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Duration of the vegetative and reproductive period in relation to yield performance of spring wheat
Eur. J. Agron., 1992, 1(3), 133-137
Duration of the vegetative and reproductive period in relation to yield performance of spring wheat R. C. Sharma Institute of Agriculture and Animal Science, Rampur, P.O. Box 5186, Kathmandu, Nepal.
Received 7 July 1991 ; accepted 14 October 1992. Abstract
The durations of the vegetative growth period (VGP) and the grain filling period (GFP) of cereal crops influence their yield. Thus, the optimization of VGP and GFP results in higher grain yield. This study was conducted to i) examine variation in growth periods of spring wheat (Triticum aestivum L.) genotypes ; ii) determine the proportions of entire growth period occupied by VGP and GFP ; and iii) examine associations between growth period durations and yield. Twelve wheat genotypes of diverse backgrounds were evaluated in replicated trials in Nepal over three years (1988 to 1990). The characters evaluated were VGP, GFP, crop duration period (CDP), the proportions of CDP occupied by VGP (PVGP) and GFP (PGFP), grain yield (GRY), and biomass yield (BMY). Year and genotype x year interactions were significant for all traits. Mean values for VGP, GFP, CDP, PGFP, GRY, and BMY were lower in 1988 and 1990 than in 1989. Significant positive correlations of GFP and PGFP with GRY and BMY suggested that selection for long GFP will lead to improved yields. The negative correlation between VGP and GFP suggested that selection for long GFP would also result in early heading. Results suggest that a combination of short VGP and long GFP may produce higher grain yield in wheat. Key-words : vegetative growth period, grain filling period, grain yield, biomass yield, genotype x environment interaction.
INTRODUCTION The life cycle of wheat (Triticum aestivum L.) can be divided into the vegetative growth period (VGP) and the grain filling period (GFP). The growth and vigour of wheat plants are determined by the assimilate accumulation during the VGP, while assimilates synthesized and partitioned during the GFP determine kernel growth and grain yield. High grain yields of wheat depend on an appropriate balance between assimilate accumulation during the VGP and photosynthate partitioning to the grain during the GFP. A longer GFP may permit a greater assimilate accumulation and a greater grain yield. Interrelationships between VGP and GFP and grain yield in cereals have been studied by several researchers, although findings are conflicting. Under optimum conditions, the contribution of preanthesis photosynthate reserves to final grain weight was found to be 5 to 10 per cent in wheat and 20 per cent in barley (Hordeum vulgare L.) (Evans and Wardlaw, 1976). Bingham (1969) found that a long VGP contributed to higher grain yield of wheat. A long VGP often resulted in high grain yield of barley (Askel and Johnson, 1961). Spiertz et al. (1971) and Daynard and Kannenberg (1976) found positive corISSN II61-0301192!03!133 05 $ 2.501 © Gauthier-Villars - ESAg
relations between the length of the GFP and grain yield in spring wheat and corn (Zea mays L.) hybrids, but some exceptions were found in the case of corn. Hanway and Russell (1969) also reported a positive relationship between the length of GFP and grain yield in corn. On the other hand, N ass and Reiser (1975) concluded that the length of the GFP was not important in determining grain yield in a study of 10 wheat cultivars. Gebeyehou et al. (1982) reported that VGP was positively though not significantly correlated with grain yield (r = 0.25), while GFP was significantly and positively correlated with yield (r = 0.39). There is also controversy on the optimum combination of VGP and GFP for grain yield. Bingham (1969) reported that both VGP and GFP were important for obtaining high grain yields of wheat but Knott and Gebeyehou (1987) found that there was no indication of an optimum combination of the lengths of the VGP and the GFP for maximum yield of wheat. In part, the reasons for these contradictory findings may lie in the role of environment on the durations of the VGP and the GFP. The optimum durations of the VGP and the GFP depend upon the environment, particularly temperature (Krenzer and Moss, 1975). The complex effects of environmental
R. C. Sharma
134
conditions on the VGP and the GFP in determining grain yield are evident from a report by Eastin (1972) who found that in sorghum (Sorghum bicolor (L.) Moench) a short VGP and a long GFP resulted in high grain yield in Nebraska, while the opposite was true under Texas conditions. The durations of the VGP and the GFP of barley differed under field conditions compared to growth chamber conditions, with higher values for the latter (Rasmussen et al., 1979). These authors explained the complex nature of the relationships among VGP, GFP, and maturity period in developing an optimum combination of these periods, and suggested the need for further studies on the influence of growth periods on grain yield. Because the literature indicates differences among research findings on the role of the VGP and GFP on grain yield and the optimum durations are likely to be very dependent on the environment, this study in Nepal was conducted with three objectives : (i) to examine the range of variation for the VGP and the GFP in a diverse set of wheat genotypes ; (ii) to analyze the proportion of the total life cycle of wheat in terms of vegetative and grain filling periods ; and (iii) to examine relationships of VGP and the GFP with GRY and BMY of wheat. MATERIALS AND METHODS
A set of 12 wheat genotypes representing a range of variation in plant type, grain yield potential, and genetic background was chosen for this study (Table 1). Included in the set were 10 commercial cultivars (Lerma 52, RR 21, NL 30, UP 262, Lumbini Triveni, Vinayak, Sildhartha, Vaskar, and Nepal251) and two advanced breeding lines (BL 1022 and
BL 1049). All the genotypes have been released or developed by the National Wheat Development Program of Nepal. All genotypes were evaluated in field trials at Rampur (altitude 228m above mean sea level), in three wheat growing seasons (1988-90). The experimental design was a randomized complete block with three replicates. Each plot, of 1.5 x 5 m, was seeded with six rows at 0.25 m row spacing. A seeding rate of 120 kg ha- 1 was used. The plots were seeded on 21, 23 and 20 November in 1987, 1988, and 1989, respectively. The optimum time for seeding wheat for this region is between 15 and 25 November. Fertilizers were applied at the rate of 100, 60 and 40 kg ha- 1 of N, P, and K, respectively, prior to seeding. Other cultural practices were as recommended for the area. The plots were harvested at maturity. In 1988, the wheat growing conditions were optimum with good residual soil moisture until the join ting stage, followed by drought : there was no rainfall from heading to maturity. The high temperatures and hot winds during the grain filling period reduced grain yield. In 1989, the environmental conditions were optimum throughout the growing season, with several rains. The cooler temperatures during grain filling period allowed a relatively longer grain development period. In 1990, the wheat growing conditions were normal until heading, followed by high temperatures and hot gusty winds during the grain filling period. The grain yields were below average. The weather data for the three growing seasons are given in Table 2. The length of the VGP was recorded as the number of days between seedling emergence and anthesis. Anthesis was recorded when approximately 50 per
Table 1. - Mean values of vegetative growth period (VGP), proportion of crop duration period (CDP) occupied by VGP (PVGP), CDP, grain filling period (GFP), grain yield (GRY), and biomass yield (BMY) for 12 wheat genotypes averaged over three years. Genotype
Lerma 52 RR 21 NL 30 UP 262 Lumbini Triveni Vinayak Siddhartha Vaskar BL 1049 Nepal 251 BL 1022
VGP days 79 a* 63 i 73 b 66 g 70 d 72 be 67 fg 67 fg 72c 68 e 65 h 66 g
PVGP %
64 54 60 56 59 60 56 56 60 58 54 56
a f b e c b e e b d f e
GFP days 45 55 49 53 49 48 54 53 48 49 56 52
h b e cd ef g be cd fg e a d
CDP days 124 118 123 119 119 120 121 120 120 117 121 118
a g ab d-f ef c-e cd c-e de g be fg
GRY kg ha- 1 2 3 3 3 3 2 3 2 3 3 3 3
130 462 131 768 101 994 355 946 350 338 577 239
e c cd a cd d a-d d a-d a-d ab b-d
BMY kg ha- 1 6 8 8 9 7 7 8 6 7 8 8 8
944 082 151 971 582 172 616 571 628 249 248 043
ef b-d b-d a c-e d-f b f b-e be be b-e
* Means followed by the same letter within a column are non-significantly different based on Duncan's New Multiple Range Test at p = 0.05. Eur. J. Agron.
135
Vegetative and reproductive period and yield in spring wheat
Table 2. -
Average monthly temperature and total monthly rainfall during wheat growing months in 3 years at Rampur, Nepal.
1987-88
1988-89
1989-90
1987-88
Rainfall (mm) 1988-89
25.4 21.8 17.5 16.2 19.1 22.8 27.3
24.8 21.0 16.3 14.5 16.7 21.5 26.3
26.4 19.9 15.8 16.2 17.7 23.0 26.3
170.7 0.0 12.0 0.0 4.7 39.4 101.2
60.2 0.0 1.0 49.5 1.0 33.5 0.0
Temperature* (OC)
Month October November December January February March April
* Average monthly temperature
= (maximum +
1989-90 43.0 0.3 2.0 0.0 28.6 41.4 28.5
minimum)/2.
cent of the spikes in a plot had exerted anthers. The length of GFP was determined as the number of days from anthesis to maturity. Maturity was recorded when glumes completely lost their green colour, following the procedure of Hanft and Wych (1982) and Knott and Gebeyehou (1987). The proportions of the CDP occupied by the VGP and the GFP (PVGP and PGFP, respectively) were calculated. At maturity, the plots were harvested by hand at ground level and individual plot bundles were air dried for one week. Biomass yield was recorded as the weight of the dry bundles which were then threshed, and grain yield determined. A combined analysis of variance of the three years' data was conducted using the MST AT ( 1986) microcomputer program. The correlation coefficients among various characters were computed separately for each year. The average correlations over years were calculated using Fisher's z-transformation as outlined by Steel and Torrie ( 1980).
RESULTS AND DISCUSSION A combined analysis of variance over years of VGP, GFP, CDP, GRY, BMY, PVGP and PGFP revealed significant effects of year on all traits (Table 3). Significant differences among genotypes
were found for each trait in each year. Genotype x year interactions were significant for all traits indicating that the relative responses of the 12 genotypes changed with years for these traits. However, the magnitude of the genotype x year interaction was much lower than the main effect of genotypes for all seven characters. Because of small size of the genotype x year interactions, only the genotypic means over years for the different characters are shown in Table 1. The VGP ranged from 62 to 75, 64 to 88, and 62 to 74 days respectively in 1988, 1989 and 1990 growing seasons (data not shown). RR 21 had the shortest VGP in all three years while Lerma 52 had the longest. All genotypes except Siddhartha and UP 262 had a longer VGP in 1989 than in the other two years. The average VGP of the 12 genotypes (Table 4) was longer in 1989 (73 days) than in 1988 and 1990 (68 and 67 days, respectively). The average PVGP of the 12 genotypes ranged between 55 and 64, 49 and 63, and 57 and 64 per cent in 1988, 1989 and 1990, respectively (data not shown). Several genotypes showed consistency in PVGP values over the three years. These included Lerma 52, NL 30, Triveni, and BL 1049. The remaining eight genotypes showed much variation in PVGP over the three years. The PVGP of the 12 wheat genotypes (Table 4) was less in 1989 (54 per cent) than in 1988 and 1990 (59 and 60 per cent, respectively).
Table 3. - Analysis of variance for vegetative growth period (VGP), grain filling period (GFP), crop duration period (CDP), grain yield (GRY), biomass yield (BMY), and proportion of CDP spent in VGP (PVGP), and in GFP (PGFP) of 12 wheat genotypes grown in 3 years. Source
df
VGP
GFP
Year (Yr) Replication/Y r Genotype (Geno) Geno x Yr Error
2 6 II 22 66
336.8 0.9 181.2 18.7 0.8
2708.5 7.6 106.9 23.7
Vol. 1, n° 3 - 1992
1.7
GRY COP (Mean squares) 4963.5 5.4 33.7 8.7 2.0
2323 182 !53 37 17
BMY
PVGP
PGFP
11 611 847 698 149 85
313.0 2.2 84.6 10.4 0.5
311.0 2.1 84.2 10.3 0.6
R. C. Sharma
136
Table 4. - Mean values of vegetative growth period (VGP), proportion of crop duration period (CDP) occupied by VGP (PVGP), CDP, grain filling period (GFP), grain yield (GRY), and biomass yield (BMY) in the three years averaged over the 12 wheat genatypes. Year
VGP days
1988 1989 1990
68 b+ 73 a 67 b
PVGP %
GFP days
CDP days
GRY kg ha- 1
BMY kg ha- 1
59 a 54 b 60 a
47 a 61 a 45 b
115 b 134 a 112 b
2 740 b 4 127 a 2 732 b
6 956 b 10 011 a 6 848 c
+ Means followed by the same letter within a column are non-significantly different based on Duncan's New Multiple Range Test at P = 0.05.
Grain filling periods varied from 43 to 53, 51 to 69, and 41 to 47 days in 1988, 1989 and 1990, respectively (data not shown). Lerma 52 consistently had a short GFP while Nepal 251 showed a long GFP in each year. The average GFP of the 12 (Table 4) genotypes was much longer in 1989 (61 days) than 1988 and 1990 (47 and 45 days, respectively). The range of CDP was 111-118, 128-139, and 108114 days in 1988, 1989 and 1990, respectively (data not shown). Lerma 52 took the longest time to mature in each of the three years. The genotypes with the shortest CDP varied with years. All genotypes had a longer CDP in 1989 compared to the other two years. The average CDP (Table 4) was longer in 1989 (134 days) than in 1988 and 1990 (115 and 112 days, respectively). The grain yield of the genotypes ranged from 1807 to 3230, 2767 to 4800, and 1817 to 3385 kg ha- 1 in 1988, 1989 and 1990, respectively (data not shown). UP 262 consistently had the greatest grain yield in all three years. The average grain yields in 1988 and 1990 were similar and lower than in 1989 (Table 4).
Table 5. 3 years.
VGP GFP CDP GRY BMY PVGP
Biomass yield varied from 5748 to 8289, 8211 to 12833, and 5650 to 8792 kg ha- 1 in 1988, 1989 and 1990, respectively (data not shown). The mean BMY of the genotypes was less in 1988 and 1990 than in 1989. UP 262 had the highest BMY in each year while Siddharta consistently yielded the least biomass. The mean values and the ranges for VGP, GFP, CDP, GRY, BMY, PVGP, and PGFP indicated a range of variation for these traits in the genotypes. The degree of variation changed in different years for all traits. The longer GFP in 1989 resulted in a higher GRY and BMY than in the other two years. The simple correlation coefficient r between VGP and GFP was - 0.874 (Table 5) which suggested that improvement in the GFP would be possible only by shortening the VGP. This finding was in agreement with that of Knott and Gebeyehou (1987) who found that VGP and GFP were negatively correlated. In the present study the length of the CDP appeared to be influenced more by VGP (r = 0.538) than by GFP (r = - 0.157). Grain yield showed a significant positive correlation with GFP (r = 0.597). This finding is in agreement with several previous reports (Spiertz et
Simple correlation coefficients among growth periods and other agronomic traits of 12 wheat genotypes grown in
GFP
CDP
GRY
BMY
PVGP
PGFP
- 0.874**
0.538** - 0.107
- 0.806** 0.597** - 0.419*
- 0.442* 0.428* - 0.145 0.790**
0.964** - 0.971** 0.339 - 0.656** - 0.450*
- 0.963** 0.971** - 0.348 0.654** 0.448* - 0.999**
*, ** Significantly different from zero at 0.05 and 0.01 probability levels, respectively. VGP = vegetative growth period, GFP = grain filling period, GRY = grain yield, BMY = biomass yield, CDP PVGP = proportion of CDP spent as VGP, PGFP = proportion of CDP spent as GFP.
= crop
duration period,
Eur. J. Agron.
Vegetative and reproductive period and yield in spring wheat
al., 1971 ; Daynard and Kannenberg, 1976; Hanway and Russell, 1969; and Gebeyehou et al., 1982). The VGP was negatively correlated (r = - 0.806) with GRY. This finding differs from that of Gebeyehou et al. (1982) and Bingham (1969). Grain yield was also significantly and negatively correlated with the CDP (r =- 0.419). Biomass yield was positively correlated with GFP and GRY but not with the VGP. Grain yield and BMY were positively correlated with PGFP but negatively correlated with PVGP. The results of this study indicate that wheat genotypes exhibited variation for growth periods that was influenced by environment and genotype x environment interactions. Selection for longer GFP may increase GRY and BMY. The presence of a strong negative correlation between VGP and GFP indicated that selection for shorter VGP may result in longer GFP. The negative correlation between VGP and GRY indicated that it may not be necessary to optimize VGP to obtain high GRY. Manipulation of GFP alone may result in changes in GRY.
REFERENCES Askel R. and Johnson L. V. P. (1961). Genetic studies in sowing-to-heading and heading-to-ripening periods in barley and their relation to yield and yield components. Can. J. Cytol., 3, 242-259. Bingham J. (1969). The physiological determinants of grain yield in cereals. Agric. Prog., 44, 30-42. Daynard T. B. and Kannenberg L. W. (1976). Relationships between length of the actual and effective grain filling periods and grain yield of com. Can. J. Plant. Sci., 56, 237-242. Eastin R. A. (1972). Photosynthesis and translocation in relation to plant development. In : Rao N. G. P. and House L. R. (Eds). Sorghum in the seventies. New Delhi : IBX and Oxford Co., 214-246.
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D
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3 - 1992
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Evans L. T. and Wardlaw I. F. (1976). Aspects of the comparative physiology of the grain yield in cereals. Adv. Agron., 28, 301-359. Gebeyehou G., Knott D. R. and Baker R. J. (1982). Relationships among duration of vegetative and grain filling phases, yield components and grain yield in durum wheat cultivars. Crop Sci., 22, 287-290. Hanft J. M. and Wych R. D. (1982). Visual indicators of physiological maturity of hard red spring wheat. Crop Sci., 22, 584-588. Hanway J. J. and Russell W. A. (1969). Dry matter accumulation in com (Zea mays L.) plants. Agron. J., 61, 947-951. Knott D. R. and Gebeyehou G. (1987). Relationship between the lengths of the vegetative and grain filling periods and agronomic characters in three durum wheat crosses. Crop Sci., 27, 875-880. Krenzer E. G. and Moss D. N. (1975). Carbon dioxide enrichment effects upon yield and yield components in wheat. Crop Sci., 15, 71-74. MSTAT (1986). A microcomputer program for the design, management, and analysis of agronomic research experiments. East Lansing, Michigan : Michigan State Univ. Nass H. G. and Reiser B. (1975). Grain filling period and grain relationships in spring wheat. Can. J. Plant. Sci., 55, 673-678. Rasmussen D. C., McLean I. and Tew T. L. (1979). Vegetative and grain filling periods of growth in barley. Crop Sci., 19, 5-9. Spiertz J. H. J., Tent B. A. and Kupers L. J.P. (1971). Relation between green area duration and grain yield in some varieties of wheat. Neth. J. agric. Sci., 19, 211-222. Steel R. G. D. and Torrie J. H. (1980). Principles and procedures of statistics. New York: McGraw-Hill Book Company.
Duration of the vegetative and reproductive period in relation to yield performance of spring wheat R. C. Sharma Institute of Agriculture and Animal Science, Rampur, P.O. Box 5186, Kathmandu, Nepal.
Received 7 July 1991 ; accepted 14 October 1992. Abstract
The durations of the vegetative growth period (VGP) and the grain filling period (GFP) of cereal crops influence their yield. Thus, the optimization of VGP and GFP results in higher grain yield. This study was conducted to i) examine variation in growth periods of spring wheat (Triticum aestivum L.) genotypes ; ii) determine the proportions of entire growth period occupied by VGP and GFP ; and iii) examine associations between growth period durations and yield. Twelve wheat genotypes of diverse backgrounds were evaluated in replicated trials in Nepal over three years (1988 to 1990). The characters evaluated were VGP, GFP, crop duration period (CDP), the proportions of CDP occupied by VGP (PVGP) and GFP (PGFP), grain yield (GRY), and biomass yield (BMY). Year and genotype x year interactions were significant for all traits. Mean values for VGP, GFP, CDP, PGFP, GRY, and BMY were lower in 1988 and 1990 than in 1989. Significant positive correlations of GFP and PGFP with GRY and BMY suggested that selection for long GFP will lead to improved yields. The negative correlation between VGP and GFP suggested that selection for long GFP would also result in early heading. Results suggest that a combination of short VGP and long GFP may produce higher grain yield in wheat. Key-words : vegetative growth period, grain filling period, grain yield, biomass yield, genotype x environment interaction.
INTRODUCTION The life cycle of wheat (Triticum aestivum L.) can be divided into the vegetative growth period (VGP) and the grain filling period (GFP). The growth and vigour of wheat plants are determined by the assimilate accumulation during the VGP, while assimilates synthesized and partitioned during the GFP determine kernel growth and grain yield. High grain yields of wheat depend on an appropriate balance between assimilate accumulation during the VGP and photosynthate partitioning to the grain during the GFP. A longer GFP may permit a greater assimilate accumulation and a greater grain yield. Interrelationships between VGP and GFP and grain yield in cereals have been studied by several researchers, although findings are conflicting. Under optimum conditions, the contribution of preanthesis photosynthate reserves to final grain weight was found to be 5 to 10 per cent in wheat and 20 per cent in barley (Hordeum vulgare L.) (Evans and Wardlaw, 1976). Bingham (1969) found that a long VGP contributed to higher grain yield of wheat. A long VGP often resulted in high grain yield of barley (Askel and Johnson, 1961). Spiertz et al. (1971) and Daynard and Kannenberg (1976) found positive corISSN II61-0301192!03!133 05 $ 2.501 © Gauthier-Villars - ESAg
relations between the length of the GFP and grain yield in spring wheat and corn (Zea mays L.) hybrids, but some exceptions were found in the case of corn. Hanway and Russell (1969) also reported a positive relationship between the length of GFP and grain yield in corn. On the other hand, N ass and Reiser (1975) concluded that the length of the GFP was not important in determining grain yield in a study of 10 wheat cultivars. Gebeyehou et al. (1982) reported that VGP was positively though not significantly correlated with grain yield (r = 0.25), while GFP was significantly and positively correlated with yield (r = 0.39). There is also controversy on the optimum combination of VGP and GFP for grain yield. Bingham (1969) reported that both VGP and GFP were important for obtaining high grain yields of wheat but Knott and Gebeyehou (1987) found that there was no indication of an optimum combination of the lengths of the VGP and the GFP for maximum yield of wheat. In part, the reasons for these contradictory findings may lie in the role of environment on the durations of the VGP and the GFP. The optimum durations of the VGP and the GFP depend upon the environment, particularly temperature (Krenzer and Moss, 1975). The complex effects of environmental
R. C. Sharma
134
conditions on the VGP and the GFP in determining grain yield are evident from a report by Eastin (1972) who found that in sorghum (Sorghum bicolor (L.) Moench) a short VGP and a long GFP resulted in high grain yield in Nebraska, while the opposite was true under Texas conditions. The durations of the VGP and the GFP of barley differed under field conditions compared to growth chamber conditions, with higher values for the latter (Rasmussen et al., 1979). These authors explained the complex nature of the relationships among VGP, GFP, and maturity period in developing an optimum combination of these periods, and suggested the need for further studies on the influence of growth periods on grain yield. Because the literature indicates differences among research findings on the role of the VGP and GFP on grain yield and the optimum durations are likely to be very dependent on the environment, this study in Nepal was conducted with three objectives : (i) to examine the range of variation for the VGP and the GFP in a diverse set of wheat genotypes ; (ii) to analyze the proportion of the total life cycle of wheat in terms of vegetative and grain filling periods ; and (iii) to examine relationships of VGP and the GFP with GRY and BMY of wheat. MATERIALS AND METHODS
A set of 12 wheat genotypes representing a range of variation in plant type, grain yield potential, and genetic background was chosen for this study (Table 1). Included in the set were 10 commercial cultivars (Lerma 52, RR 21, NL 30, UP 262, Lumbini Triveni, Vinayak, Sildhartha, Vaskar, and Nepal251) and two advanced breeding lines (BL 1022 and
BL 1049). All the genotypes have been released or developed by the National Wheat Development Program of Nepal. All genotypes were evaluated in field trials at Rampur (altitude 228m above mean sea level), in three wheat growing seasons (1988-90). The experimental design was a randomized complete block with three replicates. Each plot, of 1.5 x 5 m, was seeded with six rows at 0.25 m row spacing. A seeding rate of 120 kg ha- 1 was used. The plots were seeded on 21, 23 and 20 November in 1987, 1988, and 1989, respectively. The optimum time for seeding wheat for this region is between 15 and 25 November. Fertilizers were applied at the rate of 100, 60 and 40 kg ha- 1 of N, P, and K, respectively, prior to seeding. Other cultural practices were as recommended for the area. The plots were harvested at maturity. In 1988, the wheat growing conditions were optimum with good residual soil moisture until the join ting stage, followed by drought : there was no rainfall from heading to maturity. The high temperatures and hot winds during the grain filling period reduced grain yield. In 1989, the environmental conditions were optimum throughout the growing season, with several rains. The cooler temperatures during grain filling period allowed a relatively longer grain development period. In 1990, the wheat growing conditions were normal until heading, followed by high temperatures and hot gusty winds during the grain filling period. The grain yields were below average. The weather data for the three growing seasons are given in Table 2. The length of the VGP was recorded as the number of days between seedling emergence and anthesis. Anthesis was recorded when approximately 50 per
Table 1. - Mean values of vegetative growth period (VGP), proportion of crop duration period (CDP) occupied by VGP (PVGP), CDP, grain filling period (GFP), grain yield (GRY), and biomass yield (BMY) for 12 wheat genotypes averaged over three years. Genotype
Lerma 52 RR 21 NL 30 UP 262 Lumbini Triveni Vinayak Siddhartha Vaskar BL 1049 Nepal 251 BL 1022
VGP days 79 a* 63 i 73 b 66 g 70 d 72 be 67 fg 67 fg 72c 68 e 65 h 66 g
PVGP %
64 54 60 56 59 60 56 56 60 58 54 56
a f b e c b e e b d f e
GFP days 45 55 49 53 49 48 54 53 48 49 56 52
h b e cd ef g be cd fg e a d
CDP days 124 118 123 119 119 120 121 120 120 117 121 118
a g ab d-f ef c-e cd c-e de g be fg
GRY kg ha- 1 2 3 3 3 3 2 3 2 3 3 3 3
130 462 131 768 101 994 355 946 350 338 577 239
e c cd a cd d a-d d a-d a-d ab b-d
BMY kg ha- 1 6 8 8 9 7 7 8 6 7 8 8 8
944 082 151 971 582 172 616 571 628 249 248 043
ef b-d b-d a c-e d-f b f b-e be be b-e
* Means followed by the same letter within a column are non-significantly different based on Duncan's New Multiple Range Test at p = 0.05. Eur. J. Agron.
135
Vegetative and reproductive period and yield in spring wheat
Table 2. -
Average monthly temperature and total monthly rainfall during wheat growing months in 3 years at Rampur, Nepal.
1987-88
1988-89
1989-90
1987-88
Rainfall (mm) 1988-89
25.4 21.8 17.5 16.2 19.1 22.8 27.3
24.8 21.0 16.3 14.5 16.7 21.5 26.3
26.4 19.9 15.8 16.2 17.7 23.0 26.3
170.7 0.0 12.0 0.0 4.7 39.4 101.2
60.2 0.0 1.0 49.5 1.0 33.5 0.0
Temperature* (OC)
Month October November December January February March April
* Average monthly temperature
= (maximum +
1989-90 43.0 0.3 2.0 0.0 28.6 41.4 28.5
minimum)/2.
cent of the spikes in a plot had exerted anthers. The length of GFP was determined as the number of days from anthesis to maturity. Maturity was recorded when glumes completely lost their green colour, following the procedure of Hanft and Wych (1982) and Knott and Gebeyehou (1987). The proportions of the CDP occupied by the VGP and the GFP (PVGP and PGFP, respectively) were calculated. At maturity, the plots were harvested by hand at ground level and individual plot bundles were air dried for one week. Biomass yield was recorded as the weight of the dry bundles which were then threshed, and grain yield determined. A combined analysis of variance of the three years' data was conducted using the MST AT ( 1986) microcomputer program. The correlation coefficients among various characters were computed separately for each year. The average correlations over years were calculated using Fisher's z-transformation as outlined by Steel and Torrie ( 1980).
RESULTS AND DISCUSSION A combined analysis of variance over years of VGP, GFP, CDP, GRY, BMY, PVGP and PGFP revealed significant effects of year on all traits (Table 3). Significant differences among genotypes
were found for each trait in each year. Genotype x year interactions were significant for all traits indicating that the relative responses of the 12 genotypes changed with years for these traits. However, the magnitude of the genotype x year interaction was much lower than the main effect of genotypes for all seven characters. Because of small size of the genotype x year interactions, only the genotypic means over years for the different characters are shown in Table 1. The VGP ranged from 62 to 75, 64 to 88, and 62 to 74 days respectively in 1988, 1989 and 1990 growing seasons (data not shown). RR 21 had the shortest VGP in all three years while Lerma 52 had the longest. All genotypes except Siddhartha and UP 262 had a longer VGP in 1989 than in the other two years. The average VGP of the 12 genotypes (Table 4) was longer in 1989 (73 days) than in 1988 and 1990 (68 and 67 days, respectively). The average PVGP of the 12 genotypes ranged between 55 and 64, 49 and 63, and 57 and 64 per cent in 1988, 1989 and 1990, respectively (data not shown). Several genotypes showed consistency in PVGP values over the three years. These included Lerma 52, NL 30, Triveni, and BL 1049. The remaining eight genotypes showed much variation in PVGP over the three years. The PVGP of the 12 wheat genotypes (Table 4) was less in 1989 (54 per cent) than in 1988 and 1990 (59 and 60 per cent, respectively).
Table 3. - Analysis of variance for vegetative growth period (VGP), grain filling period (GFP), crop duration period (CDP), grain yield (GRY), biomass yield (BMY), and proportion of CDP spent in VGP (PVGP), and in GFP (PGFP) of 12 wheat genotypes grown in 3 years. Source
df
VGP
GFP
Year (Yr) Replication/Y r Genotype (Geno) Geno x Yr Error
2 6 II 22 66
336.8 0.9 181.2 18.7 0.8
2708.5 7.6 106.9 23.7
Vol. 1, n° 3 - 1992
1.7
GRY COP (Mean squares) 4963.5 5.4 33.7 8.7 2.0
2323 182 !53 37 17
BMY
PVGP
PGFP
11 611 847 698 149 85
313.0 2.2 84.6 10.4 0.5
311.0 2.1 84.2 10.3 0.6
R. C. Sharma
136
Table 4. - Mean values of vegetative growth period (VGP), proportion of crop duration period (CDP) occupied by VGP (PVGP), CDP, grain filling period (GFP), grain yield (GRY), and biomass yield (BMY) in the three years averaged over the 12 wheat genatypes. Year
VGP days
1988 1989 1990
68 b+ 73 a 67 b
PVGP %
GFP days
CDP days
GRY kg ha- 1
BMY kg ha- 1
59 a 54 b 60 a
47 a 61 a 45 b
115 b 134 a 112 b
2 740 b 4 127 a 2 732 b
6 956 b 10 011 a 6 848 c
+ Means followed by the same letter within a column are non-significantly different based on Duncan's New Multiple Range Test at P = 0.05.
Grain filling periods varied from 43 to 53, 51 to 69, and 41 to 47 days in 1988, 1989 and 1990, respectively (data not shown). Lerma 52 consistently had a short GFP while Nepal 251 showed a long GFP in each year. The average GFP of the 12 (Table 4) genotypes was much longer in 1989 (61 days) than 1988 and 1990 (47 and 45 days, respectively). The range of CDP was 111-118, 128-139, and 108114 days in 1988, 1989 and 1990, respectively (data not shown). Lerma 52 took the longest time to mature in each of the three years. The genotypes with the shortest CDP varied with years. All genotypes had a longer CDP in 1989 compared to the other two years. The average CDP (Table 4) was longer in 1989 (134 days) than in 1988 and 1990 (115 and 112 days, respectively). The grain yield of the genotypes ranged from 1807 to 3230, 2767 to 4800, and 1817 to 3385 kg ha- 1 in 1988, 1989 and 1990, respectively (data not shown). UP 262 consistently had the greatest grain yield in all three years. The average grain yields in 1988 and 1990 were similar and lower than in 1989 (Table 4).
Table 5. 3 years.
VGP GFP CDP GRY BMY PVGP
Biomass yield varied from 5748 to 8289, 8211 to 12833, and 5650 to 8792 kg ha- 1 in 1988, 1989 and 1990, respectively (data not shown). The mean BMY of the genotypes was less in 1988 and 1990 than in 1989. UP 262 had the highest BMY in each year while Siddharta consistently yielded the least biomass. The mean values and the ranges for VGP, GFP, CDP, GRY, BMY, PVGP, and PGFP indicated a range of variation for these traits in the genotypes. The degree of variation changed in different years for all traits. The longer GFP in 1989 resulted in a higher GRY and BMY than in the other two years. The simple correlation coefficient r between VGP and GFP was - 0.874 (Table 5) which suggested that improvement in the GFP would be possible only by shortening the VGP. This finding was in agreement with that of Knott and Gebeyehou (1987) who found that VGP and GFP were negatively correlated. In the present study the length of the CDP appeared to be influenced more by VGP (r = 0.538) than by GFP (r = - 0.157). Grain yield showed a significant positive correlation with GFP (r = 0.597). This finding is in agreement with several previous reports (Spiertz et
Simple correlation coefficients among growth periods and other agronomic traits of 12 wheat genotypes grown in
GFP
CDP
GRY
BMY
PVGP
PGFP
- 0.874**
0.538** - 0.107
- 0.806** 0.597** - 0.419*
- 0.442* 0.428* - 0.145 0.790**
0.964** - 0.971** 0.339 - 0.656** - 0.450*
- 0.963** 0.971** - 0.348 0.654** 0.448* - 0.999**
*, ** Significantly different from zero at 0.05 and 0.01 probability levels, respectively. VGP = vegetative growth period, GFP = grain filling period, GRY = grain yield, BMY = biomass yield, CDP PVGP = proportion of CDP spent as VGP, PGFP = proportion of CDP spent as GFP.
= crop
duration period,
Eur. J. Agron.
Vegetative and reproductive period and yield in spring wheat
al., 1971 ; Daynard and Kannenberg, 1976; Hanway and Russell, 1969; and Gebeyehou et al., 1982). The VGP was negatively correlated (r = - 0.806) with GRY. This finding differs from that of Gebeyehou et al. (1982) and Bingham (1969). Grain yield was also significantly and negatively correlated with the CDP (r =- 0.419). Biomass yield was positively correlated with GFP and GRY but not with the VGP. Grain yield and BMY were positively correlated with PGFP but negatively correlated with PVGP. The results of this study indicate that wheat genotypes exhibited variation for growth periods that was influenced by environment and genotype x environment interactions. Selection for longer GFP may increase GRY and BMY. The presence of a strong negative correlation between VGP and GFP indicated that selection for shorter VGP may result in longer GFP. The negative correlation between VGP and GRY indicated that it may not be necessary to optimize VGP to obtain high GRY. Manipulation of GFP alone may result in changes in GRY.
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