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The Bt potatoes

The Bt potatoes

Through the support of the Belgian Agency for Development and Cooperation (BADC) in the early 1990s, Belgian technology was applied to engineer resistance to potato pests. Initially the work concentrated on transformation of developing-country potato varieties that were highly susceptible to the potato tuber moth.

The pest problem

Potato tuber moth (PTM, Phthorimaea operculella) is the single most important insect pest on potatoes in developing countries. It causes damage primarily in storage, where losses can be devastating in the absence of adequate control measures. To a lesser extent, PTM also causes damage to potatoes in the field, especially in warm temperate and subtropical climates.

Even slightly damaged tubers lose nearly all their market value. To avoid such damage, farmers in some areas use massive applications of insecticides to control PTM populations. CIP researchers have developed integrated pest and disease management programs to reduce or eliminate the use of costly and potentially harmful pesticides in developing countries. Successful programs integrate many components, among them prophylactic and sanitary measures, clean planting materials, physical and chemical traps, and biological controls. But host plant resistance is by far the most important component of any integrated pest and disease management strategy.

In developing countries, pest resistant varieties do not exist because classical breeding approaches have been unable to build sufficient PTM resistance into potatoes. Biotechnology, on the other hand, has proven successful in genetically engineering PTM resistance in potatoes—based on the endogenous expression of Bacillus thuringiensis (Bt) toxins.

The Bt gene

The genes determining the expression of the toxin were originally isolated from specific strains of B. thuringiensis (Bt) and have been improved for high levels of gene expression in plants at the Belgian company PGS in Gent.

Gene construct bearing the Bt gene that confers insect resistance and a plant selectable marker (KmR) flanked by the borders (RB and LB) of the transferred DNA.

Bt varieties

Several developing-country potato varieties have been transformed with the Bt gene to express resistance to the potato tuber moth.

  • in Central Africa (Rwanda, Burundi, Uganda, Congo) resistant varieties include Mabondo, Sangema, Murca, and Cruza 148;
  • for the Andean region (Peru, Bolivia, Ecuador), PTM resistance is now in Tomasa Condemayta, Costanera, Achirana INTA, María Tambeña, and Revolución;
  • in Colombia, Pardo Pastusa has been transformed;
  • Costa Rica now has resistant Atzimba, and;
  • for both North Africa (Egypt, Tunisia, Morocco) and the Southern cone of South America (Argentina, Chile), Desiree has been transformed with the Bt gene.

PTM distribution; S. tangolias (t), T. solanivora (¡), P. operculella (l) and target countries for Bt varieties.

Bt potatoes in the field

Potatoes with engineered resistance, planted for three consecutive years at different locations, under careful adherence to prevailing biosafety regulations, showed high levels of resistance to the potato tuber moth in all cases. No adverse effects on naturally occurring insects were observed in these environments.

In engineering Bt-mediated PTM resistance, as in any resistance breeding effort, it is essential to take into account the possibility that the target pest populations will develop resistance to the toxin used. Such resistance to Bt toxins has already been found in controlled laboratory conditions and under field conditions for specific pests. More applied research is needed to develop management practices that can be recommended when varieties with Bt-mediated insect resistance are introduced in farmers’ fields.

Dramatic results are seen in transgenic potato varieties with the Bt gene for resistance to the potato tuber moth in both foliage and tubers. On the left, untransformed potatoes show extensive damage to both leaves and tubers. On the right, transformed potatoes show almost no visible signs of damage.

The Bt potatoes

Through the support of the Belgian Agency for Development and Cooperation (BADC) in the early 1990s, Belgian technology was applied to engineer resistance to potato pests. Initially the work concentrated on transformation of developing-country potato varieties that were highly susceptible to the potato tuber moth.

The pest problem

Potato tuber moth (PTM, Phthorimaea operculella) is the single most important insect pest on potatoes in developing countries. It causes damage primarily in storage, where losses can be devastating in the absence of adequate control measures. To a lesser extent, PTM also causes damage to potatoes in the field, especially in warm temperate and subtropical climates.

Even slightly damaged tubers lose nearly all their market value. To avoid such damage, farmers in some areas use massive applications of insecticides to control PTM populations. CIP researchers have developed integrated pest and disease management programs to reduce or eliminate the use of costly and potentially harmful pesticides in developing countries. Successful programs integrate many components, among them prophylactic and sanitary measures, clean planting materials, physical and chemical traps, and biological controls. But host plant resistance is by far the most important component of any integrated pest and disease management strategy.

In developing countries, pest resistant varieties do not exist because classical breeding approaches have been unable to build sufficient PTM resistance into potatoes. Biotechnology, on the other hand, has proven successful in genetically engineering PTM resistance in potatoes—based on the endogenous expression of Bacillus thuringiensis (Bt) toxins.

The Bt gene

The genes determining the expression of the toxin were originally isolated from specific strains of B. thuringiensis (Bt) and have been improved for high levels of gene expression in plants at the Belgian company

PGS in Gent.

Gene construct bearing the Bt gene that confers insect resistance and a plant selectable marker (KmR) flanked by the borders (RB and LB) of the transferred DNA.

Bt varieties

Several developing-country potato varieties have been transformed with the Bt gene to express resistance to the potato tuber moth.

  • in Central Africa (Rwanda, Burundi, Uganda, Congo) resistant varieties include Mabondo, Sangema, Murca, and Cruza 148;
  • for the Andean region (Peru, Bolivia, Ecuador), PTM resistance is now in Tomasa Condemayta, Costanera, Achirana INTA, María Tambeña, and Revolución;
  • in Colombia, Pardo Pastusa has been transformed;
  • Costa Rica now has resistant Atzimba, and;
  • for both North Africa (Egypt, Tunisia, Morocco) and the Southern cone of South America (Argentina, Chile), Desiree has been transformed with the Bt gene.

PTM distribution; S. tangolias (t), T. solanivora (¡), P. operculella (l) and target countries for Bt varieties.

Bt potatoes in the field

Potatoes with engineered resistance, planted for three consecutive years at different locations, under careful adherence to prevailing biosafety regulations, showed high levels of resistance to the potato tuber moth in all cases. No adverse effects on naturally occurring insects were observed in these environments.

In engineering Bt-mediated PTM resistance, as in any resistance breeding effort, it is essential to take into account the possibility that the target pest populations will develop resistance to the toxin used. Such resistance to Bt toxins has already been found in controlled laboratory conditions and under field conditions for specific pests. More applied research is needed to develop management practices that can be recommended when varieties with Bt-mediated insect resistance are introduced in farmers’ fields.

Dramatic results are seen in transgenic potato varieties with the Bt gene for resistance to the potato tuber moth in both foliage and tubers. On the left, untransformed potatoes show extensive damage to both leaves and tubers. On the right, transformed potatoes show almost no visible signs of damage.

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