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a Dep. of Botany and Plant Sci., Univ. of California, Riverside, CA 92521-0124
b Dep. of Biology, Sonoma State Univ., Rohnert Park, CA 94928-3613
* Corresponding author (bahman.ehdaie{at}ucr.edu)
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: HI, harvest index • STI, stress tolerance index • WUE, water-use efficiency
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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The presence of 1RS.1BL in some hard red winter wheats was associated with higher grain yield, aerial biomass, grain weight, and spikelet fertility (Carver and Rayburn, 1994; Schlegel and Meinel, 1994; Moreno-Sevilla et al., 1995a). However, Moreno-Sevilla et al. (1995b), using a different hard red winter wheat background, reported no yield advantage associated with 1RS.1BL lines. McKendry et al. (1996) reported reduced plant height and delayed heading with the presence of 1RS.1BL, but found no significant yield advantage in soft red winter wheat. Using a set of genetically diverse spring wheat cultivars, Villareal et al. (1991)(1994) found a positive effect of 1RS.1BL on aerial biomass at maturity, spikes per square meter, grain weight, and test weight, but no significant effects on grain yield were detected.
In two sets of 1RS.1BL lines derived from crosses involving ‘Seri M82’, Villareal et al. (1995)(1998) reported higher grain yield, aerial biomass at maturity, grains per spike, grain weight, and test weight associated with 1RS.1BL under optimum and reduced moisture conditions. In these studies, the 1RS.1BL lines delayed flowering and maturity, but had no consistent effect on plant height, harvest index (HI), grains per square meter, and aerial biomass at maturity. Singh et al. (1998) found that the 1RS.1BL translocation in spring bread wheat had a negative effect on grain yield under optimum and droughted conditions.
Another wheat-rye translocation that is commonly used is 1RS.1AL. The 1RS.1AL translocations derived from three winter x spring wheat crosses exhibited increased grain yield, aerial biomass at maturity, spikes per square meter, and test weight under optimum and reduced irrigation conditions compared with their checks (Villareal et al., 1996). These lines showed greater grain weight, delayed maturity, and longer grain filling periods under optimum irrigation. In hard red winter wheat, the presence of 1RS.1AL had no significant effects on grain yield or grain weight (Graybosch et al., 1999). Espitia-Rangel et al. (1999) reported that the 1RS.1AL translocation in winter wheat ‘Nekota’ had a small effect on agronomic performance or environmental stability.
Research on the effect of 1RS.1DL on agronomic performance and end-use quality in bread wheat is limited. The presence of 1RS.1DL in ‘Gabo’ wheat genetic background caused a reduction in grain yield and had a detrimental effect on bread making quality (Koebner and Shepherd, 1988).
The disadvantage of using certain 1RS translocations is that they may reduce the end-use quality of wheat (Dhaliwal et al., 1987; Martin and Stewart, 1990). Graybosch et al. (1993) reported that the 1RS.1AL translocation was less detrimental to dough strength than the 1RS.1BL translocation.
There is evidence that rye has the most highly developed root system among the temperate cereals and it is more tolerant to abiotic stresses such as drought, heat, and cold than bread wheat (Starzycki, 1976). Evaluation of the disomic additions of ‘Imperial’ rye chromosomes to ‘Chinese Spring’ wheat indicated that chromosome 2R increased water-use efficiency and improved rooting characteristics of the recipient wheat cultivar (Lahsaiezadeh et al., 1983; Shah, 1992). The translocation line 2AS.2RL of bread wheat Chinese Spring and Imperial rye surpassed Chinese Spring for grain yield, shoot biomass at maturity, root biomass, and water-use efficiency, especially in droughted conditions (Lahsaiezadeh et al., 1983; Ehdaie et al., 1991, 1998). Furthermore, the long arm of chromosome 2R carries genes for resistance to tan spot [Pyrenophora tritici-repentis (Died.) Drechs.] and Hessian fly [Mayetiola destructor (Say)] (Hatchett et al., 1993; Lee et al., 1996). The 2BS.2RL translocation in bread wheat ‘Hamlet’ was evaluated for bread making quality (Knackstedt et al., 1994). The 2BS.2RL translocation, in contrast to 1RS translocations, did not have a detrimental effect on milling or baking quality of wheat. This translocation showed increased grain yield, aerial biomass at maturity, seeds per spike, and seeds per plant (Fritz and Sears, 1991). However, it delayed maturity and reduced grain weight and HI.
The yield advantage of wheat-rye translocations reported under reduced moisture conditions could be due to their greater water-use efficiency or rooting ability than their nontranslocation counterparts. As far as we are aware, water-use efficiency and rooting ability of wheat-rye translocations have not been studied in translocations involving 1RS, 2RS, and 2RL.
The major objectives of our study were to (i) determine the effect of translocations 1RS.1AL, 1RS.1BL, 1RS.1DL, 2RS.2BL, and 2BS.2RL on root biomass and water-use efficiency when grown in pots under well-watered and droughted conditions and (ii) evaluate field performance of these translocation lines under optimum and terminal drought conditions in the disease-free environment of southern California.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Centric translocations of chromosome 2R from spring rye cultivar Blanco to chromosome 2B of wheat were produced in the wheat cultivar Chinese Spring by centric breakage-fusion (Lukaszewski, 1993; Brunell et al., 1999) and transferred to Pavon wheat by the backcross procedure. After seven backcrosses, the translocation heterozygotes, which were developed from two separate backcross programs, were self-pollinated. Among their progeny, translocation homozygotes 2RS.2BL and 2BS.2RL and their respective 2B disomic sibs were isolated and grown. All cytological analyses used C-banding for chromosome identification.
The translocation lines involving chromosome 1 and 2 of Pavon (5 lines) along with the 2B disomic sibs, 2B1 and 2B2 (used as checks for 2RS.2BL and 2BS.2RL, respectively), the Kavkaz translocation line (1RS.1BLK), Pavon, and ‘Yecora Rojo’ were used in this study. Seeds of the lines were kindly donated by Dr. A.J. Lukaszewski, University of California, Riverside. Pavon is a spring bread wheat cultivar developed at CIMMYT and recommended for cultivation under irrigated conditions (Calhoun et al., 1994). It is very susceptible to drought, particularly during the grain filling period (Bruckner and Frohberg, 1987). Yecora Rojo is a dwarf, early maturing spring bread wheat cultivar derived from the CIMMYT breeding program and it is still a commercial bread wheat in southern California.
Pot Experiments
Two separate pot experiments were conducted in an unheated glasshouse at the University of California, Riverside, in 1997 and 1998. One experiment used Pavon and its 1RS translocation lines (1RS.1AL, 1RS.1BL, 1RS.1DL) and the original 1RS.1BLK. The other experiment used Pavon and its 2RS and 2RL translocation lines and their respective checks 2B1 and 2B2. For each experiment, we used a factorial design with 10 treatments (5 genotypes x 2 irrigation regimes), arranged in a randomized complete block design with four replicates.
Seeds from each genotype were soaked in water on 7 Jan. 1997 and on 6 Jan. 1998 for 24 h before being planted into wooden flats. Ten days later, one-leaf seedlings with similar growth were transplanted to plastic pots. Each plastic pot contained a plastic bag filled with 5.0 kg of soil composed of 800 g kg-1 sand, 162 g kg-1 silt, and 38 g kg-1 clay with water-holding capacity of 
260 g kg-1. Each replicate had a similarly treated but unplanted pot to quantify the evaporative water. Each pot was brought to water-holding capacity by adding a predetermined amount of half-strength Hoagland solution (Hoagland and Arnon, 1950) before transplanting a seedling into it. Pots were irrigated with the same solution throughout the study. One day after transplanting the seedlings, 80 g of small-sized perlite was added to the top of each pot to reduce surface evaporation. Pots were weighed every 2 or 3 d and an amount of solution equal to the loss in weight was added.
In the well-watered treatment, hereafter referred to as the wet treatment, pots were irrigated as described until the color of the main tiller of the plants turned yellow. In the droughted treatment, hereafter referred to as the dry treatment, drought was initiated at the early booting stage by adding 33% of solution needed to bring the pots to initial weight. Genotypes received different amounts of solution in both wet and dry treatments due to genotypic differences in days to booting stage and maturity. In the first experiment, booting stage ranged from 67 to 70 d and maturity ranged from 111 to 114 d. In the second experiment, booting stage ranged from 64 to 68 d and maturity ranged from 106 to 112 d. Mean evaporation water calculated from the unplanted pots was from 14.7 to 16.9% in 1997 and from 16.6 to 18.5% in 1998 of total water applied in the experiment. These values overestimate the actual amount of water evaporated from the planted pots.
Plants were harvested at maturity. Shoots were removed from roots at the soil surface. The pots were weighed to the nearest gram, and the soil was carefully washed from the roots. Plant parts were dried at 65°C for 10 d before weighing. The total amount of water used was calculated as the difference between final and initial pot weight plus the amount of water supplied to each pot (Ehdaie et al., 1991; Ehdaie and Waines, 1993). Thus, the total water used included both transpired and evaporative water. Phenological periods such as days from sowing to early booting, to heading, to anthesis, and to maturity were recorded. Number of tillers and spikes, plant height, root dry matter, shoot dry matter, and total dry matter per plant were measured. Plant water-use efficiency was calculated as grams total dry matter per kilogram water used (Ehdaie, 1995).
Field Experiments
Field experiments were planted on 13 Dec. 1999 and on 14 Dec. 2000 in a Ramona Type A sandy loam soil (fine-loamy, mixed, thermic Typic Haploxeralfs) at the Moreno Farm of the University of California Agricultural Experiment Station, Moreno Valley, CA. The nine wheat genotypes used in the glasshouse study, plus Yecora Rojo, were planted in a split-plot design with four replicates (blocks). The main plots consisted of two irrigation treatments, namely well-watered (wet) and droughted (dry) treatments. The split-plots consisted of the genotypes. Plants in the wet treatment were irrigated with sprinklers to minimize water shortage until they reached maturity. Irrigation was terminated for plants in the dry treatment when plants in 50% of plots reached heading stage. In 1999, plants in the wet treatment received 440 mm of water (250.5 mm irrigation + 189.5 mm rain) and those in the dry treatment received 322.5 mm of water (133.0 mm irrigation + 189.5 mm rain). In 2000, plants in the wet treatment received 404 mm of water (225.5 mm irrigation + 181.5 mm rain) and those in the dry treatment received 329.0 mm of water (147.5 mm irrigation + 181.5 mm rain). After irrigation was terminated in the dry treatment, 18.8 mm of rain fell during the grain-filling period in 1999 and 7.3 mm in 2000.
Each plot consisted of six rows, 5.0 m in length. Interrow spacing was 20 cm and interplant spacing was 3 cm. The land was fallowed the previous year and 112.0 kg ha-1 urea fertilizer were added to the soil before planting. The two middle rows in each plot were used to harvest 1-m length of plants at maturity to determine shoot biomass and grain yield. Plant height from soil surface to the tip of a spike (excluding awns) was measured from three randomly chosen spots in each plot at maturity. Two 50-cm lengths of two of the middle rows in each plot were used to count the number of tillers and spikes at maturity. Five spikes were randomly chosen from each plot to determine mean number of grains per spike and grain weight. Harvest index was calculated as the ratio of grain yield to shoot biomass. In 2000 only, one 1-m length of plants at anthesis was harvested from the second and fifth rows and immediately were dried in a forced-air drier at 60°C for 6 d to determine the relationship between shoot biomass at anthesis and grain weight and grain yield at maturity. Days from plant emergence to boot stage, to heading, to anthesis, and to maturity were recorded. Grain filling period was calculated as the difference between days to maturity and days to anthesis.
Analysis of variance was performed for each character measured in the glasshouse experiments and the field experiment for each year (Steel et al., 1997). The combined ANOVA was also performed across years for the glasshouse experiments and for the field experiments. Associations among characters were examined by correlation analysis. The key comparisons in our study were between Pavon and each of 1RS.1AL, 1RS.1BL, and 1RS.1DL translocations, between 2RS.2BL and its check 2B1, between 2BS.2RL and its check 2B2, and between 1RS.1BL and 1RS.1BLK. Mean comparisons between Pavon and its 1RS translocations used Dunnett's test (control vs. treatments) and other comparisons utilized the LSD test (Steel et al., 1997).
A stress tolerance index (STI) was used to characterize relative response of each genotype to stressed field conditions (Fernandez, 1992). The index was calculated from genotype means using the generalized formula
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P and S are mean yield in nonstress and stress environment, respectively. Therefore, STI is a function of relative performance of a genotype in nonstress 
, and stress 
environments and the stress intensity 
. Greater values of STI for a genotype indicate greater stress tolerance and yield potential. |
RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Mean values for Pavon and its 1RS translocation lines under wet and dry treatments are presented in Table 1. Experimental precision was good as indicated by the small to intermediate coefficients of variation for all the measured characters (Table 1). Pavon and its 1RS translocation lines were similar in plant maturity under both treatments (Table 1). The 1RS translocations showed a negative trend for plant height, but a positive trend for number of tillers and spikes per plant. A strong positive trend was shown by the 1RS translocations for root production (Table 1). Root dry matter increased significantly in 1RS.1AL and 1RS.1DL in well-watered and only in 1RS.1AL in droughted conditions. The relative increases in root dry matter in 1RS translocations were consistent in both treatments. Roots in the 1RS translocation lines were more branched and narrower than those in Pavon. Increase in root dry matter in the 1RS translocations did not have a depressing effect on shoot dry matter or grain yield (Table 1). In fact, the 1RS translocations showed a positive trend for total dry matter. The 1RS translocations also exhibited a positive trend for total water used. Since days to maturity were similar for Pavon and its 1RS translocations, it appears that the 1RS translocations had increased transpiration rates by using more water and producing more dry matter per day than Pavon. Total dry matter produced is positively and linearly correlated to total water used (Hubick et al., 1986; Ismail and Hall, 1992; Ehdaie, 1995). The presence of 1RS translocations in the background of Pavon had no significant effects on grain yield, number of grains per plant, grain weight, and water-use efficiency (WUE; Table 1).
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The presence of 2RS.2BL in the Pavon background, in general, delayed maturity and increased the number of tillers per plant (Table 2). Under well-watered conditions, number of spikes per plant increased, whereas grain weight decreased in the presence of 2RS.2BL. Grain yield, number of grains per plant, and grain weight exhibited negative trends in the presence of the 2RS.2BL translocation (Table 2). The short arm of chromosome 2 of rye, 2RS, is partially homeologous to the short arms of both group 2 and 6 chromosomes of wheat (Naranjo et al., 1987; Devos et al., 1993). Therefore, 2RS is not capable of fully compensating for the absence of 2BS (Brunell et al., 1999) and a reduction in plant performance is expected in 2RS.2BL translocations as reported by Gupta et al. (1989) and also confirmed by our observations.
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The results obtained from the pot experiments for the two reciprocal centric translocations 2RS.2BL and 2BS.2RL were unexpected. Since the long arm of chromosome 2 of rye, 2RL, is homeologous to 2BL (Brunell et al., 1999), the presence of 2BS.2RL translocation was expected to have more positive and less negative effects on plant performance than those of the 2RS.2BL translocation. However, such a trend was not observed (Table 2).
Field Experiments
The combined ANOVA (not shown) indicated highly significant main effects for year, irrigation, and genotype for most of the characters examined. The year x irrigation, genotype x year, genotype x irrigation, and genotype x year x irrigation interactions were significant or highly significant for most of the characters examined. The genotype x year interactions were mainly due to changes in the magnitude rather than ranking of the genotypic means in different years. Thus, means averaged across years are reported.
Experimental precision was high as indicated by the small coefficients of variation for all the measured characters, except for grain yield (Table 3). The presence of 1RS in the Pavon background delayed maturity by 3 d under wet and dry field conditions (Table 3), which was in agreement with other reports (Carver and Rayburn, 1994; Villareal et al., 1995, 1996, 1998; Singh et al., 1998). Compared with Pavon, grain filling period was longer in 1RS.1AL by 7 d and in 1RS.1BL by 5 d under wet field conditions and in 1RS.1AL by 4 d under dry field conditions (Table 3). The presence of the 1RS.1DL in Pavon reduced plant height significantly. The presence of 1RS translocations in Pavon background significantly increased shoot biomass by 13% only under wet field conditions (Table 3). Also, grain weight and grain yield of the 1RS translocations increased by 15.7 and 27.6%, respectively, under wet field conditions compared with those of Pavon (Table 3). Pavon and its 1RS translocations were similar for number of spikes per 50 cm, number of grains per spike, and HI, except for 1RS.1AL translocation that had more spikes and higher HI than Pavon under wet field conditions (Table 3). The superior performance of the 1RS translocations over Pavon in grain production under wet field conditions appeared to be mainly due to their heavier grains. Villareal et al. (1996) also reported a longer grain filling period and heavier grains for different 1RS.1AL translocations compared with their respective checks. Grain yield of the 1RS translocations also were greater than that of the commercial check Yecora Rojo under well-watered field conditions (Table 3).
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The correlation coefficients between shoot biomass at anthesis and grain weight and grain yield calculated only in 2000 season were not significant, indicating that preanthesis assimilates were not a major source in determining grain yield in that season (Ehdaie and Waines, 1996).
The STI measured for the genotypes based on grain yield and kernel weight are presented in Table 4. The growing season was longer in 2000 than in 1999. The grain filling period in 2000 coincided with partly cloudy days and less heat. Therefore, environmental stresses were less in 2000 than in 1999. On average, drought significantly (P < 0.01) reduced grain yield by 68% and kernel weight by 30% in 1999. In 2000, the two traits also were significantly (P < 0.01) reduced under droughted field conditions by 38 and 34%, respectively. The grain yield-based STI and kernel weight-based STI are measures of relative overall and postanthesis stress tolerance, respectively (Bruckner and Frohberg, 1987). Pavon had consistently low STI, confirming previous reports that this cultivar was susceptible to drought (Calhoun et al., 1994; Bruckner and Frohberg, 1987). The STI values for Yecora Rojo were relatively low, except for grain weight-based STI in the 2000 growing season. The original translocation 1RS.1BL in Kavkaz wheat showed consistent and relatively moderate values for STI (Table 4). In contrast, the STI values for translocation 1RS.1BL in Pavon wheat were not consistent across both years. Since both 1RS.1BL translocations in our study used the same 1RS rye segment, it appears that enhanced adaptability reported for certain 1RS.1BL translocations is the result of complex gene interactions between genes in the 1RS rye chromosome and genes of the recipient wheat cultivar. In the more stressful environments of 1999, the 1RS.1DL and 1RS.1BL translocations exhibited, respectively, greater overall and postanthesis tolerance to drought than Pavon (Table 4). In the less stressful environments of 2000, the overall tolerance of 1RS.1BL and 1RS.1AL translocations and postanthesis tolerance of 1RS.1DL translocation were greater than those of Pavon. The 2RS.2BL and 2BS.2RL translocations had lower values for STI compared with their respective checks (Table 4), indicating that these Blanco rye translocations in Pavon wheat were not beneficial for either yield potential or tolerance to stress environments. In contrast to the 2BS.2RL translocation in the present study, the 2AS.2RL translocation in our previous studies (Lahsaiezadeh et al., 1983; Ehdaie et al., 1991, 1998) showed positive effects on WUE and on field performance, although different bread wheat and rye cultivars (Chinese Spring wheat and Imperial rye) were used to develop these translocations.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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The CIMMYT-derived wheats such as Yecora Rojo and Pavon in the present study and ‘Anza’ and ‘Chenab 70’ in our previous study (Ehdaie et al., 1991) showed relatively small root biomass compared with some landrace wheats. This may be a general phenomenon of some CIMMYT-derived wheats selected under high irrigation and fertilizer inputs. It may be possible to increase grain yield in CIMMYT-type wheats by also selecting for a larger root system. Root biomass is under genetic control with a relatively high heritability under both well-watered and droughted conditions (Ehdaie et al., 2001). A wheat ideotype should react positively to drought by producing a larger root biomass under droughted compared with favorable conditions. The translocation lines examined here did not exhibit this root response. It appeared that presence of the 1RS translocation in the genetic background of Pavon enhanced root biomass only under well-watered conditions. The increased yield potential of certain 1RS.1BL translocations reported in the literature (Rajaram et al., 1983; Villareal et al., 1991, 1995; Moreno-Sevilla et al., 1995a) may be due to their greater root biomass and the observed higher transpiration rate. The promising yield performance reported for the 1RSK translocations in Pavon suggest that additional translocations involving the other rye chromosomes should be systematically developed and tested in a common wheat background in gravimetric pot and field studies.
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ACKNOWLEDGMENTS |
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Received for publication February 21, 2002.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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based on grain yield and kernel weight for bread wheat ‘Pavon’, its 1RS, 2RS.2BL and 2BS.2RL translocation lines and their respective checks 2B1 and 2B2, along with the 1RS.1BLK (‘Kavkaz’ wheat), and ‘Yecora Rojo’ in 1999 and 2000.