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a Dep. of Botany and Plant Sci., Univ. of California, Riverside, CA 92521-0124
b Dep. of Soil Sci., Faculty of Agriculture, Tishreen Univ., Lattakia, Syria
c Gryndlscot Farms, RR 9, Dunnville, Ontario N1A 2W8 Canada
* Corresponding author (bahman.ehdaie{at}ucr.edu)
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Grain growth and development in wheat depend on C from three sources: (i) carbohydrate produced after anthesis and translocated directly to the grains, (ii) carbohydrate produced after anthesis but stored temporarily in the stem before being remobilized to the grains, and (iii) carbohydrate produced before anthesis stored mainly in the stem and remobilized to grains during grain filling (Gallager et al., 1975; Daniels et al., 1982; Kobata et al., 1992).
Wheat crops grown in dryland areas may depend more on stem reserves for grain filling than crops grown under well-watered conditions. Under terminal drought, there is a rapid decline of photosynthesis after anthesis that limits the contribution of current assimilates to the grain (Johnson et al., 1981). The wheat canopy respires rapidly during grain filling (Gent and Kiyomoto, 1985; McCullough and Hunt, 1989). Flag leaf photosynthesis alone cannot support both respiration and grain growth under terminal stresses (Rawson et al., 1983). Therefore, a substantial amount of the carbohydrates used during grain filling in wheat must come from reserves assimilated before anthesis (Gent, 1994).
The estimated contribution of stored assimilates to grain yield in wheat depends on the genotype, experimental conditions, and the method of measuring stored carbohydrates. Stored reserves and their contribution to grain can be estimated by measuring postanthesis changes in internode dry matter (Hunt, 1979; Pheloung and Siddique, 1991; Borrell et al., 1993; Shakiba et al., 1996; Cruz-Agado et al., 2000), or/and changes in internode water-soluble carbohydrate content during grain-filling period (Davidson and Chevalier, 1992; Kiniry, 1993; Blum et al., 1994; Shakiba et al., 1996), or estimated by difference in canopy dry weight at anthesis and at maturity excluding the grains (Takami et al., 1990; Flood et al., 1995; Ehdaie and Waines, 1996).
In temperate cereals, the importance of stem reserve–utilization for grain filling under terminal drought and heat is derived mainly from preanthesis stem-storage capacity (Bonnett and Incoll, 1992; Borrell et al., 1993). Storage increases with longer stems and greater specific weight (Blum et al., 1997). The Rht1 and Rht2 dwarfing genes of wheat were found to reduce reserve storage by 35 and 39%, respectively, as a consequence of a 21% reduction in stem length (Borrell et al., 1993). However, mobilization efficiency, defined as the percentage of maximum stem weight mobilized, was lower in tall than in dwarf genotypes under favorable conditions. The Rht1 allele in ‘Maringa’ wheat reduced the amount of stored reserves contributed by the peduncle and penultimate internode to grain by 56 and 40%, averaged over both well-watered and droughted treatments, as a result of 18 and 16% reduction in the internode length, respectively (Shakiba et al., 1996).
There are two component traits involved in the extent of contribution of stored reserves to grain yield in wheat (Ehdaie and Waines, 1996). The first component is the ability to store assimilates in the stem and the second component is the efficiency with which the stored reserves are mobilized and translocated to grain. The second component is a function of the genotype's sink strength, which is dependent on the number of grains per spike and grain weight.
Little is known about the extent of genotypic variation for stem storage capacity and of the efficiency with which stored reserves are mobilized and transported to grain in wheat. Knowledge of the relationship between stem reserves and utilization with plant morphological characteristics, grain growth, grain yield, and its components could be used to develop wheats more adapted to harsh environments.
In this study, we evaluated the hypothesis that internode length, weight, and specific weight of wheat genotypes affect accumulation and mobilization of stem reserves. Ten diverse bread wheats along with a spring durum wheat (T. turgidum L. var. durum) were examined for postanthesis changes in internode dry weight, water-soluble carbohydrate content, and grain growth under well-watered and droughted field conditions across 2 yr to estimate genotypic variation in accumulation and mobilization of internode reserves.
This paper estimates the magnitude of mobilized dry matter and the mobilization efficiency in different internodes of the main stem. The data also provide the basis for a physiological and genotypic study of variation in internode water-soluble carbohydrate content and concentration and the relationship between internode changes with grain growth and grain yield, which will be reported in further papers of this series.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Field experiments were planted on 19 Dec. 1997 and on 15 Jan. 1998 in a Ramona Type A sandy loam soil (fine-loamy, mixed, thermic Type Haploxeralfs) at the Moreno Farm of the University of California Agricultural Experiment Station, Moreno Valley, CA. The 11 genotypes were planted in a split-plot design with four replicates (blocks). The main plots consisted of two irrigation treatments, namely well-watered and droughted treatment. The split-plot consisted of the genotypes. Plants in well-watered treatment were irrigated with sprinklers to minimize water shortage until they reached physiological maturity. Irrigation was terminated for plants in droughted treatment when plants in 50% of plots reached late booting stage on 23 Mar. 1998 and on 15 Apr. 1999. In the 1997 season, plants in well-watered treatment received 496 mm of water (132 mm irrigation + 364 mm rain) and those in droughted treatment received 430 mm of water (66 mm irrigation + 364 mm rain). In the 1998 season, plants in well-watered treatment received 332 mm of water (278 mm irrigation + 54 mm rain) and those in droughted treatment received 270 mm of water (216 mm irrigation + 54 mm rain). After irrigation was terminated in the droughted treatment, 63 and 30 mm of rain fell during early grain-filling period in the 1997 season and in the 1998 season, respectively.
Each plot consisted of six rows, 5 m in length. Interrow spacing was 20 cm and interplant spacing was 3 cm. The land was fallowed the previous year and 112 kg ha–1 urea fertilizer was incorporated into the soil before planting.
In each plot, 30 to 40 main tillers from the two middle rows next to the guard rows were tagged as spikes emerged from the flag leaf sheaths. Three main tillers were harvested at random at anthesis and at 10-d intervals after anthesis until maturity. The main tillers were harvested from the soil surface. After each harvest, leaf blades were removed and main tillers were immediately dried in a forced-air drier at 80°C for 48 h. Then, each main tiller was divided into spike and stem; then leaf sheaths were removed from the stem. Each stem was divided into three segments, namely peduncle (first internode below the spike including the distal node), penultimate internode (the internode below the peduncle including the distal node), and the lower internodes. The length and weight of each segment was measured, and then its specific weight (linear density) was calculated as the ratio of its weight to its length. The relative importance of internode length and weight in determination of specific weight was examined by comparing their standard partial regression coefficients (Draper and Smith, 1981). Also, in 1998 season, six tagged main tillers were harvested from the plots in well-watered treatment at maturity to measure the number of internodes comprising the lower internodes in each genotype and also to measure maximum diameter of the penultimate internode.
The magnitude of mobilized dry matter in each internode segment was estimated as the difference between postanthesis maximum and minimum weight. Mobilization efficiency of dry matter in each internode segment was estimated by the proportion (%) of mobilized dry matter relative to postanthesis maximum weight of that segment. An approximate standard deviation for mobilization efficiency (a ratio) was determined by assuming the numerator and denominator are independent. In this case, the estimates will be conservative since the numerator (amount of mobilized dry matter) and the denominator (postanthesis maximum weight) are positively correlated.
Dates of heading, anthesis, and physiological maturity were, respectively, determined from the four middle rows in each plot as: when 50% of spikes partially emerged from the flag leaf sheaths, when 50% of the spikes had extruded anthers, and when 50% of the spikes lost their green color.
Analysis of variance (ANOVA) was performed for each character measured or calculated for each year (Steel et al., 1997). The mean of the three samples in each harvest was used in the statistical analysis. The combined ANOVA was also performed across years, treating irrigation, genotype, and date of harvest as fixed effects and year, replication, and their interactions with irrigation, genotype, and date of harvest as random effects. Tests of significance of fixed effects were accomplished by using appropriate mean squares (Steel et al., 1997). Associations between characters were examined by correlation analysis. Means were compared using the LSD test (Steel et al., 1997).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The significant genotype x year interactions observed were mainly due to differences in changes in magnitude of genotype means rather than in ranking of the genotypes in different years. Only a few genotypes showed changes in rank for peduncle and penultimate internode weight under different irrigation treatments. On the basis of these observations, means averaged across years and irrigation regimes will be reported.
In the first growing season, the amount of rainfall was close to the long-term average. However, of 364 mm of rainfall, 81% fell before boot stage when drought was imposed on plants in droughted treatment, 12% fell between boot stage and heading, and 17% fell between heading and early grain-filling period. Since the soil type at the experimental site was sandy loam, soil water deficit was developed a few days after each rain. Therefore, despite large differences in the amount of rainfall between the first and second growing seasons, the percentage of reduction in stem weight were similar in both seasons; 25 and 28%, respectively.
Since there was genotypic variation in phenological periods, the correlation between the number of days each genotype was under drought in droughted treatment until physiological maturity and stem weight in droughted treatment was determined for both growing seasons. The correlation coefficients in the first season (r = 0.14) and in the second season (r = 0.11) were not significant, indicating that stem weight was not confounded by the genotypic differences in phenology.
Main Effect
Internode Length
Drought significantly reduced internode length and thus reduced the length of the main stem (Table 1). Greater reduction in length was found for peduncle than for penultimate and the lower internodes. There was tremendous variation for internode length among the genotypes. Yecora Rojo had the shortest peduncle (20.1 cm), penultimate (11.8 cm), and lower internodes (15.3 m). In contrast, Chinese Spring had the longest peduncle (30.3 cm), penultimate (24.6 cm), and lower internodes (39.1 cm).
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The penultimate and the lower internodes, on average, attained their maximum length at anthesis, whereas the peduncle reached its maximum length 10 d postanthesis (Table 1).
Internode Weight
Drought significantly reduced internode weight, which consequently reduced the weight of main stem (Table 2). The largest reduction was observed for peduncle followed by penultimate and the lower internodes. Significant variation was found among the genotypes for peduncle, penultimate, and the lower internode weight. Peduncle weight ranged from 259 mg for Wincora to 460 for Westbred Turbo. Penultimate internode weight varied from 259 mg for Yecora Rojo to 580 mg for Ramona 50. The lower internodes, which consisted of 2 to 4 internodes, had much greater weight compared with each of the top internodes. Weight of the lower internodes ranged from 434 mg for Yecora Rojo to 1053 mg for Westbred Turbo. Among the bread wheats, Anza (winter), Anza (spring), and Wincora also had relatively low basal internode weights (Table 2).
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Internode Specific Weight
Since internode weight is a function of internode length, internode weight was divided by length to determine internode specific weight or linear density (Table 3). Drought, on average, reduced specific weight. The penultimate and the lower internodes showed the highest reduction followed by the peduncle. Significant variation for internode specific weight was observed among the genotypes. Peduncle specific weight in Westbred Turbo was maximum (15.4 mg cm–1) followed by Yecora Rojo (13.9 mg cm–1), Ramona 50 (13.4 mg cm–1), and Express (12.6 mg cm–1). In contrast, No. 14 (10.2 mg cm–1), Maringa (10.5 mg cm–1), Chinese Spring (10.6 mg cm–1), and No. 49 (10.7 mg cm–1) showed the minimum specific weight for peduncle (Table 3). Penultimate internode specific weight was the highest for Ramona 50 (24.7 mg cm–1), followed by Westbred Turbo (24.5 mg cm–1), Yecora Rojo (22.2 mg cm–1), and Express (20.6 mg cm–1). In contrast, No. 14 (15.8 mg cm–1), Anza (winter) (16.8 mg cm–1), Maringa (16.9 mg cm–1), and Chinese Spring and No. 49 (17.1 mg cm–1) had the lowest penultimate specific weight. Specific weight for the lower internodes ranged from 21.0 mg cm–1 for Chinese Spring to 33.2 mg cm–1 for Ramona 50 (Table 3).
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Genotype x Date of Harvest Interaction
Peduncle Weight
Different trends for postanthesis changes in peduncle weight were observed among the genotypes (Fig. 1
). Durum wheat Westbred Turbo was different from the bread wheats examined with regards to peduncle weight, but its trend was similar to those of Anza (spring), Yecora Rojo, and Maringa. These genotypes showed the greatest increase in peduncle weight during the first 10 d after anthesis and reached their maximum weight 20 d postanthesis. Anza (winter) reached maximum peduncle weight 10 d postanthesis. No significant change in peduncle weight was observed in No. 49 and Wincora between 10 and 20 d postanthesis (Fig. 1). Ramona 50 was the only genotype which had maximum peduncle weight 30 d postanthesis.
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Peduncle Specific Weight
Westbred Turbo and Yecora Rojo had similar trends for postanthesis changes in peduncle specific weight (Fig. 2
). Trends for Express, Anza (spring), and Westbred Turbo and for No. 14, Maringa, and Chinese Spring were also similar. The peduncle in most of the genotypes reached maximum specific weight 20 d postanthesis, except for Anza (winter) and No. 49 that reached it in 10 d and for Ramona 50 that reached it in 30 d postanthesis (Fig. 2). The extent and rate of increase in peduncle specific weight (accumulation of dry matter per unit length of peduncle) during the first 20 d after anthesis for Yecora Rojo, 7.44 mg cm–1 and 0.37 mg cm–1 d–1, respectively, were highest among the genotypes. The extent and rate of subsequent decrease (mobilization of dry matter) over the next 30 d for Yecora Rojo, 6.72 mg cm–1 and 0.22 mg cm–1 d–1, respectively, were also the highest. In contrast, Chinese Spring demonstrated the lowest amount and rate of increase in specific weight during the first 20 d after anthesis, 2.41 mg cm–1 and 0.12 mg cm–1 d–1, respectively, and the slowest subsequent decrease, 1.56 mg cm–1 and 0.05 mg cm–1 d–1, respectively (Fig. 2).
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Dry Matter Mobilization and Efficiency
Peduncle
Drought, on average, reduced postanthesis maximum and minimum weights in peduncle by 32 and by 37%, respectively (Table 4). However, the amount of reduction varied for different genotypes. The estimate of mobilized dry matter, calculated as the difference between postanthesis maximum and minimum weight in peduncle, varied more in well-watered than in droughted conditions among genotypes. Mobilization efficiency, estimated as the ratio of mobilized dry matter to maximum weight, showed similar trends (Table 4). Mobilized dry matter from the peduncle, on average, was greater in droughted than in well-watered conditions by 18%. However, genotypes responded differently to drought for the amount of dry matter mobilized from the peduncle (Table 4). Mobilization efficiency in peduncle, on average, was greater under drought (33%) than well-watered (20%) treatment. All genotypes had greater dry matter mobilization efficiency in drought except No. 14, Ramona 50, and Yecora Rojo which had similar efficiency in both moisture regimes (Table 4).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The peduncle was, on average, longer than the penultimate internode in all the genotypes examined. The lower internodes in the majority of the genotypes consisted of three separate internodes, whereas in Ramona 50 they consisted of two and in No. 49 and Chinese Spring they consisted of four individual internodes. The lower internodes were progressively shorter down the stem.
Drought, on average, reduced main stem length by 9%. Since internodes in wheat are extended sequentially up the stem (Borrell et al., 1993), the reduction in stem length was reflected more on peduncle length (15%) than on penultimate internode length (9%), and the lower internodes length (3%).
The partitioning of main stem length into peduncle, penultimate, and the lower internodes length was different among the genotypes. Partitioning of stem length into different internodes has a bearing on reserve accumulation before and after anthesis. In tall landraces such as No. 14, No. 49, and Chinese Spring, the peduncle made up 31 to 33% of stem length, whereas in modern dwarf and semidwarfs, it made up 37 to 47% of stem length. A reverse trend was observed for the lower internodes. Durum wheat Westbred Turbo and Ramona 50 were exceptional with regards to partitioning of stem length into different internode lengths. The penultimate internode in Westbred Turbo made up only 18% and the lower internodes in Ramona 50 made up 25% of the main stem length; both were the lowest percentages observed among the genotypes.
Drought, on average, reduced main stem weight by 23%. This reduction was reflected more on peduncle (28%) and penultimate (27%) than on the weight of the lower internodes (19%). These differences among internode weights in response to drought were due to the time drought was initiated and the time each segment attained its maximum weight. Among the internode traits, the greatest variation was observed for internode weight; none of the genotypes examined had similar weight for peduncle, penultimate, and the lower internodes. There was a positive correlation between stem weight and stem length (r = 0.76, P < 0.05), as also reported by Hunt (1979).
Maximum stem weight in all genotypes, except Ramona 50, was attained 20 d postanthesis. Rawson and Evans (1971), in a study of six wheat cultivars, reported that maximum stem weight was reached from 7 to 21 d after anthesis. They also reported that the period from full plant height to maximum stem weight varied from 2 to 15 d. Hunt (1979), in a study of 22 wheat cultivars, reported only one cultivar in which full stem length was reached before maximum stem weight. In the present study, only in No. 49, Anza (winter), and Wincora was full stem length attained before maximum stem weight.
The genotypic differences in mean stem weight and maximum stem weight were not related to the number of days from sowing to anthesis. For example, number of days from sowing to anthesis was 107 d for No. 14 and Express, but the stem weights for the two genotypes were 1464 and 1184 mg, respectively. In contrast, Chinese Spring and Ramona 50 reached anthesis 113 and 99 d after sowing, but they had similar stem weights, 1582.4 and 1560.2 mg, respectively. Hunt (1979) reported that maximum stem weight was not correlated to the timing of spike emergence. The lack of close association between stem weight or maximum weight and time of spike emergence and anthesis indicate that stem weight can be changed in wheat breeding programs without significantly affecting the phenological periods.
Significant genotypic differences were found for internode specific weight (linear density). As internodes lengths remained constant after reaching their maximum length, increase in specific weight represented deposition of dry matter and subsequent decrease represented mobilization and translocation of dry matter. Specific weight of stem segments was progressively greater down the stem in all genotypes examined, which concurs with the observations reported by Borrell et al. (1993).
Drought decreased stem specific weight by 16%. This reduction was mainly due to reduction in stem weight (32%) rather than in stem length (9%). The standard partial correlation coefficients calculated, using the overall mean of different stem internodes of the wheat cultivars, indicated that stem weight had a greater effect (1.22) on the determination of specific weight than stem length (–1.00). These observations indicate that selection for stem weight is more efficient to increase stem specific weight than selection for shorter stem.
Drought reduced maximum weight in the peduncle by 32%, in the penultimate internode by 26%, and in the lower internodes by 14%. These differences in percentage reduction in response to drought were due to time of initiation of drought and the time each segment attained its maximum weight. Mean mobilized dry matter, calculated as the difference between postanthesis maximum and minimum weight, was greater in droughted than in well-watered conditions for peduncle, but a reverse trend was found for penultimate and for the lower internodes. However, for each segment, different trends for mobilized dry matter were found among the genotypes under both water regimes. Only landrace No. 49 showed greater dry matter mobilized from all three segments of main stem in droughted than in well-watered conditions.
Terminal drought increased dry matter mobilization efficiency by 65% in peduncle, by 11% in penultimate internode, and by 5% in the lower internodes, as was also reported by Yang et al. (2001). The stem segments responded differently to drought because of their differences in growth stage and the time of initiation of terminal drought. Postanthesis maximum weight under drought compared with that in well-watered treatment was reduced by 32% in peduncle, by 26% in penultimate internode, and by 14% in the lower internodes, whereas postanthesis minimum weight was reduced by 37, 30, and 18%, respectively. As a result, the lower internodes and penultimate internode had similar mobilization efficiency (40 and 39%, respectively), but both were greater than that of peduncle (33%). However, significant genotypic variation for mobilization efficiency of dry matter were observed under both irrigation treatments, indicating that this trait can be manipulated in breeding programs. Only landrace No. 49 had greater mobilization efficiency in all segments of the main stem in droughted than in well-watered conditions.
Dry matter mobilized in droughted conditions was significantly correlated with peduncle, penultimate, and the lower internodes maximum weight (r = 0.74, r = 0.80, and r = 90, P < 0.01, respectively). Also, positive correlations were found between mobilized dry matter and maximum weight for peduncle and penultimate (r = 0.61 and r = 71, P < 0.05, respectively), and for the lower internodes (r = 0.58, P < 0.10) in well-watered conditions.
Stem length was not correlated with stem mobilized dry matter. For example, No. 49 and Wincora, on average, had similar stem mobilized dry matter, 565 and 557 mg, but differed in stem length, 87.4 and 56.0 cm, respectively. In contrast, Anza (spring) and Express had similar stem length, 61.6 and 59.7 cm, but differed in stem mobilized dry matter 460 and 662 mg, respectively. Rawson and Evans (1971) also reported that the amount of materials lost from the stems of wheat plants, whether measured as dry weight or as 14C, was uncorrelated to stem height. However, positive correlation between final plant height and mobilization of stem reserves in wheat was reported by Hunt (1979) and Borrell et al. (1993).
As expected, time to anthesis in Anza (winter) and Wincora was delayed by 6 and 11 d compared with their spring types, Anza (spring) and Yecora Rojo, respectively. The presence of the vernalization gene vrn1 in Anza (winter) and in Wincora, on average, reduced stem specific weight by 6%, mobilized dry matter by 20 and 10%, and mobilization efficiency by 12 and 19%, respectively. Thus, incorporation of vernalization gene vrn1 in spring wheat cultivars had negative effects on stem reserves accumulation and mobilization.
Developmentally, potential stem reserve accumulation and subsequent mobilization in wheat depends on stem length and stem specific weight. Our study demonstrated substantial genotypic variation for these traits in different internodes of the main stem. Dry matter accumulation and mobilization varied along the stem and in well-watered and droughted field conditions. More than 50% of the stem dry matter was, on average, stored in the lower internodes. In regions with Mediterranean climates, spring wheat is typically planted in late autumn or early winter and harvested in early summer. Thus, the crop is sown under conditions when rainfall and temperature are favorable for plant growth before anthesis, and then it matures into a terminal drought and heat. Under favorable conditions, carbon assimilation rates are higher (Davidson and Chevalier, 1992), and a large portion of assimilates is accumulated in the lower internodes which attain their maximum length before or during anthesis. Therefore, the lower internodes should have appropriate length to reach their potential for accumulation of dry matter before anthesis and a major source for dry matter mobilization after anthesis.
The lower internodes in Yecora Rojo, a dwarf cultivar possessing dwarfing genes Rht1 and Rht2, was the shortest (15.3 cm) and together they made up 32% of the main stem length. In comparison, the lower internodes in Express, a semidwarf cultivar possessing Rht1, was 22.9 cm and together they made up 38% of the main stem length. Stem weight in Yecora Rojo was the lowest among the genotypes examined and had less mobilized stem dry matter than Express. This was due to dwarf stature of Yecora Rojo and relatively short penultimate and lower internodes in this cultivar which limited the accumulation of a large amount of stem reserves especially before anthesis.
Plant height appears to be an important component of grain yield in bread wheat. Ehdaie and Waines (1994), using a set of near-isogenic lines (eight genotypes) for plant height in a spring bread wheat, found a parabolic relationship between plant height and transpiration efficiency, water-use efficiency, and grain yield. The optimum plant height to maximize these characters was between 80 and 100 cm. Gent (1995), using a set of near-isogenic lines (four genotypes) for plant height in a winter bread wheat, concluded that genotypes with plant height ranging between 80 and 90 cm had higher canopy light interception, gas exchange, biomass, and grain yield compared with either taller and shorter genotypes.
The popular modern bread wheat cultivars Yecora Rojo and Express and the old cultivar Ramona 50 demonstrated relatively greater rate and/or extent of dry matter accumulation and subsequent mobilization per unit stem length. Genotypes with greater rates of dry matter accumulation and mobilization are exposed less to the depressing effects of terminal stresses than those with lower rates. The peduncle and penultimate internode weights in Yecora Rojo, Ramona 50, and Express were depressed less by drought compared with the other genotypes. Dry matter mobilized from all three segments of main stem in landrace No. 49 increased in response to terminal drought.
On the basis of the results of this study, bread wheat breeding programs aiming to maximize stem reserve accumulation and mobilization in terminal stressful environments, should consider optimum plant height, with balanced partitioning of stem length into lower and upper internodes and greater stem specific weight as simultaneous selection criteria. Maximum specific weight was positively correlated with stem mobilized dry matter (r = 0.64, P < 0.05), averaged over years and irrigation treatments. Crosses between No. 49 and other genotypes such as Yecora Rojo or Express may produce offspring with improved dry matter accumulation and mobilization in stressful environments.
In the second paper of this series, postanthesis variation in internode water-soluble carbohydrate content and concentration will be reported.
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ACKNOWLEDGMENTS |
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Received for publication April 26, 2005.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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B. Ehdaie, G. A. Alloush, M. A. Madore, and J. G. Waines Genotypic Variation for Stem Reserves and Mobilization in Wheat: II. Postanthesis Changes in Internode Water-Soluble Carbohydrates Crop Sci., September 8, 2006; 46(5): 2093 - 2103. [Abstract] [Full Text] [PDF]
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