Crop Science 41:1401-1405 (2001)
© 2001 Crop Science Society of America
CROP BREEDING, GENETICS & CYTOLOGY
Heritability of Heat Tolerance in Winter and Spring Wheat
Amir M. H. Ibrahim*,a and
James S. Quickb
a Plant Science Dep., South Dakota State Univ., Brookings, SD 57007
b Dep. of Soil and Crop Sciences, Colorado State Univ., Fort Collins, CO 80523
* Corresponding author (amir_ibrahim{at}sdstate.edu)
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ABSTRACT
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Cell membranes are the site for many biological activities of the plant and play a key role in heat-induced damage to wheat (Triticum aestivum L.). This study evaluated the genetic variability of wheat using two assays of heat tolerance, and estimated their heritability by parent-offspring regression, parent-offspring correlation, and realized heritability using F3 plants and their F4 progeny means. One assay of heat tolerance was membrane thermal stability (MTS) which measures electrolyte leakage from leaf tissue after exposure to high temperature. Heat injury was also assessed by quantifying the reduction of triphenyl tetrazolium chloride (TTC) to formazan by mitochondrial dehydrogenase respiratory enzymes in heat-stressed seedlings. Results from the two assays were highly associated (r = 0.62, n = 14, P < 0.05). Parent-offspring regression and correlation heritability was intermediate to high (0.50–0.65) for TTC and relatively low (0.32–0.38) for MTS. Realized heritability, based on 15% selection intensity, was intermediate to high (0.49–0.64) for TTC and low to intermediate (0.27–0.47) for MTS. The high heritability of TTC warrants good progress from selection in early generations. The relatively lower heritability of MTS suggests the use of multiple replications during selection to limit environmental effects.
Abbreviations: MTS, membrane thermal stability • TTC, tetrazolium triphenyl chloride reduction
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INTRODUCTION
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HEAT STRESS, accompanied by drought, during flowering and grain filling stages of wheat reduces grain yield and test weight in the central to southern Great Plains of the USA. Consequently, there is continual demand for heat-tolerant wheat germplasm suited to these areas. Several heat stress related traits have received attention, including stomatal number (Kazemi et al., 1978), stomatal conductance (Jones, 1977), excised-leaf water loss (Clarke and McCaig, 1982), epicuticular waxes (Johnson et al., 1983), photosynthetic rate (Kaul and Crowle, 1974), osmoregulation (Morgan, 1983), stem reserve mobilization (Blum et al., 1994), seed endosperm utilization (Blum and Sinmena, 1994), chlorophyll fluorescence (Moffatt et al., 1990), and canopy temperature depression (Blum et al., 1982).
Recent heat tolerance research is directed to understanding acquired thermal tolerance, which is defined as the ability of the plant to withstand an otherwise lethal heat treatment if it has been pretreated with some appropriate nonlethal heat treatment (Nagao, 1989). One of the faster screening methods is electrolyte leakage from leaves subjected to elevated temperatures (Shanahan et al., 1990). This method measures the increased electrolyte diffusion resulting from heat induced cell membrane permeability. The electrolyte leakage is captured by bathing the heat stressed tissue in deionized water and quantified by electrical conductance measurements. Membrane thermal stability of different genotypes is expressed in terms of electrolytic conductance (Sullivan, 1972; Martineau et al., 1979; Blum and Ebercon, 1981; Saadalla et al., 1990a). Reynolds et al. (1994) obtained positive correlations between MTS values and wheat grain yield in five international locations with high temperatures during the production season.
Heat stress also is quantified by mitochondrial reduction of tetrazolium triphenyl chloride (TTC). Wheat leaf tissue is subjected to the same temperature regime as in the electrolyte leakage assay. Following heat treatment, the TTC solution is vacuum infiltrated into the leaf tissue. The relative level of TTC reduction to formazan quantifies cell viability, by spectrophotometric assay of the red formazan (Towill and Mazur, 1974). This assay directly determines mitochondrial electron transport activity. Porter et al. (1994) used the TTC reduction assay to quantify acquired high temperature tolerance differences in winter wheat cultivars. They reported significant genetic differences in acquired thermal tolerance, and concluded that the TTC assay was an efficient, reliable technique.
Information on the genetic control and mode of inheritance of MTS and TTC reduction traits is scant. Heritability of a trait expresses the reliability of the phenotypic value as a guide to the breeding value and the trait utility within the selection process. Saadalla et al. (1990b) estimated genetic effects for MTS by examining 90 F5 genotypes derived from crosses among heat-tolerant and heat-sensitive wheat parents. They observed transgressive segregation in F5 progeny means of relative injury values determined by MTS tests, suggesting that the parents contributed different genes for heat tolerance and that the trait is not simply inherited. Marsh et al. (1985) found that MTS is controlled by a few genes in common bean. They also reported low estimates of narrow and broad sense heritability, suggesting relatively small additive effects and sizeable environmental effects. Inheritance of thermotolerance was evaluated by Fokar et al. (1998) by the TTC reduction assay. They found that broad sense heritability of TTC measured at the seedling stage was 0.89, suggesting that improvement of heat tolerance can be achieved by selection.
The objectives of this study, therefore, were (i) to determine the genetic variability and association of MTS and TTC assays in a set of 14 diverse spring and winter wheat lines and (ii) to determine the potential of cellular thermostability traits for selection by estimating the heritability of MTS and TTC.
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MATERIALS AND METHODS
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Genetic Variability of Acquired Thermal Tolerance
Fourteen diverse winter and spring wheat lines were evaluated for acquired thermal tolerance as measured by MTS and TTC assays in controlled environment experiments (Table 1). Analysis of variance was conducted with the GLM procedure (SAS Institute, 1989), and means were separated by the least significant difference (LSD). The data were analyzed as a completely randomized design with three replications. The simple linear correlation between MTS and TTC was calculated according to Steel and Torrie (1980).
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Table 1. Acquired thermal tolerance as measured by membrane thermostability (MTS) and triphenyl tetrazolium chloride (TTC) assays for 14 wheat lines. Correlation between MTS and TTC: (r = 0.62, n = 14, P < 0.05).
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Membrane Thermal Stability Assay
Seedlings were grown on moistened, folded germination paper at 20 to 22°C. A dilute solution of Teracoat fungicide (0.15% w:v) was used to water the seedlings daily as needed. The seedlings were transferred after 4 d to a greenhouse with a 16 h photoperiod, a light intensity of 200 uE m-2 s-1, and at about 17°C day and night. Acclimation was started when the first leaf attained about 8 to 10 cm in length (about 8 to 10 d after germination). Seedlings were placed in a water bath with their roots immersed in water (about 1 cm). The water bath was maintained at 39°C for 48 h and covered with transparent plastic to ensure adequate light interception. Following acclimation, 7 cm long leaf segments were excised from 10 seedlings per genotype to form the experimental unit. Leaf segments were rinsed twice in deionized water, and placed in 16 x 150 mm test tubes with 10 mL deionized water. Severe heat stress was applied by submerging tubes to a depth equal to the height of water in the tubes (about 7 cm) in a water bath at 49°C for 30 min. After the treatment period, the tubes were held overnight at room temperature. Conductance was measured with an electrical conductivity meter (Electroanalyzer 4400, Markson Science, Inc., Del Mar, CA) after standardizing it with a 0.005 N KCl solution. Test tubes were then autoclaved for 10 min at 120°C and 0.10 Mpa and conductance was measured again as an indication of the maximum potential leakage from a given sample. Membrane thermal stability was expressed in percentage units as the reciprocal of relative leakage:
where T1 and T2 are the conductivity readings before and after autoclaving, respectively.
TTC Reduction Assay
Eight seeds of each genotype were germinated in moistened, folded germination paper similar to the MTS test. Acclimation was performed as in the MTS test and at the same developmental stage. Immediately following acclimation two sets of two leaves (3.5 cm each) per cultivar were excised, rinsed in deionized water, and each leaf placed in a test tube with 0.1 mL deionized water. The two sets were then heat-treated as follows: the first set was left at 25°C for 90 min, and the second set was placed in a water bath at 49°C for 90 min. Immediately following the 25°C and 49°C treatments, 10 mL of TTC solution (0.8% TTC in 0.05 M NaPO4 buffer, pH 7.4, and 0.5 ml L-1 TWEEN 20) were added per tube and vacuum infiltrated for 10 min. The tissue was incubated in the TTC solution for 24 h at 25°C in the dark. After incubation, leaves were removed and rinsed with distilled water, placed individually in separate spectrophotometric tubes containing 2 mL of 95% ethanol, and submerged for 24 h at 25°C in the dark. The level of acquired high temperature tolerance was determined by measuring the percentage reduction of TTC to formazan using the following formula:
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where ODh refers to the mean optical density (530 nm) values for the heat-stressed set (49°C for 90 min), and ODc refers to the mean optical density for the control set (25°C for 90 min).
Inheritance of Acquired Thermal Tolerance
Two spring wheats, ‘Seri 82’ and ‘Siete Cerros’, and a winter wheat, ‘TAM 108’ were used in this study. TAM 108 and Seri 82 were characterized by many researchers as heat-tolerant while Siete Cerros was characterized as heat-susceptible (Reynolds et al., 1994; Balota et al., 1993; and Porter et al., 1994). Two crosses were made between Siete Cerros and each of TAM 108 and Seri 82. The F1 seed were harvested around 15 Mar. 1996 and planted in the field in Fort Collins, CO on 1 Apr. 1996. Seventy-five F1 plants (F2 seed) were harvested on 1 Aug. 1996. The F2 was advanced to the F3 generation by single seed descent (SSD). F2 plants were vernalized between 15 Aug. and 15 Oct. 1996, and 60 F2 plants from each cross were grown between 15 Oct. 1996 and 30 Jan. 1997 to produce F3 seed. The SSD procedure was also used to advance the F3 to F4 generation. For each cross, ten F3 seeds were harvested from each of the 60 F2 plants on 30 Jan. 1997, vernalized until 22 Apr. 1997, and immediately transplanted to the greenhouse. Fifty-nine F4 progenies were produced in the cross Seri 82/Siete Cerros while 51 progenies were produced in the cross TAM 108/Siete Cerros. Each F3 progeny was represented by 10 plants.
The resultant F4 seeds were harvested around 30 Aug. 1997 and germinated 4 d later in folded germination paper. All entries that had poor germination and/or poor seedling vigor were excluded from the two tests. The MTS and TTC assays were made on 12 d old seedlings in November 1997 as described previously. The MTS test was done on 55 entries of the cross Seri 82/Siete Cerros and 45 entries of the cross TAM 108/Siete Cerros. The TTC test was done on 43 entries of the cross Seri 82/Siete Cerros and 39 entries of the cross TAM 108/Siete Cerros. The F3 lines and their F4 progenies were evaluated under the same environmental conditions by hardening and heat treating both generations together in the same water bath.
The results were analyzed as a completely randomized design with two replicates using the GLM procedure of SAS (SAS Institute, 1989). Heritability of MTS and TTC was estimated using parent-offspring regression (b), parent-offspring correlation (r), and realized heritability. In order to compare the three methods, parent-offspring regression heritability values were not adjusted for degree of inbreeding as suggested by Smith and Kinman (1965). Linear regression coefficients (b) were calculated by regressing F4 progeny means (Yi) on F3 parental means (Xi). Standard error (SE) for parent-offspring regression was calculated as follows:
Parent-offspring correlation (r) is equivalent to parent-offspring regression from data coded in terms of standard deviation units (Frey and Horner, 1957). The approximate standard error for parent-offspring correlation was calculated as follows:
Estimates of realized heritability were obtained using the following formula (Guthrie et al., 1984):
where, 
= mean of high F4 lines, 
= mean of low F4 lines, 
= mean of high F3 selections, and 
= mean of low F3 selections, based on 15% selection intensity.
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RESULTS AND DISCUSSION
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Genetic Variability of Acquired Thermal Tolerance
Analysis of variance showed highly significant variation among the 14 lines for MTS and TTC reduction (Table 1). The mean MTS values ranged from 28.4% in Arlin to 76.4% in Kauz, while the TTC values ranged from 20.4% in MTRWA 116 to 82.2% in Kauz. Kauz, TAM 107-R3, and TAM 107 had consistently high values (more tolerance) for both bioassays. TAM 107-R2 and TAM 107-R3 are backcross-derived lines of TAM 107, with the Russian wheat aphid resistance gene Dn4. Almost all genotypes, except for NE92458 and Arlin, ranked similarly for the two bioassays. Although NE92458 and Arlin had the lowest MTS values, their TTC was intermediate. There was a positive association between MTS and TTC (r = 0.62, n = 14, P < 0.05). Similar results were reported by Fokar et al. (1998) who found correlation between MTS and TTC across eight cultivars tested at the seedling and flowering growth stages (r = 0.74–0.75, P < 0.05). Chen et al. (1982) also found MTS and TTC bioassays to give similar ranking for two genotypes each of bean, potato, soybean, and tomato. Several researchers found a high correlation between the seedling and flowering growth stage for MTS and/or TTC (Saadalla et al., 1990b; Balota et al., 1993; and Fokar et al., 1998). These results suggest that both MTS and TTC bioassays can be used to screen genotypes for heat tolerance at the seedling stage in the laboratory.
We cannot conclude that MTS and TTC are under similar genetic control or that they are physiologically associated. Many of these lines were selected based on yield performance under heat-stress conditions, so simultaneous selection for underlying physiological mechanisms controlling both MTS and TTC may have occurred. Fokar et al. (1998) found that some cultivars such as Glennson 82, Bacanora, and V747 were relatively thermostable in terms of both MTS and TTC bioassays, while other cultivars such as Danbata were thermostable for MTS while being intermediate for the TTC assay.
Heritability of Acquired Thermal Tolerance
Mode of inheritance of MTS and TTC assays was studied in two crosses, in which the heat-sensitive cultivar Siete Cerros was used as the female parent and the heat-tolerant cultivars, Seri 82 and TAM 108, were used as male parents. Means and standard errors for F3 and F4 progenies and their parents are shown in Table 2. The heat-tolerant parents, Seri 82 and TAM 108, had consistently higher MTS and TTC values than the heat-sensitive parent Siete Cerros. The F3 and F4 population means were generally intermediate between the parental means for both assays. The F3 and F4 population MTS means were considerably higher than the mean of the heat-sensitive parent, Siete Cerros, but not significantly different from the mean of the heat-tolerant parents, TAM 108 and Seri 82.
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Table 2. Means (±SE) of membrane thermostability (MTS) and tetrazolium triphenyl chloride (TTC) assays for two F3 and F4 wheat populations and their parents.
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Transgressive segregation occurs when phenotypes of a segregating population are outside the range of the parental mean values. It arises from contributions of complementary genes from both parents, and is routinely exploited by plant breeders to select individuals superior to the parents. Positive transgressive segregation occured for MTS in both crosses (Fig. 1a and b). Saadalla et al. (1990b) detected only negative transgressive segregation for MTS in TAM 105/Baca and TAM 105/Vona crosses. No genotype from either cross in their study had lower injury than the heat-tolerant parent (TAM 105). The F3 population mean for TTC, however, was not significantly different from the mean of the heat-sensitive parent in the cross TAM 108/Siete Cerros (Table 2, Fig. 1d). Both crosses exhibited positive and negative transgressive segregation for TTC (Fig. 1c and d). The positive transgressive segregation indicates that these two crosses could be very useful for exploiting the genetic variation of cellular thermal tolerance.
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Fig. 1. Frequency distribution of acquired thermal tolerance as measured by membrane thermostability (MTS) and triphenyl tetrazolium chloride (TTC) assays for two wheat crosses in the F3 and F4 generations.
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Heritability was estimated by parent-offspring regression (b), parent-offspring correlation (r) and realized heritability (h2R) using F3 plants and their F4 family means (Table 3). Parent-offspring regression and correlation generally gave similar heritability estimates. Parent-offspring regression heritability was high (0.59–0.65) for TTC and relatively low (0.32–0.33) for MTS. Parent-offspring correlation heritability also was intermediate to high (0.50–0.64) for TTC and relatively low (0.37–0.38) for MTS. Realized heritability estimates, based on 15% selection intensity, were intermediate to high (0.49–0.64) for TTC and low to intermediate (0.27–0.47) for MTS. Broad-sense heritability of TTC was found to be high (0.89) in wheat (Fokar et al., 1998). The high heritability of TTC in this study indicates that good gain from selection can be expected and that TTC can be effectively selected in early generations. Heritability estimates of MTS were lower than those of TTC. However, the heritabilities were sufficient to predict good progress from selection, especially if more replications are used (3 to 5) and if selection is applied in more advanced generations (F4 to F6). The correlations between the two traits in both F3 and F4 generations were not significantly different from zero, indicating that they likely are not genetically or physiologically associated in these populations. Therefore, selection should be applied for both traits to increase the level of heat tolerance in wheat.
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Table 3. Estimates of heritability (±SE) for membrane thermostability (MTS) and tetrazolium triphenyl chloride (TTC) assays in wheat, using parent offspring regression (b), parent offspring correlation (r), and realized heritability (h2R) among F3 plants and their F4 progenies.
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NOTES
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Part of a dissertation submitted by A.M.H. Ibrahim in partial fulfillment of the requirements for a Ph.D. degree in plant breeding and genetics.
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REFERENCES
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- Balota, M., I. Amani, M.P. Reynolds, and E. Acevedo. 1993. Evaluation of membrane thermostability and canopy temperature depression as screening traits for heat tolerance in wheat. Wheat Special Report No. 20. CIMMYT, Mexico, DF.
- Blum, A., and A. Ebercon. 1981. Cell membrane stability as a measure of drought and heat tolerance in wheat. Crop Sci. 21:43–47.
- Blum, A., J. Mayer, and G. Gozlan. 1982. Infrared thermal sensing of plant canopies as a screening technique for dehydration avoidance in wheat. Field Crops Res. 5:137–146.
- Blum, A., and B. Sinmena. 1994. Wheat seed endosperm utilization under heat stress and its relation to thermotolerance in the autotrophic plant. Field Crops Res. 37:185–191.
- Blum, A., B. Sinmena, J. Mayer, G. Golan, and L. Shpiler. 1994. Stem reserve mobilization supports wheat-grain filling under heat stress. Aust. J. Plant Physiol. 21:771–781.
- Chen, T.H.H., Z.Y. Shen, and P.H. Li. 1982. Adaptability of crop plants to high temperature stress. Crop Sci. 22:719–725.[Abstract/Free Full Text]
- Clarke, J.M., and T.N. McCaig. 1982. Excised leaf water retention. Capability as an indicator of drought resistance of Triticum genotypes. Can. J. Plant Sci. 62:571–578.
- Falconer, D.S. 1989. Introduction to quantitative genetics, 3rd ed. John Wiley & Sons, New York.
- Fokar, M., H.T. Nguyen, and A. Blum. 1998. Heat tolerance in spring wheat: I. Genetic variability and heritability of cellular thermotolerance. Euphytica 104(1):1–8.[ISI]
- Frey, K.J., and T. Horner. 1957. Heritability in standard units. Agron. J. 49:59–62.[Abstract/Free Full Text]
- Guthrie, D.A., E.L. Smith, and R.W. McNew. 1984. Selection for high and low grain protein in six winter wheat crosses. Crop Sci. 24: 1097–1100.[Abstract/Free Full Text]
- Johnson, P.A., R.A. Richards, and N.C. Turner. 1983. Yield, water relations, gas exchange, and surface reflectance of near-isogenic lines differing in glaucousness. Crop Sci. 23:318–325.[Abstract/Free Full Text]
- Jones, H.G. 1977. Aspects of water relations of spring wheat (Triticum aestivum L.) in response to induced drought. J. Agric. Sci. 88:267–282.
- Kaul, R., and W.L. Crowle. 1974. An index derived from photosynthetic parameters for predicting grain yields of drought-stressed wheat cultivars. Z. Pflanzensucht. 71:42–51.
- Kazemi, H., S.R. Chapman, and F.H. McNeal. 1978. Variation in stomatal number in spring wheat cultivars. Cereal Res. Commun. 6:359–365.
- Marsh, L.E., D.W. Davis, and P.H. Li. 1985. Selection and inheritance of heat tolerance in the common bean by use of conductivity. J. Am. Soc. Hort. Sci. 110:680–683.
- Martineau, J.R., J.E. Specht, J.H. Williams and C.Y. Sullivan. 1979. Temperature tolerance in soybeans. I. Evaluation of a technique for assessing cellular membrane thermostability. Crop Sci. 19:75–78.[Abstract/Free Full Text]
- Moffatt, L.M., R.G. Sears, T.S. Cox, and G.M. Paulsen. 1990. Wheat high temperature tolerance during reproductive growth: II. Genetic analysis of chlorophyll fluorescence. Crop Sci. 30:886–889.[Abstract/Free Full Text]
- Morgan, J.M. 1983. Osmoregulation as a selection criterion for drought tolerance in wheat. Aust. J. Agric. Res. 34:607–614.
- Nagao, R.T. 1989. The heat shock response in plants: Short-term heat treatment regimes and thermotolerance. p. 331–342. In J.H. Cherry (ed.) Environmental Stress in Plants. NATO ASI Series.
- Porter, D.R., H.T. Nguyen, and J.J. Burke. 1994. Quantifying acquired thermal tolerance in winter wheat. Crop Sci. 34:1686–1689.[Abstract/Free Full Text]
- Reynolds, M.P., M. Balota, M.I.B. Delgado, I. Amani, and R.A. Fisher. 1994. Physiological and morphological traits associated with spring wheat yield under hot irrigated conditions. Aust. J. Plant Physiol. 21:717–30.[ISI]
- Saadalla, M.M., J. F. Shanahan, and J.S. Quick. 1990a. Heat tolerance in winter wheat: I. Hardening and genetic effects on membrane thermostability. Crop Sci. 30:1243–1247.[Abstract/Free Full Text]
- Saadalla, M.M., J.S. Quick, and J.F. Shanahan. 1990b. Heat tolerance in winter wheat: II. Membrane thermostability and field performance. Crop Sci. 30:1248–1251.[Abstract/Free Full Text]
- SAS Inst., Inc. 1989. SAS language guide. Release 6.03 ed. SAS Institute Inc., Cary, NC.
- Shanahan, J.F., I.B. Edwards, J.S. Quick, and J.R. Fenwick. 1990. Membrane thermostability and heat tolerance of spring wheat. Crop Sci. 30:247–251.
- Smith, J.D., and M.L. Kinman. 1965. The use of parent-offspring regression as an estimate of heritability. Crop Sci. 5:595–596.[Free Full Text]
- Steel, R.G.D., and J.H. Torrie. 1980. Principles and procedures of statistics. 2nd ed. McGraw-Hill Book Co., New York.
- Sullivan, C.Y. 1972. Mechanisms of heat and drought resistance in grain sorghum and methods of measurement. In N.G.P. Rao and L.R. House (ed.) Sorghum in the seventies. Oxford and IPH publishing Co., New Delhi, India.
- Towill, L.E., and P. Mazur. 1974. Studies on the reduction of 2,3,5-triphenyl tetrazolium chloride as a viability assay for plant tissue culture. Can. J. Bot. 53:1097–1102.
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ABSTRACT
INTRODUCTION
