Development and Evaluation of Potatoes Transgenic for a cry1Ac9 Gene Conferring Resistance to Potato Tuber Moth

Abstract

Transgenic potato (Solanum tuberosum L.) lines of two cultivars, Ilam Hardy and Iwa, were developed using Agrobacterium-mediated transformation to transfer a cry1Ac9 gene under the transcriptional control of the CaMV 35S promoter. PCR confirmed the presence of the nptII selectable marker gene in all recovered lines. All ten lines of Ilam Hardy and 14 of 15 Iwa lines were PCR-positive for the cry gene. In greenhouse trials, all Ilam Hardy transgenic lines produced phenotypically normal plants and significantly inhibited larval growth of potato tuber moth (Phthorimaea operculella Zeller). In contrast, only 60% of the Iwa transgenic lines produced phenotypically normal plants, but all lines positive for the cry gene significantly inhibited larval growth. All transgenic lines with a greenhouse appearance equivalent to the nontransgenic controls and improved resistance to potato tuber moth larvae were planted in the field. Three of the ten Ilam Hardy lines and two of the eight Iwa lines retained phenotypically normal appearance in the field and produced tuber yields equivalent to the nontransgenic controls. All five of these transgenic lines significantly inhibited larval growth of potato tuber moth on excised field-grown leaves. A high correlation was established between larval growth indices from the greenhouse and the field. A transgenic line from each cultivar inhibited larval growth by over 40%, and the line derived from Ilam Hardy prevented pupation of all larvae. Southern analysis on these five elite lines revealed that they contained either one or two copies of the cry1Ac9 gene. The amount of Cry protein in all transgenic lines tested was less than 60 ng·g-1 of fresh leaf tissue. A transgenic line from each cultivar was identified with comparable phenotypic appearance and yield to their parent cultivars coupled with high resistance to PTM.