Publications /  Annual Report 1998

CIP scientists use the latest tools of modern biotechnology so that their research results can be applied to address food availability and increase the welfare of the poor.

Andean cultivated germplasm is analyzed by AFLP fingerprinting separated on an automated DNA sequencer, thanks to U.S. collaborators. The technology will soon be set up in-house to streamline access to the vast germplasm collections of CIP.

Recognizing the potential for increasing food production and improving food quality, CIP has continued to increase its investment in biotechnological research. Combining the most advanced biotechnological tools with the wealth of CIP’s extensive potato and sweetpotato germplasm collection, agricultural researchers are identifying specific sources of disease and pest resistance, determining the genes associated with these traits, and incorporating them into new breeding lines and varieties. This, in turn, helps protect the environment by reducing the need for insecticides and other agrochemicals.

Modern biotechnology comprises molecular and cell techniques for a range of scientific activities, including evaluating biodiversity, isolating and identifying specific genes associated with plant characteristics, and improving the efficiency of plant breeding. These methods can be used to genetically transform a crop by introducing the genes directly into cultivars. The cultivars retain their original desirable characteristics while gaining new ones through gene transfer.

Since potato was the first food crop to be genetically transformed, or "engineered," CIP scientists had a head-start in the application of biotechnological methods. Genetic engineering was introduced to CIP in 1985. Soon after, CIP was among the first to apply these techniques to sweetpotato. Since then, CIP has systematically produced new potato and sweetpotato clones by genetic engineering, and continues to test them in various ways, including in the field.

Breeding with Molecular Insight
Genetic maps for potato now exist for several species, including wild potatoes, primitive cultivated potatoes from the Andes, and modern cultivated potatoes. CIP is also developing maps for sweetpotato, a challenging task considering the genetic complexity and paucity of genetic information available for this crop.

Once compiled, the genetic knowledge is used to develop CIP’s research strategies. When the source of a particular desired trait has been identified, the gene or genes can be cloned and directly transferred, or incorporated indirectly into susceptible varieties using associated markers. Biotechnology is thus providing CIP with the tools to produce varieties with high levels of durable field resistance to pests and diseases, which means a reduction in the use of toxic chemicals.

By genetically mapping the gene loci in a range of diploid species, CIP researchers are compiling molecular data on sources of resistance in the Center’s potato germplasm collection, including resistance to late blight. The focus is on identifying polygenic, quantitative, or "horizontal" resistance, which is likely to be more durable than race-specific resistance when confronted by new, aggressive pathogens. Efforts to map quantitative resistance have recently been stepped up, and in doing so, CIP’s germplasm collection has paid multiple dividends.

CIP has carried out recurrent selection of populations of Solanum tuberosum ssp. andigena, a cultivated tetraploid potato indigenous to South America. Efforts are focused on improving resistance to late blight, complementing the currently available resistance in S. tuberosum ssp. tuberosum. A high level of resistance has also been found in S. phureja, a cultivated diploid potato. Both of these species are being used to genetically localize the genes that can confer quantitative late blight resistance.

Using random amplified polymorphic DNAs (RAPDs), amplified fragment length polymorphisms (AFLPs), and microsatellite markers, scientists have been able to identify several quantitative trait loci (QTL) that can contribute to the resistance. The next steps will be to identify QTLs from a diverse range of germplasm from the potato genepool, and to use them in molecular breeding.

But the search for applications of innovative biotechnological tools does not stop there. Researchers at the International Rice Research Institute (IRRI) and at Kansas State University are collaborating with CIP to develop a set of genes thought to play a broad role in plant defense. These genes can be used as probes for QTL mapping in other crops. If effective against late blight, they can be isolated, compared to existing cloned genes, and transferred to susceptible potatoes.

Breeding with Gene Technology
The introduction of genes through molecular breeding also benefits from the natural transfer of DNA through a bacterium, Agrobacterium tumefaciens. This is a plant pathogen that, in nature, transfers bacterial DNA into plant cells to produce tumors. Genetic engineers have been able to modify the bacterium to eliminate the tumor-inducing process so that only the desired gene(s) are transferred into the plant chromosomes. Chromosome segments from appropriate, large-insert-DNA libraries can also be used to modify the genetic composition of potato and sweetpotato.

One of the most promising applications of breeding with gene technology is the Bt potato. A gene from Bacillus thuringiensis (Bt) that confers resistance to the potato tuber moth (provided by Plant Genetic Systems, Gent, Belgium) was successfully transferred to potato. As a result of this genetic modification, varieties from developing countries have been engineered for resistance to potato tuber moth and are now being tested.

Dramatic results are seen in transgenic potato varieties with the Bt gene for resistance to the potato tuber moth in both foliage and tubers. Untransformed potatoes (left side of photos) show extensive damage to both leaves and tubers. Transformed potatoes (right side of photos) show almost no visible signs of damage.

Potato tuber moth inflicts heavy damage on small farmers’ storage crops throughout the developing world. This pest can cause significant losses in the field, especially in subtropical or warm temperate areas, and farmers apply heavy doses of insecticides to control it. Genetically engineered potato tuber moth resistance, achieved using the endogenous expression of a protein, has resulted in high levels of resistance in both tubers and Bt insecticidal foliage unsuitable for a wide range of agroecologies. clones and varieties

The Bt potato success has given scientists valuable experience that can be applied to sweetpotato. Currently, the most promising line of research to develop sweetpotato resistance to weevils is the use of exogenous genes, such as the Bt potato gene. The search is on for the most suitable Bt sweetpotato gene.