Evaluation of field grown potato lines transgenic for a <i>cry</i>1Ac9 gene conferring resistance to potato tuber moth

Abstract

Phthorimaea operculella (Zeller), potato tuber moth (PTM), is an important pest of potatoes. The larvae of this insect are difficult to control with insecticides because they mine into foliage and tubers. Seven potato cultivars were genetically engineered with a Bacillus thuringiensis cry1Ac9 gene to confer resistance to PTM larvae. Fifty-six transgenic lines were established in the field at Lincoln, Canterbury, as small plots of 10 plants along with replicate control plots of the same, but non-transgenic, cultivars. Fortyfour of the transgenic lines were phenotypically normal. Foliage excised from these plants was challenged with PTM larvae in the laboratory. All but one line inhibited larval growth compared to non-transgenic plants (P<0.05). For transgenic plants the growth indices of larvae fed field-grown foliage were similar to those fed greenhouse-grown foliage. Thirteen of the 43 resistant lines inhibited larval growth by ≥40% and produced tuber yields comparable to the non-transgenic plants.

Regeneration of multiple shoots from transgenic potato events facilitates the recovery of phenotypically normal lines: assessing a cry9Aa2 gene conferring insect resistance

“…Larvae recovered from these lines after the 9-day bioassay were small and of substantially lower weight. In our previous studies, PTM larvae with such poor growth in response to cry gene expression in transgenic potatoes have failed to reach pupation, resulting in complete disruption to the life cycle [ 14 , 16 , 28 ].…”

“…The usual approach for producing transgenic cultivars in clonal crops involves the development of a large number of independently derived transgenic lines in order to recover several lines with the desired phenotype and transgene expression [ 2 , 3 ]. When developing large populations of independently derived transgenic lines, only the first shoot to regenerate from each transformation event is usually selected [ 14 , 17 ]. This is based on a widely held view that minimum time in tissue culture is favourable to avoid undesired somaclonal variation [ 32 ], and the assumption that a shoot taking a longer time to regenerate has a greater chance of producing off-types.…”

“…Leaf material from all transgenic lines with phenotypically normal shoots when grown in the greenhouse for at least 8 weeks was used for the PTM larvae bioassays. The insects used in the bioassays were obtained from a laboratory colony maintained as previously described [ 14 ]. The bottom of a 350 ml plastic container was lined with dry filter paper (Whatman ® , No.…”

“…Genotype, explant origin, cultivation period and the culture conditions are reported as four critical variables contributing to somaclonal variation [ 8 ]. The frequency of off-types attributed to somaclonal variation among populations of transgenic potatoes has been recorded as 15-80%, depending on the potato cultivar [ 9 - 15 ].…”