Insect-resistant potato: NewLeafTM

NatureMark^® potato lines named NewLeaf^TM confer resistance to Colorado potato beetle (CPB; Leptinotarsa decemlineata Say). Colorado beetle is a primary pest of North America and elsewhere, larvae emerging from egg masses about one week after deposition then feeding on foliage. Mature larvae leave the plant and pupate in soil to emerge as adults one week later and begin feeding on foliage yet again. NewLeaf^TM potatoes were commercialized in the USA and Canada after more than ten years of development work in laboratories, glasshouses and fields across North America. The potatoes were transformed with a gene, which encodes for the Cry3A protein from the bacterium Bacillusthuringiensis (var. tenebrionis) using the constitutive 35S CaMV promoter. The Cry 3A protein is part of a family of proteins used for more than 30 years by organic producers, home gardeners, etc. The product has been endorsed by the World Health Organisation (WHO) and other regulatory agencies throughout the world. The protein affects directly only the target pest, Colorado potato beetle (CPB) and has no effect on other insects, mammals or wildlife. Growers have reduced insecticide usage on average by 42%. NewLeaf^TM was approved in the USA in May 1995. The relevant agencies in the USA, the Food and Drug Administration, (FDA), United States Department of Agriculture (USDA) and Environmental Protection Agency (EPA) have approved the product based on substantial equivalence to other Russet Burbank potatoes. The product has also been approved by Health Canada, Agri-Food Canada and Agriculture Canada. Japan and Mexico have also approved the use of NewLeaf^TM potato.

The first generation of NewLeaf^TM potatoes included cultivars Atlantic, Superior and Russet Burbank and all of these NewLeaf^TM varieties have been completely de-regulated by the FDA, USDA and EPA in the USA. Commercial adoption rates between1995 and 1999 are shown in Table 9.3. A range of transgenic lines were selected with superior agronomic characteristics in addition to CPB resistance. Cultural management guidelines were also developed for growers. Out of the programme arose NewLeaf^TM 6 Russet Burbank which is high yielding (earlier tuber bulking) and which produces a high percentage of quality grade potatoes classified as US and Canadian number ones. This has required optimisation of row spacings and development of appropriate fertiliser regimes. NewLeaf^TM 6 also has extended dormancy and shows improved long storage characteristics. Since the potato is completely protected from CPB it appears to need no additional protection from this pest. Plants modified to express insecticidal proteins from Bacillus thuringiensis (referred to as Bt-protected plants) are believed to provide a safe and highly effective method of insect control. Bt-protected corn, cotton, and potato were introduced into the United States in 1995/1996 and grown on a total of approximately ten million acres in 1997, 20 million acres in 1998, and 29 million acres globally in 1999. These crops provide highly effective control of major insect pests such as the European corn borer, south-western corn borer, tobacco budworm, cotton bollworm and pink bollworm, in addition to CPB. They reduce reliance on conventional chemical pesticides and appear to provide notably higher yields in cotton and corn. The estimated total net savings to the grower using Bt-protected cotton in the United States was approximately $92 million in 1998. Other benefits of these crops include reduced levels of the fungal toxin fumonisin in corn and the opportunity for supplemental pest control by beneficial insects due to the reduced use of broad-spectrum insecticides. Insect resistance management plans are being implemented to prolong the effectiveness of these products.

	Table 9.3 NewLeafTM commercial adoption rate. Varieties: Russet Burbank, Atlantic and Superior
	1995		1,800 acres of commercial production. 54Mlbs of raw product used for tablestock and French fries.
	1996		10,000 acres of commercial production. 300Mlbs of raw product used for tablestock and French fries.
	1997		30,000 acres of commercial production. 900Mlbs of raw product used for tablestock and French fries.
	1998		48,000 acres of commercial production. 1.4B lbs of raw product used for tablestock and French fries.
	1999		55,000 acres of commercial production. 1.65B lbs of raw product used for tablestock and French fries.

Extensive testing of Bt-protected crops has been conducted which establishes the safety of these products to humans, animals, and the environment. Acute, sub-chronic, and chronic toxicology studies conducted over the past 40 years have established the safety of the microbial Bt-products, including their expressed insecticidal (Cry) proteins, which are fully approved for marketing. Mammalian toxicology and digestive fate studies, which have been conducted with the proteins produced in the currently approved Bt-protected plant products, have confirmed that these Cry proteins are non-toxic to humans and pose no significant concern for allergenicity. Food and feed derived from Bt-protected crops, which have been fully approved by regulatory agencies, have been shown to be substantially equivalent to the food and feed derived from conventional crops. Non-target organisms exposed to high levels of Cry protein are virtually unaffected, except for certain insects that are closely related to the target pests. Because the Cry protein is contained within the plant (in microgram quantities), the potential for exposure to farm workers and non-target organisms is extremely low. The Cry proteins produced in Bt-protected crops have been shown to degrade rapidly when crop residue is incorporated into the soil. Thus the environmental impact appears to be negligible. The human and environmental safety of Bt-protected crops is further supported by the long history of safe use for Bt microbial pesticides around the world.

For several decades the primary control strategy for CPB has been the use of chemical insecticides and about 22 active ingredients are registered, in Canada for example, for this purpose. However, restrictions in the modes of actions of insecticides coupled with repeated applications have led to resistance development in most commercial production regions in Canada (Stewart, 2000). The entry of new products with novel modes of action such Bt atosxin and products such as cyromazine and imidacloprid give more grower flexibility and reduce the potential for resistance development. Other insecticides are under development. Insecticide with Bt protein as the active ingredient is primarily effective against larvae only. Crop rotation is an important control strategy for growers too, as might be biological control using insect-destroying fungi such as Beauveria bassiana and beneficial nematodes such as Steinemema carpocapsae. However, the most spectacular development has been Bt with transgenics. Tests on Prince Edward Island and elsewhere in North America have shown that the technology is effective against both adults and larvae. Potato plant mixtures of 70% GM and 30% non-GM appear to be as effective in controlling CPB beetle numbers as GM monocultures. Indeed, border rows of transgenics can reduce the number of colonising beetles entering a field. CPB appeared in Europe in the 1920s and since 1980 has occurred in practically the entire European continent with the exception of the UK and Scandinavia. Quarantine actions are implemented only in the UK.

Recent work (Mohammed et al, 2000) has evaluated potato tuber moth resistance in tubers of transgenic potato lines expressing an alternative Bt protein encoded by the Bt-cry5 gene. The potato tuber moth is the most destructive pest of potato in tropical and sub-tropical countries. Larvae attack both foliage and tubers in the field and in storage. Moth mortality was 100% in transgenic lines of cultivar Spunta using the constitutive cauliflower mosaic virus promoter (35S CaMV).