Agronomy Journal 94:96-101 (2002)
© 2002 American Society of Agronomy
ROOT DEVELOPMENT
Root Morphology of Contrasting Maize Genotypes
Carlos Costaa,
Lianne M. Dwyerb,
Xiaomin Zhouc,
Pierre Dutilleulc,
Chantal Hameld,
Lana M. Reidb and
Donald L. Smith*,c
a Dep. of Plant Sci., McGill Univ., Macdonald Campus, 21,111 Lakeshore, Ste-Anne-de-Bellevue, QC, H9X 3V9, Canada, and Univ. of Passo Fundo, Passo Fundo, RS, 99001-970, Brazil
b Agric. and Agri-Food Canada, Ottawa, ON, K1A 0C6, Canada
c Dep. of Plant Sci., McGill Univ., Macdonald Campus, 21,111 Lakeshore, Ste-Anne-de-Bellevue, QC, H9X 3V9, Canada
d Dep. of Nat. Resource Sci., McGill Univ., Macdonald Campus, 21,111 Lakeshore, Ste-Anne-de-Bellevue, QC, H9X 3V9, Canada
* Corresponding author (dsmith{at}macdonald.mcgill.ca)
 |
ABSTRACT
|
|---|
Image analysis has greatly simplified the measurement of root systems, allowing more detailed and accurate assessment of standard root variables. However, maize (Zea mays L.) root morphology has primarily been studied in conventional hybrids. We tested the hypothesis that genotypes carrying the leafy trait (taller plants with more leaves and greater leaf area development) would have root morphologies differing from those of conventional maize hybrids. A 3 x 3 factorial experiment was arranged in a randomized complete block design with three blocks, three fertilization levels (0, 127.5, and 255 kg N ha-1 as NH4NO3), and three maize genotypes [leafy reduced stature (LRS), leafy normal stature (LNS), and a conventional commercial hybrid Pioneer 3905 (P3905)]. The genotypes were selected for their contrasting canopy and root architectures. Plants were grown in 63-L plastic containers, and the roots were measured at the silking stage (80 d from emergence) by scanner-based image analysis. In general, greater root length and root surface areas were obtained at an N fertilization rate of 127.5 kg N ha-1 compared with either the absence of fertilizer N or the higher rate of 255 kg N ha-1. For all genotypes, 95% of root length was comprised of roots ranging from 0.20 to 0.40 mm in diameter. Total root length (4 km) and total root surface area (3.2 m2) were similar for LNS and LRS genotypes and were greater than those of P3905 (1.4 km total root length and 1.1 m2 surface area). Root diameter did not differ among genotypes.
Abbreviations: LAI, leaf area index • LNS, leafy normal stature • LRS, leafy reduced stature • P3905, Pioneer 3905
|
INTRODUCTION
|
|---|
ROOT MORPHOLOGY is influenced by the amount of N fertilizer applied (Eghball et al., 1993) and factors such as temperature (Stamp, 1984; Feil et al., 1991) and soil mechanical impedance (Bengough and Mullins, 1990). Eghball et al. (1993) showed that N stress in maize reduced root branching. Similarly, Maizlish et al. (1980) showed greater root branching in maize with increasing levels of applied fertilizer N. Tennant (1976) showed greater root length with increasing levels of applied fertilizer N.
Most studies on roots have focused on their morphology and topology (e.g., Hackett and Rose, 1972; Fitter, 1982). Root characteristics such as length, mean diameter, surface area, and mass have been used to quantitatively and qualitatively describe root systems; however, comparisons made based on length rather than mass generally show greater differences (Box and Ramseur, 1993). Several methods have been used to estimate root length (Rowse and Phillips, 1974; Richards et al., 1979; Zoon and Van Tienderen, 1990). The most widely employed methods are based on the line intersect principle, which was first devised by Newman (1966) and later modified (Marsh, 1971; Tennant, 1975). Because this method relies on visual counting of grid line–root intercepts, it can be time consuming and prone to inaccuracy, especially when measuring samples with a large proportion of fine roots (Smit et al., 1994). However, the line intercept method improved root measurement and, in particular, reduced the time required for analysis compared with simpler, manual methods. For example, the measurement of 3.43 m of roots took 24 min using the line intercept method, whereas 67 min were required with the manual method (Newman, 1966). Scanner-based, computer-assisted image analysis has made the measurement of root characteristics faster, more accurate, and less subjective than previous methods (Collins et al., 1987; Cunningham et al., 1989; Stutte et al., 1995; Box, 1996). Despite these technological advances in root study, root length measurement is still time consuming, mainly because of the potentially great length of a single root system. For example, Pavlychenko (1937) reported a length of 87.4 km for a single root system of wild oat (Avena sativa L.) grown free of competition, and Dittmer (1937) reported a 622.8-km length for a single 80-d-old winter rye (Secale cereale L.) plant.
Excluding our own work on root sampling method (Costa et al., 2000), studies on maize root morphology have yet to include leafy genotypes. These new genotypes include leafy reduced stature [Lfy1 rd1] (LRS) and leafy normal stature [Lfy1 Rd1] (LNS) where leafy is a dominant trait and reduced stature a recessive one. Leafy inbreds differ in canopy architecture from conventional genotypes by having a greater number of above-ear leaves (Shaver, 1983) and, on average, two more leaves than nonleafy genotypes (Modarres et al., 1998), resulting in a higher leaf area index (LAI) (Stewart and Dwyer, 1993, 1999; Modarres et al., 1998; Begna et al., 1999). Genotypes carrying the leafy trait also have a shorter vegetative period, longer grain-filling period, and higher yields than conventional genotypes (Begna et al., 1997, 1999). Preliminary field observations suggested that root systems of genotypes containing the leafy trait were more extensive, branched more, and showed a greater proportion of fine roots than their conventional counterparts (A.M. Modarres and D.L. Smith, personal communication, 1996).
Our objectives were to determine the effects of applied N fertilizer on measured root characteristics of contrasting maize genotypes (LRS, LNS, and conventional maize hybrid P3905).
|
MATERIALS AND METHODS
|
|---|
Plant Material
Three maize genotypes (LRS, LNS, and P3905) were used in this study because of their contrasting canopy architectures (Stewart and Dwyer, 1993, 1999), aboveground morphological characteristics (Modarres et al., 1997; Dijak et al., 1999; Begna et al., 1997), and root morphologies (Costa et al., 2000), which had been assessed, at least to some degree, in previous indoor and field studies. The LRS is derived from (W117rd/CM174rd1) CO392 and the LNS from (W117rd/CM174rd1) CO422Lfyl; both were developed by Agriculture and Agri-Food Canada, Ottawa, ON, Canada.
Growth Conditions
Plants were grown to the silking stage in containers (0.43m top diameter, 0.33 m bottom diameter and 0.56 m high) filled with a soil/sand mixture (2:1 v/v) in the research greenhouse of the Macdonald Campus of McGill University, Ste-Anne-de-Bellevue, QC, Canada. The soil material was collected from the top 0.10 m of soil at a local site. The soil was a Courval sandy soil (fine-silty, mixed, nonacid, frigid Humaquept). A randomized complete block design with three blocks was used in which treatments consisted of three N levels (equivalent to 0, 127.5, and 255 kg N ha-1 as NH4NO3) factorially combined with three genotypes (LRS, LNS, and P3905).
Four seeds were sown per container, and the resulting seedlings were thinned to one per container 3 d after emergence. Day and night air temperatures in the greenhouse were 24 and 16 (±2) °C, respectively, and the relative humidity was 85%. A light–dark regime of 16 and 8 h, respectively, was maintained at a lighting level of 470 µmol m-2 s-1 with Philips 430-W high pressure sodium lamps (Philips Electronics, Ontario, Canada). Light intensity was monitored with a 1-m-long quantum sensor bar (LI 190SB, LI-COR, Lincoln, NE).
At silking, plants were removed from the containers by carefully sliding out the entire root mass. The stem was cut off and the root system washed. The roots were first completely immersed in a water-filled container and then sprayed with water until almost free of soil and sand. Sieves of several mesh sizes (2 mm and 500 and 53 µm) were used to prevent the loss of fine roots. Root systems that were not analyzed immediately were kept fully immersed in a 4% (w/v) formaldehyde (CH2O) solution.
Measurement of Root Characteristics
The methods we used to obtain a representative subsample of the large root systems existing at silking are fully detailed in Costa et al. (2000). Obtaining homogeneous subsamples required four steps: (i) cutting each complete root system into pieces of 
10 mm in length; (ii) staining the root segments [0.1% (w/w) of toluidine blue for 15 min]; (iii) placing the stained root segments into an 18-L, water-filled mixing device; and (iv) fishing out 3-g root segment subsamples with a dip net (Costa et al., 2000). Representative subsamples of 0.5 g were collected, and any remaining material was returned to the mixing system. This process was continued until all subsamples had been processed. Each 0.5-g root subsample was placed in a Plexiglas tray for measurement. Previous work had shown that root subsamples of LRS, LNS, and P3905 hybrids amounting to 14, 4, and 10% (fresh wt. basis) of their entire root systems, respectively, were required to accurately (10% level of precision) estimate root length, surface area, and mean diameter of entire root systems (Costa et al., 2000).
Measurement of the root samples was performed with WinRHIZO version 3.9 (Regent Instruments, Quebec, Canada) (www.regent.qc.ca; verified 30 Aug. 2001), an interactive scanner-based image analysis system. This proprietary system for root measurement allowed the control of scanning imaging acquisition processes and of subsequent image analysis. Root samples were placed in the Plexiglas tray (0.2 by 0.3 m) in 3 to 4 mm of water, and roots were untangled with a plastic spatula to minimize overlapping. The tray was placed on a Hewlett Packard ScanJet 3c/T optical scanner (Hewlett Packard, Palo Alto, CA) set to a scanning resolution of 300 dpi [dots per inch (25.4 mm)] and linked to a Windows-based PC. The scanner had two lightning sources, one located above (on the scanner cover) and another below (incorporated in the main body of the scanner). The images were scanned through the WinRHIZO system.
Statistical Analyses
Statistical analyses were performed on the root morphological characteristics measured with the scanner-based image analysis system using SAS Release 6.12 for Windows (SAS Inst., 1997). The SAS procedures used for the ANOVA and normality tests were GLM and UNIVARIATE, respectively. Protected ANOVA tests of LSD were used to assess the differences between treatment means (Steel and Torrie, 1980). Regression analysis was carried out with SAS procedure REG (SAS Inst., 1997).
|
RESULTS AND DISCUSSION
|
|---|
Response of Genotypes to Applied Nitrogen Fertilization Rates
Overall, greater root length and root surface area were obtained at an N fertilization rate of 127.5 kg N ha-1 compared with either the absence of fertilizer N or a higher fertilization rate of 255 kg N ha-1 (Fig. 1)
. These results concur with most reports on the effects of N fertilization rate on root characteristics (Drew et al., 1973; Tennant 1976). A N x hybrid interaction occurred for root length and surface area, with different genotype rankings occurring from one N rate to another. Whereas LRS had the greatest mean values of length and surface area at 127.5 kg N ha-1, LNS had greater root length and surface area at 0 and 255 kg N ha-1 than at 127.5 kg ha-1. This suggests different genotypic responses to environmental constraints and indicates that LNS might be more tolerant to N availability extremes than either LRS or P3905.
View larger version (26K):
[in this window]
[in a new window]
|
Fig. 1. Root length and surface area of maize genotypes under three rates of N fertilization. Genotypic means of a root variable followed by a different letter are declared to be different from each other (P  0.05) by an ANOVA-protected LSD test. LRS, leafy reduced stature; LNS, leafy normal stature; and P3905, Pioneer 3905.
|
|
Total root length and surface area varied among the three maize genotypes (Fig. 1). For LNS and LRS genotypes, total root length (4 km) and total root surface area (3.2 m2) were similar but were 2.9- and 3.3-fold (P < 0.05) greater than those of P3905 (Fig. 1). Given the containers in which they were grown, these measured root lengths were equivalent to densities of 66.5 (LRS), 62.4 (LNS), and 22.2 m dm-3 (P3905). The greater root length of LRS is consistent with results of a separate study, including only LRS and P3905, carried out both indoors and in field experiments (data not shown). In that case, the root length of LRS was 1.13-fold greater than that of P3905 when grown indoors but 1.20-fold greater in mature field-grown plants. Previous field observations had inferred that root systems of leafy-type plants were longer and presumably more diffuse and robust than those of conventional hybrids (A.M. Modarres, personal communication, 1996). Greater root lengths of genotypes bearing the leafy trait (LRS and LNS), compared with those of conventional hydrids, might indicate the influence of their genotypic differences, as reflected in their water and solute uptake abilities (Cowan, 1965; Brewster and Tinker, 1970). Although not comparable, root lengths found in this study are similar to those reported elsewhere for outdoor experiments (Dittmer, 1937; Pavlychenko, 1937).
Root dry mass and root/shoot ratio varied among the applied N fertilizer rates and were greater at the moderate N rates (Fig. 2)
than at either of the other rates. At the 127.5 kg N ha-1 fertilization rate, root dry matter was 1.57- and 1.86-fold greater and root specific dry mass 1.30 and 1.88-fold greater, respectively, than at 0 or 255 kg N ha-1 (Fig. 2). The positive effect of N on root dry matter has been previously documented (Eghball et al., 1993). Genotypes did not rank in the same order for these aboveground variables as they did for root morphological characteristics, with LNS showing both greater dry mass and root/shoot ratio than LRS or the conventional commercial counterpart P3905 (data not shown). For instance, the measured root dry mass of LNS was 1.9-fold greater than that of P3905.
View larger version (18K):
[in this window]
[in a new window]
|
Fig. 2. Across-genotype means of root dry mass and root/shoot ratio for three rates of N fertilization for maize grown to silking. Means of a root variable followed by a different letter are declared to be different from each other (P 0.05) by an ANOVA-protected LSD test.
|
|
Comparison of Complete and Sampling Methods
Total root lengths of LRS, LNS, or P3905 plants were obtained either by (i) measuring the entire root system (423, 362, or 172 subsamples of 0.5 g of fresh mass each) or (ii) sampling the root system (subsamples making up 10% of total root material, multiplied by 10) and were categorized within different root diameter ranges (Fig. 3)
. Total root length did not differ (P > 0.05) between the sampling and whole root-system approaches (Fig. 3). A close agreement in total root length between sampling and entire root-system measurement approaches was also reported for P3905 (Costa et al., 2000).
View larger version (23K):
[in this window]
[in a new window]
|
Fig. 3. Distribution of total root length of maize over 10 root diameter ranges for three maize genotypes grown to silking for the sampling and entire root-measurement approaches. Bars represent ± standard error. LRS, leafy reduced stature; LNS, leafy normal stature; and P3905, Pioneer 3905.
|
|
Frequency Distribution of Roots among Root Diameter Classes
The image analysis system used for measuring roots allowed for the classification of roots into ranges of root diameter. The frequency distribution of root length among root diameter ranges was similar for all genotypes; most root length was contributed by roots from 0.20 to 0.40 mm in diameter (Fig. 4)
. In this study, we used 10 diameter ranges from 0.00 to 1.00 mm in 0.10-mm increments (Fig. 4). Bohm (1979) recognized six root diameters: very fine (<0.5 mm), fine (0.5–2 mm), small (2–5 mm), medium (5–10 mm), large (10–20 mm), and very large (>20 mm). In our work, very fine roots represented the majority of measured roots of the maize genotypes included in this study (Fig. 4). Roots having a diameter <0.5 mm comprised 96 to 98% of total measured roots. At 98%, LRS had the largest proportion of very fine roots. This result is in agreement with other reports for maize genotypes. For example, Pallant et al. (1993) reported 70% for fine roots of maize. Cahn et al. (1989) found that 98% of lateral roots of maize grown for 5 wk in minirhizotrons were <0.6 mm indiameter. However, in our study, roots were not quantified separately accordingly to their categories (core, nodal, or lateral roots). When the genotypes studied were compared on the basis of roots <0.10 mm in diameter, LRS had nearly 45%, LNS 43%, and P3905 41% (Fig. 4). This high proportion of extremely fine roots stresses the need for great care in measuring maize root systems because such roots are often underestimated when using image analysis, given the system's inability to detect them due to their small diameter and near transparency (Burke and LeBlanc, 1988). Mean root diameters (0.25, 0.26, and 0.27 mm for LRS, LNS, P3905, respectively) were not significantly different.
View larger version (28K):
[in this window]
[in a new window]
|
Fig. 4. Percent distribution of total root length of maize over 10 root diameter ranges for genotypes grown to silking. LRS, leafy reduced stature; LNS, leafy normal stature; and P3905, Pioneer 3905.
|
|
Relationship of Root Dry Mass to Root Length
Total root length was linearly correlated to the total root dry mass for pooled data of the three genotypes (not shown) and for each individual hybrid (Fig. 5)
, confirming findings reported elsewhere (Carley and Watson, 1966; Murphy and Smucker, 1995). However, the specific relationship varied among genotypes. Root mass is easier to measure than length (Carley and Watson, 1966; Murphy and Smucker, 1995). Our findings indicate that one could obtain reasonable estimates of total length by simply measuring root weight.
View larger version (15K):
[in this window]
[in a new window]
|
Fig. 5. Relationship between total fresh root length and root dry mass of maize genotypes grown indoors to silking. LRS, leafy reduced stature; LNS, leafy normal stature; and P3905, Pioneer 3905.
|
|
The mean root diameter was greater in the absence of N application than at a rate of 127.5 or 255 kg N ha-1 (Fig. 6)
. This finding contradicts the general observation that finer-diameter roots are formed under low N regimes (Fitter, 1996). However, the length of roots with very fine diameter (<0.10 mm) was greater in LRS and LNS than the conventional genotype. This concurs with findings that the root diameter distribution tends to determine the total root length that a plant can produce (Fitter, 1985).
View larger version (21K):
[in this window]
[in a new window]
|
Fig. 6. Mean root diameter across genotypes for three different rates of N fertilization. Genotypic means of a root variable followed by a different letter are declared to be different from each other (P 0.05) by an ANOVA-protected LSD test.
|
|
|
CONCLUSIONS
|
|---|
Genotypes bearing the leafy trait had greater root lengths and surface areas than the conventional hybrid. This confirms previous field observations suggesting more extensive and branched root systems for the LRS maize genotypes. The rate of applied N greatly affected root characteristics. Overall, greater root length and root surface area were obtained at an N fertilization rate of 127.5 kg N ha-1 compared with either the absence of fertilizer N or at an N rate of 255 kg N ha-1. The sampling procedure used in this study could substitute for the measurement of an entire large root system.
|
ACKNOWLEDGMENTS
|
|---|
The authors acknowledge the technical assistance of Michiei Sho, Teshome Melkamu, Visay Linn, Line Nantais, and Stewart Leibovitch and are grateful for comments of Georges T. Dodds. This research was supported by Agriculture and Agri-Food Canada, Matching Investment Initiative, and an NSERC Collaborative Research Grant. The senior author is grateful to the Brazilian Post-Graduate Agency (CAPES) for financial support.
|
REFERENCES
|
|---|
- Begna, S.H., R.I. Hamilton, L.M. Dwyer, D.W. Stewart, and D.L. Smith. 1997. Effects of population density and planting pattern on the yield and yield components of leafy reduced-stature maize in a short-season area. J. Agron. Crop Sci. 179:9–17.
- Begna, S.H., R.I. Hamilton, L.M. Dwyer, D.W. Stewart, and D.L. Smith. 1999. Effects of population density on vegetative growth of leafy reduced-stature maize in short-season areas. J. Agron. Crop Sci. 182:49–55.
- Bengough, A.G., and C.E. Mullins. 1990. Mechanical impedance to root growth: A review of experimental techniques and root growth responses. J. Soil Sci. 41:341–358.
- Bohm, W. 1979. Methods of studying root systems. Springer-Verlag, Berlin.
- Box, J.E. 1996. Modern methods for root investigations. p. 193–237. In Y. Waisel, A. Eshel, and U. Kafkafi (ed.) Plant roots: The hidden half. Marcel Dekker, New York.
- Box, J.E., and E.L. Ramseur. 1993. Minirhizotron wheat root data: Comparisons to soil core root data. Agron. J. 85:1058–1060.[Abstract/Free Full Text]
- Brewster, J.L., and P.B. Tinker. 1970. Nutrient cation flows in soil around plant roots. Soil Sci. Am. J. Proc. 34:421–426.
- Burke, M.K., and D.C. LeBlanc. 1988. Rapid measurement of fine root length using photoelectronic image analysis. Ecology 69:1286–1289.
- Cahn, M.D., R.W. Zobel, and D.R. Bouldin. 1989. Relationship between root elongation rate and diameter and duration of growth of lateral roots of maize. Plant Soil 119:271–279.
- Carley, H.E., and R.D. Watson. 1966. A new gravimetric method for estimating root-surface areas. Soil Sci. 102:289–291.
- Collins, R.P., P.J. Gregory, H.R. Rowse, A. Morgan, and B. Lancashire. 1987. Improved methods of estimating root length using a photocopier, a light box and a bar code reader. Plant Soil 103:277–280.
- Costa, C., L.M. Dwyer, R.I. Hamilton, C. Hamel, L. Nantais, and D.L. Smith. 2000. A sampling method for measurement of large root systems with scanner-based image analysis. Agron. J. 92:621–627.[Abstract/Free Full Text]
- Cowan, I.R. 1965. Transport of water in the soil–plant–atmosphere system. J. Appl. Ecol. 2:221–239.
- Cunningham, M., M.B. Adams, R.J. Luxmoore, W.M. Post, and D.L. DeAngelis. 1989. Quick estimates of root length, using a video image analyzer. Can. J. For. Res. 19:335–340.
- Dijak, M., A.M. Modarres, R.I. Hamilton, L.M. Dwyer, D.W. Stewart, D.E. Mather, and D.L. Smith. 1999. Leafy reduced-stature maize hybrids for short-season environments. Crop Sci. 39:1106–1110.[Abstract/Free Full Text]
- Dittmer, H.J. 1937. A quantitative study of the roots and root hairs of a winter rye plant (Secale cereale). Am. J. Bot. 24:417–420.[Web of Science]
- Drew, M.C., L.R. Saker, and T.W. Ashley. 1973. Nutrient supply and the growth of the seminal root system in Barley. J. Exp. Bot. 24:1189–1202.[Abstract/Free Full Text]
- Eghball, B., J.R. Settimi, J.W. Maranville, and A.M. Parkhurst. 1993. Fractal analysis for morphological description of corn roots under nitrogen stress. Agron. J. 85:287–289.[Abstract/Free Full Text]
- Feil, B., R. Thirapon, G. Geisler, and P. Stamp. 1991. The impact of temperature on seedling root traits of European and tropical corn (Zea mays L.) cultivars. J. Agron. Crop Sci. 166:81–89.
- Fitter, A. 1996. Characteristics and functions of root systems. In Y. Waisel, A. Eshel, and U. Kafkafi (ed.) Plant roots: The hidden half. Marcel Dekker, New York.
- Fitter, A.H. 1982. Morphometric analysis of root systems: Application of the technique and influence of soil fertility on root system development in two herbaceous species. Plant Cell Environ. 5:313–322.
- Fitter, A.H. 1985. Functional significance of root morphology and root system architecture. In A.H. Fitter, D. Atkinson, D.J. Read, and M.B. Usher (ed.) Ecological interactions in soil. Blackwell Scientific, Oxford.
- Hackett, C., and D.A. Rose. 1972. A model of the extension and branching of a seminal root of barley and its use in studying relations between root dimensions: I. The model. Aust. J. Biol. Sci. 25:669–679.
- Maizlish, N.A., D.D. Fritton, and W.A. Kendall. 1980. Root morphology and early development of maize at varying levels of nitrogen. Agron. J. 72:25–30.[Abstract/Free Full Text]
- Marsh, B.a'B. 1971. Measurement of length in random arrangements of lines. J. Appl. Ecol. 8:265–267.
- Modarres, A., R.I. Hamilton, M. Dijak, L.M. Dwyer, D.W. Stewart, D.E. Mather, and D.L. Smith. 1998. Plant population density effects on maize inbred lines grown in short-season environments. Crop Sci. 38:104–108.[Abstract/Free Full Text]
- Modarres, A.M., R.I. Hamilton, L.M. Dwyer, D.W. Stewart, D.E. Mather, M. Dijak, and D.L. Smith. 1997. Leafy reduced-stature maize for short-season environments: Morphological aspects of inbreds lines. Euphytica 96:301–309.
- Murphy, S.L., and A.J.M. Smucker. 1995. Evaluation of video image analysis and line-intercept methods for measuring root systems of alfalfa and ryegrass. Agron. J. 87:865–868.[Abstract/Free Full Text]
- Newman, E.I. 1966. A method of estimating the total root length in a sample. J. Appl. Ecol. 3:139–145.
- Pallant, E., R.A. Holmgren, G.E. Schuler, K.L. McCracken, and B. Drbal. 1993. Using a fine root extraction device to quantify small diameter corn roots (> 0.025 mm) in field soils. Plant Soil 153: 273–279.
- Pavlychenko, T.K. 1937. Quantitative study of the entire root systems of weed and crop plants under field conditions. Ecology 18:62–79.[Web of Science]
- Richards, D., F.H. Goubran, W.N. Garwoli, and M.W. Daly. 1979. A machine for determining root length. Plant Soil 52:69–76.
- Rowse, H.R., and D.A. Phillips. 1974. An instrument for estimating the total length of root in a sample. J. Appl. Ecol. 11:309–314.
- SAS Institute. 1997. SAS for Windows. Release 6.12. SAS Inst., Cary, NC.
- Shaver, D.L. 1983. Genetics and breeding of maize with extra leaves above the ear. p. 161–180. In Proc. Annu. Corn and Sorghum Industry Res. Conf., 38th, Chicago, IL. 7–8 Dec. 1983. Am. Seed Trade Assoc., Washington, DC.
- Smit, A.L., J.F.C.M. Sprangers, P.W. Sablik, and J. Groenwold. 1994. Automated measurement of root length with a three-dimensional high-resolution scanner and image analysis. Plant Soil 158:145–149.
- Soddell, J., and R. Seviour. 1994. A comparison of methods for determining the fractal dimensions of colonies of filamentous bacteria. Binary 6:21–31.
- Stamp, P. 1984. Chilling tolerance of young plants demonstrated on the example of maize (Zea mays L.). In G. Geisler (ed.) Adv. Agron. Crop Sci. 7. Verlag Paul Parey, Berlin.
- Steel, R.G.D., and J.H. Torrie. 1980. Principles and procedures of statistics in biological research. 2nd ed. McGraw-Hill, New York.
- Stewart, D.W., and L.M. Dwyer. 1993. Mathematical characterization of maize canopies. Agric. For. Meteor. 66:247–265.
- Stewart, D.W., and L.M. Dwyer. 1999. Mathematical characterization of leaf shape and area of maize hybrids. Crop Sci. 39:422–427.[Abstract/Free Full Text]
- Stutte, G.W., and E.C. Stryjewski. 1995. Computer classification of roots from digitized video images. HortScience 30:906.[Abstract/Free Full Text]
- Tennant, D. 1975. A test of a modified line intersect method of estimating root length. J. Ecol. 63:995–1101.
- Tennant, D. 1976. Root growth of wheat: I. Early patterns of multiplication and extension of wheat roots including effects of levels of nitrogen, phosphorus and potassium. Aust. J. Agric. Res. 27:183–196.
- Zoon, F.C., and P.H. Van Tienderen. 1990. A rapid quantitative measurement of root length and root branching by microcomputer image analysis. Plant Soil 126:301–308.
This article has been cited by other articles:
|
|
|
|
 
M. Z. Z. Jahufer, S. N. Nichols, J. R. Crush, L. Ouyang, A. Dunn, J. L. Ford, D. A. Care, A. G. Griffiths, C. S. Jones, C. G. Jones, et al.
Genotypic Variation for Root Trait Morphology in a White Clover Mapping Population Grown in Sand
Crop Sci.,
March 19, 2008;
48(2):
487 - 494.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. Qin, P. Stamp, and W. Richner
Impact of Tillage and Banded Starter Fertilizer on Maize Root Growth in the Top 25 Centimeters of the Soil
Agron. J.,
April 27, 2005;
97(3):
674 - 683.
[Abstract]
[Full Text]
[PDF]
|
|
|
TOP
ABSTRACT
INTRODUCTION
