Crop Science Grow Your Career with CSSA
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Published online 26 August 2005
Published in Crop Sci 45:2060-2067 (2005)
© 2005 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via ISI Web of Science (3)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Gilbert, R. A.
Right arrow Articles by Abouzid, A.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Gilbert, R. A.
Right arrow Articles by Abouzid, A.
Agricola
Right arrow Articles by Gilbert, R. A.
Right arrow Articles by Abouzid, A.
Related Collections
Right arrow Crop Genetics
Right arrow Sugarcane

CROP BREEDING, GENETICS & CYTOLOGY

Agronomic Evaluation of Sugarcane Lines Transformed for Resistance to Sugarcane mosaic virus Strain E

R. A. Gilberta,*, M. Gallo-Meagherb, J. C. Comstockc, J. D. Millerc, M. Jaind and A. Abouzidd

a Univ. of Florida, EREC, 3200 E. Palm Beach Rd., Belle Glade, FL 33430
b Univ. of Florida, Agronomy Dep., Plant Molecular and Cellular Biology Program, and Genetics Institute, P.O. Box 110300, Gainesville, FL 32611
c USDA-ARS, Sugarcane Field Station, 12990 U.S. Hwy. 441, Canal Point, FL 33438
d Univ. of Florida, Agronomy Dep., P.O. Box 110300, Gainesville, FL 32611

* Corresponding author (ragilbert{at}ifas.ufl.edu)


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Genetic transformation of sugarcane (Saccharum spp.) holds promise for increasing yields and disease resistance. However, the tissue culture and transformation process may produce undesirable field characteristics in transgenic sugarcane. The primary objective of this study was to evaluate variability in agronomic characteristics and field disease resistance of sugarcane transformed for resistance to Sugarcane mosaic virus (SCMV) strain E. One hundred plants derived from cultivars CP 84-1198 (n = 82) and CP 80-1827 (n = 18), consisting of independent virus resistant lines VR 1 (n = 14), VR 4 (n = 24), VR 14 (n = 4), and VR 18 (n = 58) were evaluated in Exp. 1. Transgenics derived from CP 84-1198 had significantly greater tonnes of sucrose per hectare (TSH) and significantly lower SCMV disease incidence than those from CP 80-1827 in the plant-cane (PC), first-ratoon (1R), and second-ratoon (2R) crops. Plants from the VR 18 line had significantly greater economic indices and lower SCMV disease incidence than the VR 4 line in all three crops. Phenotypic variation was high in Exp. 1, with tonnes of cane per hectare (TCH) ranging from 26 to 211 and TSH from 3.2 to 28.9 in the PC crop. Agronomic trait variation decreased with increased selection pressure in Exp. 2, evaluating 30 VR 18 lines, with TCH ranging from 70 to 149 and TSH from 8.5 to 19.0 in PC. The large variability in yield characteristics and disease resistance encountered in this study demonstrates the necessity of thorough field evaluation of transgenic sugarcane while selecting genetically stable and agronomically acceptable material for commercial use.

Abbreviations: 1R, first ratoon • 2R, second ratoon • CP, Canal Point • DSI, disease severity index • EREC, Everglades Research and Education Center • KST, kilograms sucrose tonne–1 • PC, plant cane • SCMV, Sugarcane mosaic virus • TCH, tonnes cane ha–1 • TSH, tonnes sucrose ha–1 • VR, virus resistant


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Sugarcane mosaic virus has recently been increasing in frequency and extent in the Everglades Agricultural Area of Florida (Comstock et al., 2000). Sugarcane mosaic virus had devastating effects on the nascent sugarcane industry in Florida in the 1920s (Bourne, 1972). Given the potential damage of SCMV to the $1-billion dollar Florida sugarcane industry, there is concern about the epidemic potential of this disease.

Genetic transformation combined with field selection may increase sugarcane yields and resistance to diseases such as SCMV (Birch, 1996). Previously, genetic transformation has been used to transfer herbicide resistance (Gallo-Meagher and Irvine, 1996; Falco et al., 2000; Leibbrandt and Snyman, 2003) and insect resistance (Arencibia et al., 1999) into sugarcane. Birch and Maretzki (1993) noted that genetic engineering in sugarcane would be a useful tool for reversing single flaws, such as disease susceptibility, in commercial cultivars. Sugarcane may benefit from genetic transformation because its high ploidy level makes traditional breeding programs difficult, while vegetative propagation of sugarcane allows for relatively stable transfer and multiplication of transgenic materials (Gallo-Meagher and Irvine, 1996).

Birch (1996) predicted that new gene technologies would reshape the sugar industry, yet obstacles to their implementation remain. For example, somaclonal variation caused by tissue culture procedures may produce undesirable field characteristics in genetically transformed sugarcane that are not readily identifiable in the laboratory or greenhouse (Lourens and Martin, 1987; Burner and Grisham, 1995; Oropeza and De Garcia, 1996; Sreenivasan and Jalaja, 1998; Arencibia et al., 1999). Burner and Grisham (1995) report significant somaclonal variation in CP 74-383 sugarcane subjected to different propagation procedures. Normal variants increased from the PC to 1R crops, but still totaled <22% of all plants. Lourens and Martin (1987) reported somaclonal variation in two sugarcane cultivars, CP 65-357 and CP 72-356. The frequency of variants and suitability of tissue culture treatments varied between cultivars, and they recommended that the effects of tissue culture on sugarcane be examined on a cultivar by cultivar basis.

The increased genetic variability associated with somaclonal variation may produce beneficial characteristics as well as deleterious ones. Larkin and Scowcroft (1981) identified genetic variability generated by tissue culture as a potential source for plant improvement. They noted that somaclonal variation in sugarcane was easily obtained and affected important yield characteristics. Although somaclonal variation may be used to add desired attributes (e.g., disease resistance) to sugarcane, they cautioned that stringent field testing was necessary to determine the full extent and effect of genetic changes in putatively beneficial somaclones. Liu (1990) reported agronomically useful sugarcane mutants obtained through tissue culture-induced somaclonal variation with greater stalk number, stem length, and sucrose content than the donor plants, and Leal et al. (1996) used somaclonal variation as a source of eyespot disease resistance in sugarcane. Agronomic evaluation of transgene expression changed with tiller generation in tall fescue (Bettany et al., 1998). The authors suggested that selection for the active state of the transgene over several tiller generations may assist in stabilizing gene expression, an approach analogous to selection for disease resistance during several ratoon crops of sugarcane.

Transgene position effects, copy number, and gene silencing mechanisms can also alter expression levels and stability of expression across time. Therefore, it is crucial that agronomic analyses be conducted in the field across several generations to ensure the stability of transgene expression. However, despite its importance, agronomic analyses of transgenic sugarcane generally have been lacking (Falco et al., 2000), or reports have focused on only a single transgenic line (Leibbrandt and Snyman, 2003). Evaluation of multiple transgenic lines is necessary to identify those with the most desirable agronomic characteristics and to verify stable and effective transgene expression. Cober et al. (2003) evaluated transgenic soybean lines for field resistance to white mold, but to our knowledge there are no published reports of field resistance to SCMV in transgenic sugarcane.

Given the large genetic variability inherent with the production of sugarcane transgenics, thorough field evaluations are necessary to identify high-yielding and disease-resistant germplasm. Evaluations need to be performed separately for each transgenic line derived from different sugarcane cultivars, and across several ratoon crops, to determine the level and stability of SCMV resistance.

The objectives of this study were to (i) thoroughly evaluate the extent of genetic variation in agronomic characteristics in transgenic sugarcane derived from two CP parent clones, (ii) determine the stability of SCMV disease resistance through several ratoon crops, and (iii) identify SCMV disease-resistant and high-yielding transgenic accessions for potential cultivar release.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Transformation, Selection, and Regeneration of Transformed Plants
Embryogenic cultures of sugarcane were established as described by Gallo-Meagher et al. (2000). A total of 386 sugarcane plants was regenerated in vitro following biolistic transformation with nptII and an untranslatable form of the SCMV strain E coat protein gene (Ubi-eut). The embryogenic callus cultures were co-bombarded with equimolar concentrations of the two plasmids according to Sanford et al. (1993). The selection and regeneration of transformed plants was done essentially according to Gallo-Meagher and Irvine (1996), except that resistant calli were selected with 15 mg L–1 geneticin and regenerated shoots were rooted on medium containing 45 mg L–1 geneticin. Transformation via particle bombardment with plasmid vectors carrying the kanamycin resistance gene (pKYLX80) and the untranslatable SCMV strain E coat protein gene (Ubi-eut) (Gallo-Meagher, 2004, unpublished data), and the selection regime for primary transgenics was conducted using standard procedures (Gallo-Meagher and Irvine, 1996). The regenerated sugarcane plants with robust root systems were gradually transferred to peat pots containing Metromix 200 (Scotts-Sierra Horticultural Products Company, Marysville, OH) and placed in an environmental growth chamber at 30°C, under incandescent light at a photon flux density of 80 µmol m–2 s–1 with a 16-h photoperiod. Eight- to 12-wk-old plants were transferred to 15-cm-diam. pots and acclimatized in the greenhouse. One such group of 191 putative transgenic sugarcane plants was selected for transfer and further analyses under field conditions.

PCR Analyses
In view of the vegetative growth habit of sugarcane, the transgenic plants were regularly analyzed by PCR for the presence of both the selectable marker gene (nptII) and the transgene (Ubi-eut). The primer pairs used were as follows.



The PCR amplification products for coat protein (800 bp) and nptII (330 bp) were resolved on a 1.2% (w/v) agarose gel and visualized by ethidium bromide staining. Following PCR screening for the presence of both the selectable marker gene and the transgene, 191 transformed plants were initially planted in the field in unreplicated plots at the USDA-ARS Sugarcane Field Station in Canal Point (CP), FL, in November 1999. From these 191 unreplicated plants, 100 were selected for initial field studies in Feb. 2001. Initial selections were performed on the basis of stalk number (at least six mature stalks) and the absence of SCMV infection or other diseases in the field.

Experiment 1
The 100 plants selected at CP were planted at the University of Florida Everglades Research and Education Center (EREC; 26°39' N, 80°38' W) in Belle Glade, FL, on a Lauderhill muck (euic, hyperthermic Lithic Haplosaprist) soil type. These transgenics included 82 plants derived from ‘CP 84-1198’ (Glaz et al., 1994), and 18 plants from ‘CP 80-1827’ (Glaz et al., 1990). There were four VR lines in the experiment. Each VR line represented plants obtained following separate bombardments of callus derived from either leaf rolls (VR 1) or inflorescence tissue (VR 4, 14, and 18). There were 14 VR1 line transgenics and four VR 14 line transgenics (CP 80-1827 parentage), and 24 transgenics of line VR 4 and 58 transgenics of the VR 18 line (CP 84-1198 parentage).

Experiment 1 was planted 14 Feb. 2001 at the EREC in a randomized complete block design with three replications. The experimental site was chosen in part due to the presence of sweet corn (Zea mays L.) in adjacent fields contributing to high SCMV disease pressure in the area. Three control plots of nontransformed CP 80-1827 and CP 84-1198 parents were included in each replicate. Each plot consisted of a single row, 3 m long with 1.5-m spacing between rows and a 1.5-m break between adjacent plots. Experiment 1 was harvested on 9 Jan. 2002 (PC), 16 Jan. 2003 (first ratoon, 1R), and 12 Jan. 2004 (second ratoon, 2R). Field SCMV scores were recorded in June of 2001 (PC), 2002 (1R), and 2003 (2R) as percentage infected plots. The presence of SCMV leaf mottling symptoms in any stool resulted in an SCMV score of 1 for that plot. A field disease severity index (DSI) was calculated (Cober et al., 2003) such that for a given accession,

[1]
Thus, a score of 0 indicates no SCMV field infection and 100 indicates all plots were infected.

Stalks in each plot were counted in August of 2001 (PC), 2002 (1R), and 2003 (2R). A 5-stalk yield random sample was used to calculate cane production. Plant fresh weights were used to determine individual stalk weight (kg stalk–1), and TCH was calculated as the product of stalk number and stalk weight. To determine sucrose concentration (KST, kg sucrose t–1), the harvest random samples were ground and the crusher juice analyzed for Brix and pol. Brix, which is a measure of percentage soluble solids, was measured using a refractometer which automatically corrected for temperature (Meade, 1963). Pol, which is a unitless measure of the polarization of the sugar solution, was measured using a saccharimeter. Sucrose yield (TSH) was calculated as the product of TCH and KST (divided by 1000 to convert kg sucrose to metric tonnes). A theoretical economic index (EI, $ ha–1) was also calculated, which takes into account harvesting, transport, and milling costs associated with TCH (Deren et al., 1995). Negative EI values may result in extremely low-yielding plots, as sucrose yield is insufficient to cover these costs. The economic index is used to evaluate sugarcane genotypes in the CP breeding program, and thus EI was used to rank transgenic clones for selection purposes in this study. All sugarcane in each plot was harvested mechanically in April of 2001 (PC), 2002 (1R), and 2003 (2R), and the resultant regrowth measured as described above for the following ratoon crop. Following 2R harvest, all transgenic sugarcane in Exp. 1 was destroyed in the field according to USDA-APHIS protocols.

Analyses of variance for sugarcane yield components were performed using Proc GLM in SAS (Littell et al., 2002). Separate analyses were conducted. First, data were pooled by progenitor (CP 84-1198 or CP 80-1827) to determine the effect of the parent material. Second, data were pooled by VR line within parent to compare VR lines originating from the same parent. Statistical significance among yield component means was determined using Fisher's protected LSD test at P < 0.05. Proc VARCOMP in SAS (Littell et al., 1996) was performed using the restricted maximum likelihood method to estimate variance components for VR line and error terms for sugarcane yield traits. Nontransgenic control data were removed from the dataset before variance component estimation. Proc GENMOD in SAS (Littell et al., 2002) was used to analyze SCMV disease data as these data were binomially distributed. Significant differences (P < 0.05) in disease resistance means among parents or VR lines were determined using least square means estimates in SAS.

Experiment 2
On the basis of Exp. 1 PC results, 30 accessions from the VR 18 line were replanted in the same field at EREC in a randomized complete block design with four replications on 7 Feb. 2002. Two control plots of the nontransformed CP 84-1198 parent were included in each replicate. Each plot consisted of two rows 4.5 m long with 1.5-m between-row spacing. Plots were scored for SCMV in June of 2002 (PC) and 2003 (1R), and DSI calculated using Eq. [1]. A five-stalk random sample was taken on 16 Jan. 2003 (PC) and 12 Jan. 2004 (1R) from each plot to estimate yields. Stalks were collected in August of 2002 (PC) and 2003 (1R). Plant population, fresh weight, and sucrose yield measurements were performed for PC and 1R as in Exp. 1. Analysis of variance was performed using Proc GLM in SAS (Littell et al., 2002), with statistical significance among means for each accession determined using Fisher's protected LSD test at P < 0.05.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Experiment 1
There were significant differences in agronomic performance between transgenic sugarcane derived from CP 84-1198 vs. CP 80-1827 parental material (Fig. 1) . Transgenic plants derived from CP 84-1198 had 10 to 32% greater stalk number (Fig. 1A) and 4 to 32% greater stalk weight (Fig. 1B) than transgenics derived from CP 80-1827 in the PC, 1R, and 2R crops (stalk weights were not significantly different in the 2R crop). The KST was also significantly greater for plants derived from CP 84-1198 in PC, but this difference was not maintained in 1R and 2R crops (results not shown). Significantly greater plant population and stalk weight in CP 84-1198 transgenics led to significantly greater TCH (Fig. 1C) and TSH (Fig. 1D) in PC (65 and 73% greater, respectively), 1R (both 27% greater), and 2R (20 and 22% greater), compared with CP 80-1827 transgenic materials. The economic index was 30 to 106% greater for CP 84-1198-derived transgenics across crops (Fig. 1E).



View larger version (36K):
[in this window]
[in a new window]
  		Fig. 1. Effect of parent cultivar on transgenic sugarcane from CP 84-1198 vs. CP 80-1827 donor material: (A) stalk number, (B) stalk weight, (C) cane yield (TCH = tonnes cane ha–1), (D) sucrose yield (TSH = tonnes sucrose ha–1), (E) economic index, and (F) Sugarcane mosaic virus disease severity index. Bars with different letters within a crop age are significantly different (P < 0.05).

 
In addition to superior agronomic performance, the CP 84-1198 transgenic clones were more resistant to SCMV than the CP 80-1827 transgenics (Fig. 1F). The proportion of SCMV-infected transgenic plots was two- to three-fold lower for CP 84-1198 derived transgenics (11–15% infection) than for CP 80-1827 transgenics (33–50% infection) across the three crops (Fig. 1F).

Analysis of VR line data revealed significant differences in sugarcane yield traits between lines from the same parent. VR 18 had significantly greater stalk number, TCH, TSH, and EI than VR 4 (CP 84-1198 progenitors), and the VR 14 line had significantly greater stalk number, stalk weight, TCH, TSH, and EI than VR 1 (CP 80-1827 progenitors) in PC, 1R, and 2R crops (Table 1). The VR 18 line had lower SCMV DSIs (10% in PC, 10% in 1R, and 7% in 2R) than the VR 4 line (26% in PC, 26% in 1R, and 19% in 2R). Lines were selected for advancement at the end of the PC crop in Exp. 1. Each VR 1 line accession had EI values lower than the CP 80-1827 nontransgenic control. The VR 4 accessions were rejected because their agronomic performance was inferior to the CP 84-1198 control. The VR 14 line had several accessions with higher EI than CP 80-1827; however, none of these was resistant to SCMV in the field. Only accessions in the VR 18 line satisfied economic, agronomic, and SCMV disease resistance criteria for advancement. VR 18 lines averaged 3.1 (PC) and 4.9 (1R) more TSH than their CP 84-1198 transgenic parents, which translated to 717 (PC) and 1033 (1R) greater $ ha–1 for the VR 18 transgenics (Table 1). Of the 58 VR 18 accessions included in Exp. 1, 46 had EIs superior to CP 84-1198, with 30 of these exhibiting resistance to SCMV in the PC crop (data not shown). These 30 VR 18 accessions were thus selected for Exp. 2.


View this table:
[in this window]
[in a new window]
  		Table 1. Effect of virus resistant (VR) line on transgenic sugarcane yield traits and Sugarcane mosaic virus disease resistance. CP 84-1198 and CP 80-1827 are nontransgenic controls.

 
Phenotypic variation in transgenic accession performance was extremely high in Exp. 1 (Table 1). In PC, stalk weight ranged from 0.64 to 1.82 kg stalk–1, TCH from 26 to 212 t cane ha–1, and TSH from 3.2 to 28.9 mg sucrose ha–1, representing an eight- to nine-fold difference in yield characteristics among clones. In comparison, the commercial checks varied from 1.2 to 1.9 kg stalk–1, 82 to 163 t cane ha–1, and 10.5 to 21.4 t sucrose ha–1, representing a two-fold range in yield characteristics. Similar ranges in transgenic yield characteristics occurred in the 1R (7.6-fold difference in TCH and 7.2-fold difference in TSH) and 2R crops (12-fold difference in TCH and 12-fold difference in TSH). Agronomic performance of the transgenic materials ranged from near crop failure to double the yield of the commercial checks. Variance component estimates (Table 1) revealed that variance attributable to genotype was ≥ error variance for stalk weight, TCH, TSH, and EI in PC. The percentage of variation attributable to genotype effects was generally lower in 1R and 2R crops than PC for these yield traits. However, the ratio of KST variance attributable to genotype was notably low across crops, indicating that transformation procedures had a greater effect on sugarcane plant biomass than sucrose accumulation.

Experiment 2
Experiment 2 was conducted using the 30 VR 18 accessions selected in Exp. 1. Sixteen of the 30 accessions had higher EIs than CP 84-1198 in PC (Table 2), and 14 of 30 had higher EI in 1R (Table 3). Of these, six were selected for planting in increase plots based on PC data: VR 18-8, VR 18-9, VR 18-10, VR 18-54, VR 18-69, and VR 18-73. None of these accessions exhibited SCMV symptoms in the field. Regarding the rationale for selection of the higher-ranked clones, VR 18-54 and VR 18-9 had the highest EI in the PC crop. VR 18-33 was not selected for increase due to the presence of leaf scald [Xanthomonas albileans (Ashby) Dowson] disease and poor agronomic performance in the ratoon crop of Exp. 1 (data not shown). VR 18-69 and VR 18-10 were chosen due to high EIs in both the PC and 1R crops. VR 18-57 and VR 18-93 were not selected due to SCMV symptoms in the field. Finally, VR 18-8 was chosen over similarly ranked clones due to excellent ratoon performance in Exp. 1.


View this table:
[in this window]
[in a new window]
  		Table 2. Plant cane yield components and Sugarcane mosaic virus (SCMV) disease incidence for 30 virus-resistant (VR)-18 accessions in Exp. 2.

 

View this table:
[in this window]
[in a new window]
  		Table 3. First ratoon yield components and Sugarcane mosaic virus (SCMV) disease incidence for 30 virus-resistant (VR)-18 accessions in Exp. 2.

 
Genetic variation in the transgenic population decreased with increased selection pressure from Exp. 1 to Exp. 2, with TCH ranging from 70 to 149 t ha–1 in PC and 74 to 138 t ha–1 in 1R, and TSH ranging from 8.5 to 19.0 t sucrose ha–1 in PC, and 10.0 to 19.2 TSH in 1R. The extent of phenotypic variation decreased from a sevenfold range in Exp. 1 to a twofold range in Exp. 2.

On the basis of a combined five crop-years of data from the field, two VR 18 accessions (VR 18-8 and VR 18-54) were planted in 0.25-ha multiplication plots in 2004. In addition, 37 accessions from all four VR lines are being used in breeding efforts to combine resistance to SCMV strain E in this material with SCMV strain H resistance from other sources.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
CONCLUSIONS
 REFERENCES
 
Both agronomic performance and disease resistance data strongly indicate the superiority of transgenic plants generated from CP 84-1198 compared with CP 80-1827 callus tissue. Reasons for the superiority of CP 84-1198 transgenic accessions may include both higher yield potential and disease resistance in the starting parent material, as well as a greater tolerance of the cultivar to genetic transformation. Cultivar release data reveal that CP 84-1198 had higher KST (relative to the CP 70-1133 control) than CP 80-1827; however, sucrose yields of CP 80-1827 were higher than those of CP 84-1198 (Glaz et al., 1990, 1994). Both cultivars exhibited resistance to SCMV when released, but CP 80-1827 was more susceptible to SCMV (22–56% infected plots) than CP 84-1198 (0–11% infected plots) in this study (Table 1). Differential response of sugarcane cultivars to tissue culture has also been noted by Lourens and Martin (1987) and Hoy et al. (2003). Under our conditions, CP 84-1198 developed callus and regenerated more quickly than CP 80-1827 (data not shown). Such a tissue culture response may have resulted in less opportunity for somaclonal variation because of the shorter time spent in culture. Our results indicate that the effects of genetic transformation in sugarcane differed substantially for these two cultivars.

Transgenic barley plants were improved by cross-breeding to transfer the transgene to more suitable genotypes (Horvath et al., 2001). Additionally, Butterfield et al. (2002) showed that transgenic sugarcane plants that displayed stable inheritance of their transgenes could be used successfully as parents in a breeding program. However, due to potential meiotic instability of SCMV resistance conditioned by posttranscriptional gene silencing, it would be prudent to screen adult plants for resistance, as seedling phenotypes were unreliable. A similar strategy may be necessary for transgenic materials from genotypes such as CP 80-1827.

Significant differences in performance among VR lines cannot be entirely explained by transgenic parent, as the two superior lines (VR 14 and VR 18) originated from different cultivars. Differences in performance may have been due in part to differences in the explants used for transformation. VR 1 accessions, which had the lowest average yield in all three crops, were regenerated from young leaf roll callus, whereas the other lines were regenerated from inflorescence-derived callus. Hoy et al. (2003) found that tissue culture-derived CP 70-321 plants from apical meristem explants had significantly greater stalk weight and stalk diameter than those from leaf roll explants. Additionally, differences most likely were also due in part to effects created by the random integration of the transgenes into the sugarcane genome. Presently, we cannot control such position effects in our sugarcane transformation process.

Transgenic procedures necessarily involve cell culture in the undifferentiated state, which introduces the genetic variability termed somaclonal variation (Arencibia et al., 1999). Somaclonal variation in transgenic sugarcane has been documented during incorporation of insect resistance (Arencibia et al., 1999) and herbicide resistance (Leibbrandt and Snyman, 2003), and has been used to identify accessions with desirable traits (Liu, 1990; Leal et al., 1996). A large transgenic population (n = 100) was evaluated in this study. The larger the transgenic population evaluated, the greater the likelihood of discovering accessions with both desirable phenotype and successful transgene incorporation. However, large phenotypic variation in a large transgenic population will necessitate thorough field evaluation. Traditional sugarcane breeding programs require evaluation of thousands of crosses and 8 to 10 yr of field testing to produce a commercial cultivar. It was hoped that transgenic approaches would reduce this lengthy procedure; however, our experience indicates that evaluation of large populations and multiyear field testing is necessary in both sugarcane breeding strategies.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
REFERENCES
 
Transgenic sugarcane clones derived from CP 84-1198 parents were clearly superior to those derived from CP 80-1827, indicating differential cultivar response to genetic transformation. CP 84-1198 produced a greater number of recoverable explants than CP 80-1827, and these explants exhibited improved agronomic performance. Phenotypic variation in the population of 100 transgenic plants was extremely high, emphasizing the need for thorough field evaluation of transgenic sugarcane. However, the large variability in transgenic materials allowed for the identification of several transgenic accessions with improved agronomic performance and SCMV resistance compared with the commercial controls. Evaluation of large populations of transgenic sugarcane will combine benefits of increased probability of selecting superior material with the need for thorough field screening.


   ACKNOWLEDGMENTS
 
The authors gratefully acknowledge the assistance of Mr. Lee Liang and Mr. Ronald Gosa in data collection and processing. This research was supported by the Florida Agricultural Experiment Station and a grant from the Florida Sugar Cane League and approved for publication as Journal Series No. R-10674.

Received for publication December 30, 2004.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSIONS
 REFERENCES
 





This Article
Right arrow Abstract Freely available
Right arrow Figures Only
Right arrow Full Text (PDF) Free
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via ISI Web of Science (3)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Gilbert, R. A.
Right arrow Articles by Abouzid, A.
Right arrow Search for Related Content
PubMed
Right arrow Articles by Gilbert, R. A.
Right arrow Articles by Abouzid, A.
Agricola
Right arrow Articles by Gilbert, R. A.
Right arrow Articles by Abouzid, A.
Related Collections
Right arrow Crop Genetics
Right arrow Sugarcane

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
The SCI Journals Agronomy Journal Vadose Zone Journal
Journal of Natural Resources
and Life Sciences Education		 Soil Science Society of America Journal
Journal of Plant Registrations Journal of
Environmental Quality		 The Plant Genome