
delay in planting date after 150CT in all the years (Figure 4a). However, among years,
1988-89 produced heavier grains compared to others in all genotypes at almost all
planting dates. In addition, 1987-88 had a different pattern of TGW reduction with delays
in planting date compared to the other years. The ranges ofTGW across years and dates
were 45-56, 44-52, and 44-48g for PBW 34, PBW 154, and PBW 226, respectively.
Phenology--The interaction between genotype, planting date, and year was significant for
days to heading, days to maturity, and grain-filling days. The ranges of number of days to
9
headi ng across years and dates were 99-111, 90-100, and 88-93 for PBW 34, PBW 154,
and PBW 226, respectively (Figure 4b). It is also clear from the data that PBW 34 took
the maximum days to heading when planted on 250cr; for the other two genotypes, the
maximum was reached usually on 15NOV. The number of days to heading was reduced
with further delays in sowing in all the genotypes. The number of days to maturity were
drastically reduced with any delay in planting after 150cr for all three genotypes and in
all four years (Figure Sa). In general, the number of grain-filling days was reduced with
any delay in planting date for all genotypes, however, for PBW 34 the rate of reduction
was slower than for the other two genotypes (Figure 5b). Undoubtedly, PBW34 reached
heading later than the other genotypes in early plantings. The steadily increasing
maximum and minimum temperatures (Table 4) during February, March, and April may
have caused the late planting date to produce lower number of GM2, lower TGW, and
ultimately lower yields. Radiation increases should, however, have compensated to some
extent for the increase in temperature. The next section examines these relationships.
Effect ofPTQ, temperature, and solar radiation on yield and GM2 during the preanthesis period
Effect on grain yie/d--Grain yield across planting dates was linearly and positively
correlated with the pre-anthesis photothermal quotient (-20 H to +10 H) for all three
genotypes (Figure 6a). The correlation coefficient values were 0.95, 0.70, and 0.64 for
PBW 34, PBW 154, and PBW 226, respectively, including all points in the graph.
Generally, grain yield increased with the increase in PTO values--except in the 15JAN
late planting in genotypes PBW 34 and PBW 154 (there was no 15JAN planting for PBW
226) where the PTO values were relatively high, but grain yield was not. It is believed
that in the 15JAN planting the crops were exposed to high temperatures around meiosis
and anthesis causing spike sterility, resulting in a lower number of GM2 and, in turn,
yield for a given PTO value. The other possible explanation is that, in the 15JAN
planting, PBW34 and PBW 154 did not reach full light interception, therefore they could
not efficiently use the available radiation. Thus, although PTO values were relatively
high, yield and GM2 were low. The effect of temperature during the pre-anthesis period
(-20 H to +10 H) was found to be negatively correlated with yield across planting dates
for all the genotypes, PBW 34 (r = -0.92), PBW 154 (r = -0.86), and PBW 226 (r = -0.86)
(Figure 6b). Similarly, yield was also found to be negatively correlated with solar
radiation during the pre-anthesis period for PBW 34 (r = -0.86), PBW 154 (r = -0.71),
and PBW 226 (r = -0.40) (Figure 7a). PBW 34 was found to be relatively more sensitive
to higher temperature and solar radiation conditions. We would expect solar radiation to
be positively correlated with yield, however, due to the high autocorrelation between
solar radiation and temperature, this correlation becomes negative (Table 7).
Effect on GM2--For all three genotypes, GM2 was positively correlated with grain yield
across planting dates. The correlation coefficients (r) were 0.97,0.97, and 0.84 for PBW
34, PBW 154, and PBW 226, respectively (Figure 7b). GM2 was positively correlated
with PTO during the pre-anthesis period (-20 H to +10 H). The number of GM2 ranged
from 3790 to 11,550 and PTOs from 1.08 to 1.58 MJ/m 2/dayPC. The correlation
coefficients (r) were 0.89,0.72, and 0.94 for PBW 34, PBW 154, and PBW 226,
respectively (Figure 8a). GM2 increased as PTO increased, except for the 15JAN
planting. See the above explanation on yield.
GM2 was negatively correlated with mean temperature during the pre-anthesis period (20 H to +10 H) for all three genotypes, PBW34 (r=-0.81), PBW154 (r=-0.73), and PBW
226 (r -0.48) (Figure 8b).
=
The number of grains were also negatively correlated with solar radiation during the preanthesis (-20 H to +10 H) period, for PBW 34 (r = -0.73), and PBW 154 (r =-0.55).
10
Table 7. Correlation using values averaged across year for yield, yield components, and climatic
variables in three genotypes.
PBW34
Days
Days
Yield
GM2
TGW
MTIGW
RADTGW
PTQTGW
MTGM2
RADGM2
PTQ2
1.000
-0.953
-0.868
-0.994
0.991
0.963
-0.985
0.990
0.954
-0.943
Yield
1.000
0.971
0.938
-0.907
·0.852
0.896
-0.924
-0.855
0.949
GM2
1.000
0.834
-0.797
-0.719
0.787
-0.814
-0.730
0.885
TGW
MTIGW
1.000
-0.991
-0.968
0.985
-0.992
-0.959
0.939
1.000
0.988
-0.992
0.995
0.972
-0.920
RADTGW PTQTGW
1.000
-0.969
0.985
0.981
-0.878
1.000
-0.982
-0.965
0.898
MTGM2 RADGM2 PTQ2
1.000
0.975
-0.930
1.000
-0.826
1.000
PBW 154
Days
Days
Yield
GM2
TGW
MTIGW
RADTGW
PTQTGW
MTGM2
RADGM2
PTQ2
1.000
-0.849
-0.721
-0.973
0.991
0.976
-0.963
0.970
0.961
-0.386
Yield
1.000
0.974
0.919
-0.781
-0.731
0.706
-0.862
-0.709
0.703
GM2
1.000
0.811
-0.634
-0.576
0.538
-0.727
-0.547 .
0.717
TGW
1.000
-0.951
-0.928
0.918
-0.974
-0.921
0.501
MTIGW
1.000
0.994
-0.988
0.962
0.986
-0.294
RADTGW PTQTGW
1.000
-0.986
0.942
0.996
-0.213
1.000
-0.947
-0.987
0.248
MTGM2 RADGM2 PTQ2
1.000
0.940
-0.512
1.000
-0.194
1.000
PBW 226
Days
Days
Yield
GM2
TGW
MTTGW
RADTGW
PTQTGW
MTGM2
RADGM2
PTQ2
1.000
-0.587
-0.067
-0.992
0.987
0.899
-0.658
0.847
0.902
0.187
Yield
1.000
0.841
0.601
-0.516
-0.214
0.770
-0.858
-0.397
0.637
GM2
1.000
0.076
0.026
0.332
0.454
-0.476
0.147
0.936
TGW
1.000
-0.993
-0.882
0.735
-0.876
-0.933
-0.196
MTTGW
1.000
0.924
-0.686
0.836
0.956
0.291
RADTGW PTQTGW
1.000
-0.386
0.607
0.912
0.539
1.000
-0.886
-0.695
0.181
MTGM2 RADGM2 PTQ2
1.000
0.783
-0.224
1.000
0.426
Note: Ten planting dates used in the correlation for PBW 34 and PBW 154 and nine planting dates used (150Cf to 05JAN) for
correlations of PBW 226.
11
1.000
However, in the case of PBW 226, the number of grains was not much affected by
changes in solar radiation (r = 0015), so PBW 226 was found to be relatively more
tolerant to the changes in temperature and solar radiation compared to PBW 154 and
PBW 340 Solar radiation was expected to have a positive effect on GM20 However, due
to the high correlation between temperature and radiation, i.e., 0.98, 0.94, and 0.78 for
PBW 34, PBW 154, and PBW 226, respectively (temperature having a negative
relationship with GM2, Table 7), there was a negative relationship between solar
radiation and GM2 in two of the genotypes studied (Figure 9a).
The above analysis shows that GM2 is affected by both solar radiation and temperature
during the pre-anthesis period. This can be observed by the improvement in the
relationship between GM2 and PTQ (which uses both solar radiation and temperature)
when compared to either solar radiation or temperature alone.
Effect of temperature and solar radiation during the post-anthesis period on grain
yield and TGW
Effect on grain yield--For all three genotypes, grain yield across planting date means was
positively and linearly correlated with the combined effect of temperature and solar
radiation (PTQ) during the post-anthesis period (+ 10 H to +40 H). The correlation was
stronger for PBW 34 (r = 0.90) than for PBW 154 (r = 0.71) and PBW 226 (r = 0.77)
(Figure 9b). Grain yields ranged from 1393 to 4356 kg/ha, 1545 to 4555 kg/ha, and 2933
to 4905 kg/ha with the corresponding ranges in PTQ values from 1.08 to 1.43, 1.09 to
1.50, and 1.00 to 1.55 for PBW 34, PBW 154, and paw 226, respectively.
The increasing mean temperature during the post-anthesis period had a strong effect on
grain yield. The yield of all three genotypes decreased with an increase in mean
temperature. However, increasing mean temperature had more a negative effect on yield
for paw 34 (r = -0.91) compared to PBW 154 (r = -0.78) and PBW 226 (r=-0.52)
(Figure lOa). Similarly, the grain yield of PBW 34 was more severely affected by
increasing solar radiation during the post-anthesis period (H+ 10 to H+40) (r = -0.86)
compared to paw 154 (r = -0.73) and paw 226 (r = -0.21) (Figure lOb). PBW 226 and
paw 154, being short and mid-season genotypes, were found to be relatively more
tolerant to increases in mean temperature and solar radiation conditions during the postanthesis period.
Effect on TGW--Grain yield was positively correlated with TGW for all three genotypes
(Figure 11a): paw 34 (r =0.94), paw 154 (r =0.92), and paw 226 (r = 0.60). In PBW
34, TGW was found to be positively correlated with the photothermal quotient during the
post-anthesis period (H +10 to H +40), however, it was highly negatively correlated with
the separate effect of temperature and solar radi ation; the correlation coefficient (r)
values were 0.99, -0.99, and -0.97 for TGW vs PTQ, mean temperature, and mean
radiation, respectively. A similar trend was observed in PBW 154 and paw 226. The
correlation coefficient (r) values were 0.92, -0.95, and -0.93, for TGW vs PTQ, mean
temperature, and solar radiation for paw 154 and 0.74, -0.99, and -0.88 for paw 226,
respectively (Figures lib, 12&, 12b). The best correlations with TGW occurred with
mean temperature, without any improvement by adding radiation alone or together with
mean temperature (PTQTGW), suggesting that TGW is solely affected by temperature
under Ludhiana conditions. When the relationship between TGW and mean temperature
was plotted by year, we can still observe a strong relationship between these two factors
(Figure 13).
Use of the PTQ for explaining year effects
PTQ was useful in explaining part of the year x planting date variability in yield and
GM2. Although the correlations were not as high as with date of planting means, the
12
values are significant and demonstrate how variability among years can also be explained
by PTQ. This can be seen in Figures 14a and 14b where the year 1988-89 had higher
PTQ values with correspondingly higher GM2 and yield values. The higher variability
observed by using the yearly data could be explained by soil differences over the years.
Absolute and relative losses with delayed sowing
The grain yield of all three genotypes decreased with a delay in sowing. However, the
optimum date varied with the genotype. Calculating for delays after the optimum date,
grain yields decreased at rates of 41,35, and 36 kg/ha/day for PBW 34, PBW 154, and
PBW 226, respectively; the corresponding values on a relative basis for these genotypes
were 1.2,0.9, and 0.9%/ha/day.
With a delay in sowing from 05NOV to 25DEC for PBW 34 and from 15NOV to 25DEC
for PBW 154 and PBW 226, GM2 on an absolute basis decreased at a rate of 61,58, and
56/day for PBW 34, PBW 154, and PBW 226, respectively, and the corresponding values
were 0.8, 0.6, and 0.5%/day on a relative basis for PBW 34, PBW 154, and PBW 226.
For PBW 34, the number of GM2 decreased at the rate of 749 grains/m 2pC with an
increase in mean temperature from 14.50 to 18.45 0 C during the pre-anthesis period (-20
H to +10H). The number of grains decreased at the rate of 599 grains/m 2PC and
554/grains/m 2PC with increases in mean temperatures from 14.35 to 18.17 0 C and from
13.76 to 17.700 C for PBW 154 and PBW 226, respectively.
With a delay in sowing from 05NOV to 25DEC for PBW 34 and from 15NOV to 25DEC
for PBW 154 and PBW 226, TGW was reduced at rates of 0.18,0.13, and 0.13 glday of
planting delay for PBW 34, PBW 154, and PBW 226, respectively. On a relative basis,
the values were 0.4, 0.3, and 0.3%/day for PBW 34, PBW 154, and PBW 226,
respectively.
For PBW 34, TGW was reduced at a rate of 1.52 g;Oc with a corresponding increase in
mean temperature from 18.70 to 24.52 0 C during the post-anthesis period (H+ 10 to
H+40). For PBW 154, TGW decreased at a rate of 1.03 g;Oc with a corresponding
increase in mean temperature from 18.47 to 23.68 0 C during the post-anthesis period.
Similarly, for PBW 226, TGW was reduced at a rate of 1.05 gjOc with a corresponding
increase in mean temperature from 17.26 to 22.23 0 C.
Conclusions
The results of these studies suggest that time of sowing is a very important factor for
determining yield. The optimum planting dates were 05NOV for PBW 34 and 15NOV
for PBW154 and PBW 226. Delay in sowing beyond these dates caused severe
reductions in GM2, TGW, and yield. High post-anthesis temperatures had a highly
negative effect on TGW and yield on all genotypes.
All three genotypes maximized their yield when the PTQ value was highest between 20
days before heading to 10 days after heading. This suggests that all genotypes should
maximize their yield by flowering during the highest PTQ in the growing season. PBW
34 is a longer season genotype compared to the other two and the highest PTQ value
occurs at a given time during the year. Therefore, PBW 34 will have to be planted earlier
than the other two so that all three genotypes flower at about the same time to take
advantage of the high PTQ values. It can be seen clearly that this was the case for PBW
34 and PBW 154 (Figure 15). However, that did not hold true for PBW 226 (shortseason genotype).
13
If we analyze GM2, we can observe that PBW 34 and PBW 154 have a period of 10 days
(between Julian dates 50 and 60--about 20 and 28 Feb.) when GM2 is maximized
(Figure 16). However, for PBW 226 the optimum is around Julian date 40 (Feb. 10) and
then there is a sharp drop after this date. This may be explained by a possible inability of
PBW 226 to reach full light interception after Julian date 40.
GM2 could be better explained by the combination of solar radiation and temperature
(PTQ2) than by either of the two alone during the pre-anthesis phase, while TGW could
be better explained only by temperature in the post-anthesis phase.
These results suggest that it would be useful to look at long-term climatic data and
calculate probabilities of when the highest PTQ occurs and use that as the target optimum
flowering date from which the optimum planting date could be calculated.
The PTQ2 pre-anthesis seems to be able to predict which will be high yielding years.
There is a 1.2, 0.9, and 0.9%/ha/day yield loss after the optimum planting date for PBW
34 (long season), PBW 154 (medium season), and PBW 226 (short season), respectively.
References
Fischer, R.A. 1984. Physiological limitations to producing wheat in semitropical and
tropical environments and possible selection criteria. In pages 209-230, Wheat for More
Tropical Environments, A Proceedings of the International Symposium, Sept. 24-28,
1984. Mexico, D.F.: CIMMYT.
Fischer, R.A. 1985. Number of kernels in wheat crops and the influence of solar radiation
and temperature. J. Agric. Sci. 105:447-61.
Fischer, R.A., and R. Maurer. 1976. Crop temperature modification and yield potential in
a spring wheat. Crop Sci. 16:855-9.
Gujarati, D.M. 1988. Basic Econometrics. Second Edition. Mc Graw-Hill Book
Company.
McDonald, G.K., B.G. Sutton, and F.W. Ellison. 1983. The effects of time of sowing on
the grain yield of irrigated wheat in the Namoy Valley, New South Wales. Aust. J. Agric.
Res. 34:229-40.
Midmore, DJ., P.M. Cartwright, and R.A. Fischer. 1984. Wheat in tropical
environments. II. Crop growth and grain yield. Field Crops Res. 8:207-27.
Nix, M.A. 1976. Climate and crop productivity in Australia. In pages 495-507, S.
Yoshida, ed., Climate and Rice. Int. Rice Res. Inst., Los Banos, Philippines.
Randhawa, A.S., S.S. Dhillon, and W. Singh. 1981. Productivity of wheat varieties, as
influenced by the time of sowing. J. Res. Punjab Agric. Univ. 18(3):227-33.
Sofield, G., L.T. Evans, M.G. Cook, and G.F. Wardlaw. 1977. Factors influencing the
rate and duration of grain-filling in wheat. Aust. J. Plant Physio\. 4:785-97.
14
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Figure 1. Yield response of three spring wheat genotypes to seven dates of planting.
15
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Figure 2. Yield response over 4 years to seven dates of planting.
16
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Figure 3. GM2 response of three wheat genotypes to seven dates of planting.
17
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Figure 4. Changes in TGW and days to heading of three wheat genotypes over 4
years and seven dates of planting.
18
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Plonting Date
Plonting Date
Figure S. Changes in days to maturity and grain-filling days of three wheat
genotypes over 4 years and seven dates of planting.
19
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ME',L\I\j TEMF' -20H
PTQ2 (MJ/M2/DAY/ C)
-
20
+ IOH ( C)
Figure 6. Relationship between grain yield and PTQ2 and grain yield and mean
temperature in three wheat genotypes.
20
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20
RADIATION - 20H +10H
2000
1000
2000400060008000100002000
GM2
(MJ/M2/DAY/ C)
FIgure 7. Relationship between grain yield and solar radiation and grain yield and
GM2 in three wheat genotypes.
21
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10
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12
14
16
18
20
MEAN TEMPERATURE ( C)
PTQ2 (MJ/M2/DAY/ C)
Figure 8. Relationship between GM% and PTQ% and GM% aDd mean temperature (%OH to +1011) in three wheat genotypes.
22
6000
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10
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14
16
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20
PTa
+ 1 0 H +40H
(MJ/M2/DAY/ C)
RADIATION (MJ/M2/DAY)
Figure 9. Relationship between GM2 and solar radiation and yield and PTQ (+10 to
+40) In three wheat genotypes.
23
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RADIATION + 1OH +40H
12 14 16 18 20 22 24 26 28
MEAN TEMP + 10H +40H ( C)
(MJ/M2/DAY)
Figure 10. Relationship between grain yield and mean temperature (+108 to +408)
and grain yield and solar radiation (+108 to +408).
24
6(',('0
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TGW (g)
PTQTGW (MJ/M2/DAY/ C)
Figure 11. Relationship between grain yield and TGW and TGW and PTQ (+108 to
+408) in three wheat genotypes.
2S
55
55 I
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RADIATION (MJ/M2/DAY/ C)
MEAN TEMPERATURE ( C)
Figure 11. Relationship between TGW and mean temperature (+108 to +4(8) and
TGW and solar radiation (+108 to +408) in three wheat geROtypes.
26
60
••
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55
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MEAN TEMP + 10H +40H
Figure 13. Relatioashlp betweeD TGW aDd
meaD temperature (+118 to +408) over 4
years iD three wheat aeDOtypes.
27
7000
6000
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2.0
PTQ2 (MJ/M2/DAY/ C)
PTQ2 (MJ/M2/DAY/ C)
Figure 14. Relationship between PTQ2 and yield and PTQ2 and GM2 over 4 years
in three wheat genotypes.
28
-
-
EJ O
0
-
-
,..., c::
L.->
110
,----,----,--------,---,--------r----r---,------,------,
100
/
90
0
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>=
w
>
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/
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er::
70
0 paw 34
•v paw
paw
60
o
10
154
\
226
20
30
40
50
60
/0
80
DATE OF HEADING
Figure 15. Changes In relative grain yield with dltTerent dates or heading (Julian) in
three wheat genotypes.
29
1 10 ,----,---,----r--,---,--------r--....-------,-------,
100
90
~~
C'J
2
C)
w
>
r-
80
<I:
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W
cr::
70
PBW 34
PBW 154
\J
PBW 226
•
60
50
0
l..--..L.-_--'-_----l._ _. . L . - _ - - l - _ - - - - l ._ _. l - - _ - - l - _ - - - I
o
10
20
30
40
50
60
70
80
DATE OF HEADING
figure 16. Changes in relative GM2 with dlfl'erent dates or headllll (Julian) In three
wheat genotypes.
30
Appendix 1. Correlation coefficients for three genotypes between yield and grains per meter
square vs four different PTQ values during 7 years at Punjab Agricultural University in
Ludhiana, India.
PBW34
Yield
GM2
Year
PBW 154
Yield
GM2
PBW 226
Yield
GM2
PTQl
PTQ2
PTQ3
PTQ4
.58
.60
.65
.63
.56
.61
.68
.65
.06
.48
.69
.53
.11
.50
.64
.54
1986-87
PTQl
PTQ2
PTQ3
PTQ4
.82
.81
.57
.74
.77
.79
.59
.72
.34
.85
.51
.79
.30
.79
.45
.71
1987-88
PTQl
PTQ2
PTQ3
PTQ4
.62
.86
.48
.67
.84
.12
-.22
-.22
-.63
-.24
-.49
.09
.49
.43
.08
.38
-.40
.12
-.10
.25
.30
.71
.59
.87
1988-89
PTQI
PTQ2
PTQ3
PTQ4
.58
.88
.72
.88
.41
.74
.63
.71
.68
.96
.86
.91
.82
.92
.96
.80
.33
.70
.52
.75
.82
.93
.79
.89
1989-90
PTQI
PTQ2
PTQ3
PTQ4
-.96
-.81
-.94
-.89
-.86
-.80
-.52
-.45
-.42
-.19
.19
.20
.04
.48
.05
-.25
-.13
-.24
.76
.59
.61
.53
.44
.88
.68
.96
.46
.83
.67
.93
.12
.68
.38
.90
.22
.74
.49
.86
.00
.69
.33
.87
.59
.57
.41
.67
.40
.63
.40
.69
.67
.73
.57
.63
1985-86
1990-91
1991-92
PTQI:
PTQ2:
PTQ3:
PTQ4:
-~82
-.87
PTQI
PTQ2
PTQ3
PTQ4
PTQl
PTQ2
PTQ3
PTQ4
.13
.85
.31
.95
.35
.81
.55
.74
-30 H
From -20 H to + 10 H
-20 H
From -20 H to +20 H
31
CIMMYT Wheat Special Reports Completed or In Press
(As of Nov. 10, 1993)
Wheat Special Report No.1. Burnett, P.A., J. Robinson, B. Skovmand, A. MujeebKazi, and G.P. Hettel. 1991. Russian Wheat Aphid Research at CIMMYT: Current Status
and Future Goals. 27 pages.
Wheat Special Report No.2. He Zhonghu and Chen Tianyou. 1991. Wheat and Wheat
Breeding in China. 14 pages.
Wheat Special Report No.3. Meisner, CA. 1992. Impact of Crop Management
Research in Bangladesh: Implications of CIMMYT's Involvement Since 1983. 15 pages.
Wheat Special Report No.4. Skovmand, B. 1994. Wheat Cultivar Abbreviations. Paper
and diskette versions. In press.
Wheat Special Report No.5. Rajaram, S., and M. van Ginkel. 1993 (rev.). A Guide to
the CIMMYT Bread Wheat Section. 52 pages.
Wheat Special Report No.6. Meisner, CA., E. Acevedo, D. Flores, K. Sayre, I. OrtizMonasterio, and D. Byerlee. 1992. Wheat Production and Grower Practices in the Yaqui
Valley, Sonora, Mexico. 75 pages.
Wheat Special Report No. 7a. Fuentes-Davila, G. and G.P. Hettel, eds. 1992. Update on
Kamal Bunt Research in Mexico. 38 pages.
Reporte Especial de Trigo No. 7b. Fuentes-Davila, G., y G.P. Hettel, eds. 1992. Estado
actual de la investigacion sobre el carbon parcial en Mexico. 41 pages.
Wheat Special Report No.8. Fox, P.N., and G.P. Hettel, eds. 1992. Management and
Use of International Trial Data for Improving Breeding Efficiency. 100 pages.
Wheat Special Report No.9. Rajaram, S., E.E. Saari, and G.P. Hettel, eds. 1992. Durum
Wheats: Challenges and Opportunities. 190 pages.
Wheat Special Report No. 10. Rees, D., K. Sayre, E. Acevedo, T. Nava Sanchez, Z. Lu,
E. Zeiger, and A. Limon. 1993. Canopy Temperatures of Wheat: Relationship with Yield
and Potential as a Technique for Early Generation Selection. 32 pages.
Wheat Special Report No. 11. Mann, C.E., and B. Rerkasem, eds. 1992. Boron
deficiency in Wheat. 132 pages.
Wheat Special Report No. 12. Acevedo, E. 1992. Developing the Yield Potential of
Irrigated Bread Wheat: Basis for Physiological Research at CIMMYT. 18 pages.
Wheat Special Report No. 13. Morgunov, A.I. 1992. Wheat Breeding in the Former
USSR. 34 pages.
Wheat Special Report No. 14. Reynolds, M., E. Acevedo, O.A.A. Ageeb, S. Ahmed,
L.J.CB. Carvalho, M. Balata, R.A. Fischer, E. Ghanem, R.R. Hanchinal, C.E. Mann, L.
Okuyama, L.B. Olegbemi, G. Ortiz-Ferrara, M.A. Razzaque, and J.P. Tandon. 1992.
Results of the 1st International Heat Stress Genotype Experiment. 19 pages.
32
Wheat Special Report No. 15. Bertschinger, L. 1993. Research on BYD Viruses: A
Brief State of the Art of CIMMYT's Program on BYD and Its Future Research
Guidelines. In press.
Wheat Special Report No. 16. Acevedo, E., and G.P. Hettel, eds. A Guide to the
CIMMYT Wheat Crop Management & Physiology Subprogram. 161 pages.
Wheat Special Report No. 17. Huerta, J., and A.P. Roelfs. 1993. The Virulence
Analysis of Wheat Leaf and Stem Rust on a Worldwide Basis. In press.
Wheat Special Report No. 18. Bell, M.A., and R.A. Fischer. 1993. Guide to Soil
Measurements for Agronomic and Physiological Research in Small Grain Cereals. 40
pages.
Wheat Special Report No. 19. Woolston, J.E. 1993. Wheat, Barley, and Triticale
Cultivars: A List of Publications in Which National Cereal Breeders Have Noted the
Cooperation or Germplasm They Received from CIMMYT. 68 pages
Wheat Special Report No. 20. Balota, M., I. Amani, M.P. Reynolds, and E. Acevedo.
1993. An Evaluation of Membrane Thermostability and Canopy Temperature Depression
as Screening Traits for Heat Tolerance in Wheat. 26 pages.
Reporte Especial de Trigo No. 21a. Moreno, J.I., y L. Gilchrist S. 1993. La rona 0 tiz6n
la espicga del trigo. In press.
Wheat Special Report No. 21b. Moreno, J.I., and L. Gilchrist S. 1993. Fusarium head
blight of wheat. In press.
Wheat Special Report No. 22. Stefany, P. 1993. Vernalization Requirement and
Response to Day Length in Guiding Development in Wheat. 39 pages.
Wheat Special Report No. 23a (short version). Dhillon, S.S., and I. Ortiz-Monasterio
R. 1993. Effects of Date of Sowing on the Yield and Yield Components of Spring Wheat
and Their Relationships with Solar Radiation and Temperature at Ludhiana (Punjab),
India. 33 pages.
Wheat Special Report No. 23b (long version). Dhillon, S.S., and I. Ortiz-Monasterio R.
1993. Effects of Date of Sowing on the Yield and Yield Components of Spring Wheat
and Their Relationships with Solar Radiation and Temperature at Ludhiana (Punjab),
India. 83 pages.
Wheat Special Report No. 24. Saari, E.E., and G.P. Hettel, eds. 1993. Guide to the
CIMMYT Wheat Crop Protection Subprogram. In press.
Wheat Special Report No. 25. Reynolds, M.P., E. Acevedo, K.D. Sayre, and R.A.
Fischer. 1993. Adaptation of Wheat to the Canopy Environment: Physiological Evidence
that Selection for Vigor or Random Selection May Reduce the Frequency of High
Yielding Genotypes. 17 pages.
Wheat Special Report No. 26. Reynolds, M.P., K.D. Sayre, and H.E. Vivar. 1993.
Intercropping Cereals with N-Fixing Legume Species: A Method for Conserving Soil
Resources in Low-Input Systems. 14 pages.
33

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