able to produce long-chain fructans, but the sst lines are not. Field trials (ZG 6786-01-122 and 6786-01-136) conducted from 2000 to 2005 in Dahnsdorf (state of Brandenburg) by the BBA’s Institute of Integrated Plant Protection formed the experimental basis for the analysis performed from 2001 to 2003.
The extensive intervention into the carbohydrate metabolism of the potato variety Désirée caused by the tissue-unspecific integration of fructan synthesis was expected to have an effect on the health of the transgenic lines and could have additional implications for plant protection. The present study was therefore designed to evaluate and assess these effects, including crop development effects that might influence the competitive strength of potatoes against weeds. We therefore analyzed the morphology and phenology of the transgenic lines in comparison to that of the isogenic line (wild type). Susceptibility of the transgenic lines to the diseases potato wart (Synchytrium endobioticum) and late blight (Phytophthora infestans) and to the pests yellow cyst nematode (Globodera rostochiensis), root-knot nematode (Meloidogyne incognita) and Colorado potato beetle (Leptinotarsa decemlineata) was studied in a laboratory environment using field and/or greenhouse plant material. The effects of food quality on the Colorado potato beetle were investigated under both laboratory and field conditions (walk-in field cages). The fructose, glucose, saccharose and fructan content of leaf, root and tuber samples were determined by the Max Planck Institute in Golm for the tests of direct correlation between the susceptibility of the fructan-producing lines and their carbohydrate status.
Summary of main study findings:
1) Genetic intervention led to statistically significant and non-significant changes in certain traits of the transgenic lines compared to the isogenic cultivar (wild type).
Genetically based intra-construct differences were also observed for both constructs and lines. Correlation between these findings and the newly produced fructan or sugar content could not be established in all cases.
2) The seed tubers generated in the greenhouse remained genetically homogenous for three years. ISSR-PCR studies showed genetic differences between all transgenic lines and the isogenic line and differences between in-vitro propagated and commercially available isogenic cultivars. It is thus probable that the isogenic line propagated in the greenhouse is not derived from the same genetic pool as the transgenic lines or that a spontaneous mutation (somaclonal variation) of the isogenic cultivar occurred before testing.
3) Compared to the wild variety, all three SST/FFT lines showed delays in crop emergence, bud development and flowering. The main sprout length was shorter and the entire crop cover was missing during the entire vegetation period. Effects of seed tuber size on main sprout length could be excluded. The number of single flowers at first-order inflorescence was reduced. Depending on the line, the hairs on the lower side of the leaves were more or less dense than those of the isogenic cultivar. The number of sprouts and side sprouts per main sprout remained constant, but this data is not validated because the observed changes could not be confirmed over all years. The genetic modifications had no effect on yield, tuber size or starch morphology.
Depending on the year, the starch content of the SST/FFT lines was 2 to 3 percent lower than that of the wild variety. This relative decrease correlates with the fructan content and shows that fructan biosynthesis occurs at the expense of starch biosynthesis. The above-mentioned changes in phenology and morphology were observed in all three SST/FFT lines. These changes are presumably due to direct effects of SST line insertion or second transformation (integration of the FFT construct).
4) The three SST lines exhibited variable delays in bud and flower development, reductions in the number of single flowers at first-order inflorescence, increases in leaf hair growth, and reductions in starch content (2-3 %) compared to the isogenic cultivar. Based on these line-specific changes, we presume that some phenological changes in the SST/FFT lines were caused by the SST construct.
5) The phenological and morphological changes in all six lines were within the scope of the conventional variety spectrum of the potatoes controlled by the German Federal Office of Plant Varieties (Bundessortenamt). From the viewpoint of plant protection, it might be prudent to adapt the herbicide strategy to give preference to ground herbicides due to the missing crop cover with the SST/FFT lines.
6) Based on our findings and those of our research partners, we could not determine whether the observed pleiotropic effects of the SST/FFT lines were caused by changes in the water supply or by shifts in the balance of a plant hormone (gibberellic acid). It seems probable that the complicated genetic interventions may have influenced various cascades of potato metabolism during the transformation process and that these interactions could have led to detectable or undetectable modifications in various traits.
7) Genetic modification did not alter leaf susceptibility to P. infestans in any of the SST or SST/FFT lines. However, tuber susceptibility decreased in the SST/FFT lines due to the presence of fructan, but remained unchanged in the SST lines. The negative correlation between tuberal fructan content and mycel growth was also confirmed in liquid cultures.
8) The reactions of the transgenic tubers with potato wart (S. endobioticum) pathotypes 1 and 18 were identical to those of the wild type. In addition, no differences between the transgenic and isogenic lines were observed in regard to the number of proliferations and weight.
9) The transgenic and isogenic lines showed identical reactions to the yellow cyst nematode (G. rostochiensis). Reproduction of the nematode also remained unchanged.
10) Reproduction of the root-knot nematode (M. incognita) was lower in the SST/FFT lines than in the isogenic line. This effect of genetic modification is presumably due to altered root volume as a result of shortening of the main sprout or to the availability of fructan in the root.
11) The altered food quality in the SST and SST/FFT lines under greenhouse conditions did not have any long or short-term effects on larval development and eclosion or on female reproduction of the Colorado potato beetle (L. decemlineata).
12) The long-term feeding of L. decemlineata with transgenic plants in the lab decreased the genetic similarity (RAPD pattern) of all seven subpopulations by about 4 percent, but the strong homogeneity of the laboratory population established by decades of laboratory breeding was not affected.
13) Effects of food quality on larval weight and host preference for the reproduction of L.
decemlineata were only observed under field conditions. Depending on the stage of plant development, variable reductions in infestation appeared in the SST/FFT lines after both natural infestation and artificial output. This effect is most probably due to a change in morphology (growth, leaf hair) or in the type and concentration of plant chemicals (including volatile substances) in the SST/FFT lines compared to the isogenic cultivar and the SST lines. Nevertheless, synergistic effects are also possible.
14) Based on the observed differences in parameter values for selected traits of the Colorado potato beetle and in the carbohydrate content of greenhouse and field plants, we conclude that field cultivation is indispensable for achieving a robust risk assessment for the fructan potato. In addition, the feasibility of achieving long-term,
diapause-free laboratory populations of L. decemlineata for such biotests remains questionable.
None of the observed changes in the three SST/FFT lines regarding their phenotype, morphology and susceptibility to P. infestans, M. incognita, and L. decemlineata justify a new classification of the susceptibility reaction of the potato variety Désirée according to the criteria of the German Federal Office of Plant Varieties (Bundessortenamt). Since the susceptibility of all SST/FFT lines to pests and diseases was lower than that of the isogenic line, we do not expect that their cultivation would lead to an increased need for pesticides.
This is in compliance with guidelines for integrated plant protection and with the objectives of the German Ministry of Food, Agriculture and Consumer Protection’s Reduction Program for Chemical Plant Protection. From a plant health and plant protection perspective, the cultivation of the transgenic fructan potato does not raise any more agricultural or environmental issues than the cultivation of conventional potato varieties.
The disease monitoring procedure for conventional potatoes, which has been in place for many years, is thus sufficient to fulfil the monitoring requirements for cultivation of the transgenic potatoes.