Transformation of potato (Solanum tuberosum) cultivars with a cry1Ac9 gene confers resistance to potato tuber moth (Phthorimaea operculella)

Eight potato (Solanum tuberosum) cultivars were transformed with a modified cry1 Ac9 gene under the transcriptional control of the CaMV 35S promoter using Agrobacteritan-mediated transformation with a nptII gene conferring kanamycin resistance as a selectable marker. Initially the transformation efficiency of two Agrobacterium strains (LBA4404 and AGLI) were compared using the potato cultivars 'Iwa' and 'Ilam Hardy'. Both strains resulted in similar numbers of regenerated shoots, but there was a higher proportion of off-types among plants transformed using the AGLI strain. Subsequently, the cultivars 'Karaka', 'Pacific', 'Red Rascal', 'Rua', 'Russet Burbank', and 'White Delight' were transformed with strain LBA4404. Putatively transformed lines with kanamycin resistance were assayed using multiplex polymerase chain reaction (PCR) with an endogenous potato actin as an internal control. From a total of 116 lines, 105 were confirmed as being PCR-positive for the nptII gene, of which 93 were also PCR-positive for the presence of the cry1 Ac9 gene. The amount of Cry protein in all transgenic lines tested was less than 60 ng/g fresh leaf tissue. The growth of potato tuber moth (Phthorimaea operculella) larvae was inhibited by foliage from greenhouse-grown plants of 77 of the transgenic lines (P < 0.05). Fifty-five of these resistant transgenic lines were described as having a phenotypic appearance comparable to the corresponding parental cultivars, when grown in the greenhouse. Southern analysis on four highly resistant lines revealed they contained two to five copies of the cry1 Ac9 gene. Several transgenic lines severely reduced larval growth while exhibiting a phenotype similar to their parent cultivar. These lines warrant further investigation in the field.