Number 10                                                  

 

The comparison of transgenic and non-transgenic sugarbeet cultivars in 2000

                                                                  

                                                           Stephen Kaffka[1], Gary Peterson[2]

 

Introduction

 

Apart from basic research, the transformation of sugarbeets using molecular biology techniques takes place almost exclusively in Europe, as part of the plant breeding programs of several large, private sugarbeet seed firms.  The starting point for most transformation and  subsequent cultivar development usually are elite sugarbeet breeding lines which grow best in Europe (Kaffka and Lemaux, 1996).  Currently, two companies sell seed in California:  Spreckels/Holly Hybrids and Betaseed.  Neither has entered transgenic varieties in coded trials around the state at this point in time.  There is no molecular breeding work being carried out on sugarbeet in California, and this may delay the availability of adapted transgenic cultivars.   The recent and widespread success in California of European breeding lines like Betaseed’s 4776R, however, suggest that more rapid availability of transformed lines in California may be possible than previously thought (Kaffka and Lemaux, 1996).  Because of this success, when advanced, transformed breeding lines become available from European breeding programs for testing in California, their performance should be evaluated promptly.  Also, despite record high yields in California based on the use of newer commercial cultivars, concern remains that some lines may not have sufficient tolerance of unique or especially harmful diseases in California like curly top or virus yellows, or that they have limited bolting resistance, justifying caution in using them in overwintered areas.  


Betaseed has developed transformed herbicide tolerant sugarbeet lines related to cultivars currently approved for sale in California.  Tolerance is to glufosinate ammonium (G-A), a broad spectrum contact herbicide marketed as Liberty®.  G-A is widely used by Betaseed as a marker gene in its transformation programs.  Liberty® is now registered in California.  This year, Betaseed  has also developed a glyphosate (Roundup®) resistant line as well.   To evaluate the performance of  herbicide tolerant sugarbeet cultivars at the request of Betaseed, Inc., the yield of transgenic sugarbeets was compared to a commercially available Betaseed cultivar in a trial carried out at the agronomy farm at UC Davis.  The objectives of this trial were:

1.  to compare the yield of transgenic and non-transgenic sugarbeets, and

2.  to compare the growth of the herbicide tolerant lines with and without the herbicides to which they are tolerant. 

 

Methods

 

Betaseed cultivar 4776R, and two elites line modified to be tolerant to the herbicides glufosinate ammonium or glyphosate were grown under field conditions on the UC Davis agronomy farm during the spring-fall period in 2000.  Plots were four rows wide (30 inches per row) and thirty five feet long.  These four rows were treated with the different herbicides used and the middle two rows were harvested for yield and quality determinations.  Treatment combinations are listed in Table 1.  One of the entries (glyphosate tolerant) had poor seedling emergence.  At harvest, gaps in the row greater than 18 inches were measured, and plot yield adjusted for missing plants.  Different herbicide treatments were applied to the transgenic cultivars to determine whether there would be any yield loss due to the use of G-A or glyphosate on tolerant plants.   Planting occurred on May 31  and the plots were irrigated on June1.   Plots were harvested on October 3.  In accordance with the USDA/APHIS protocol, all transgenic beets were destroyed after harvest.  Powdery mildew was controlled from the time it was observed in the plots using Thiolux, a wetable sulfur.  There were three applications made starting in early August   Roots were analyzed for sugar content and soluble solids at the USDA’s Salinas laboratory.

 

Results

 

All results are reported in Table 2.  Treatment contrasts are reported in Table 3.

 

Root yields.  Root yields averaged 19.83 tons per acre overall.   Comparisons are presented in two ways.   The transgenic cultivar resulted in identical or slightly higher root yields for the most part (Table 2)  but differences were small and insignificant (Tables 2 and 3).

Sugar percent.  Sugar percent was not significantly different among the cultivars and treatments (Tables 2 and 3).  Sugar percent was lower than in the previous tow years trial, but  was similar to the sugar percent of many beet crops in the northern California area this fall (John Watson-Spreckels Sugar, personal communication).

 

Sugar yield.  Gross sugar yields were similar among all treatments (Tables  2 and 3).

 

Discussion

 

The transgenic LL cultivar showed a marked susceptibility to powdery mildew in this year’s trial.  A similar tendency was observed in 1999, but not in 1998 (Kaffka and Peterson, 1999; Kaffka et al., 1998).  Mildew was controlled using sulphur.   Despite the mildew, cultivar performance was not affected and sugar yields were similar to grower’s results in the region.  Because of some large plot areas with missing plants, the RR cultivar’s yields may have been overestimated by the plot adjustment method used.  The roots in these plots tended to be larger than in other plots due to lessened competition among the remaining plants.  We believe that the slightly higher root yields for this cultivar are an artifact.  Both yields and sugar content were lower than in the previous two years of the trial (Kaffka et al., 1998; Kaffka and Peterson, 1999).  Plots were planted later this year, and sugar content in fall harvested beets throughout the central valley was lower than in previous years.  The average sugar percent for Yolo county, where this trial took place, was 13.53 %, almost identical to the trial average.

There are some potential advantages for the use of herbicide tolerant sugarbeets in California.  Weed control would be simplified, and possibly made less expensive.  A broad spectrum material like Roundup® would control most of the weeds in sugarbeet fields, whereas currently several different herbicides are required.  Some of these have been or are being reviewed under the Food Quality Protection Act for removal.  Compared to these, both Roundup® and Liberty® are considered less toxic, and presumably less harmful to the environment.

Disadvantages would include higher seed costs, at least initially, and the potential for escape of herbicide tolerance genes.  This could occur if sugarbeets flower and set seed, as happens commonly in overwintered sugarbeet crops, or if out-crossing with weedy relatives tkaes place.  Out-crossing might occur in the Imperial Valley where Beta macrocarpa, a near relative of sugarbeet, infests fields.  The consequence of escape would be self-sown sugarbeet or weed seedlings that are resistant to Roundup® or Liberty®.  Resistance to sugarbeet herbicides characterizes both wild beets, from bolted crops in previous years, and Beta macrocarpa seedlings, so escape would not materially change sugarbeet weed management.  Both transgenic weed beets and weedy relatives would still be controlled by the herbicides used for other crops in the rotation to which beets are susceptible at present.

 

References

 

Kaffka, S.R. and Lemaux, P.G. (1996).  The use of molecular breeding methods to advance the sugarbeet industry in California.  DANR Spec. Pub. May, 1996. 48p  

 

Kaffka, S.R., Peterson, G., and Daxue, D., (1998).  The comparison of transgenic and non-transgenic sugar cultivars.  Sugarbeet Notes, December, 1998.  Dept. of Agronomy and Range Science, University of Calif., Davis, California.

 

Kaffka, S.R., and Peterson, G. (1999).  The comparison of transgenic and non-transgenic sugar cultivars in 1999.  Sugarbeet Notes, December, 1999, no. 7.  Dept. of Agronomy and Range Science, University of Calif., Davis, California.

 

Table 1. Treatments

 

Cultivar

 

Herbicide treatments

 

4776R

 

(06/25/2000):  Progress®  applied @ 0.3 lb ai per acre

 

RR(+)

 

(06/25/2000): Roundup @ 1.0 lb a.i. per acre

 

RR (-)

 

(06/25/2000):  Progress®  applied @ 0.3 lb ai per acre

 

LL(+)

 

(06/25/2000): Liberty®  applied  @ 28 oz. per acre as formulated (no adjuvant)

 

LL (-)

 

(06/25/2000):  Progress®  applied @ 0.3 lb ai per acre

Treatments:  4776R (commercial cultivar-control); RR: Roundup® tolerant; LL: Liberty® tolerant. There were six replications of each treatment.  Sulfur was applied three times starting in early August.

 

 

 

 

 

 

 

Table 2.  Results

 

Treatment

 

Root yield

(t/ac)

 

Sugar %

 

Sugar yield

(lbs/ac)

 

4776R

 

19.8

 

13.58

 

5380

 

RR(+)

 

20.8

 

13.51

 

5600

 

RR(-)

 

20.3

 

13.83

 

5530

 

LL (+)

 

20.0

 

13.70

 

5460

 

LL(-)

 

18.6

 

13.63

 

5060

 

LSD(0.05)

 

2.23

 

0.76

 

580

Table 3.  Treatment contrasts

 

Variable

 

Contrast

 

MS

 

F

 

p=

 

Root yield

 

LL (+) vs LL(-)

 

5.741

 

1.68

 

0.2098

 

 

 

RR (+) vs. RR(-)

 

1.541

 

0.45

 

0.5097

 

 

 

LL(+) vs. 4776R

 

0.0533

 

0.02

 

0.9019

 

 

 

RR(+) vs. 4776R

 

1.841

 

0.54

 

0.4716

 

 

 

LL vs RR

 

7.4817

 

2.19

 

0.1547

 

Sugar %

 

LL (+) vs LL(-)

 

0.01333

 

0.03

 

0.8558

 

 

 

RR (+) vs. RR(-)

 

0.3008

 

0.77

 

0.3921

 

 

 

LL(+) vs. 4776R

 

0.0408

 

0.10

 

0.7506

 

 

 

RR(+) vs. 4776R

 

0.1008

 

0.26

 

0.6181

 

 

 

LL vs RR

 

0.00042

 

0.00

 

0.9744

 

Gross sugar yield

 

LL (+) vs LL(-)

 

0.1141

 

1.98

 

0.1748

 

 

 

RR (+) vs. RR(-)

 

0.00403

 

0.07

 

0.7941

 

 

 

LL(+) vs. 4776R

 

.000403

 

0.07

 

0.7941

 

 

 

RR(+) vs. 4776R

 

0.0161

 

0.28

 

0.6026

 

 

 

LL vs RR

 

0.1396

 

2.42

 

0.1354

 


[1]Extension agronomist, Department of Agronomy and Range Science, University of California, Davis, California 95616-8515; srkaffka@ucdavis.edu

[2]Staff Research Associate, Department of Agronomy and Range Science