Potato tuberworm (Lepidoptera: Gelichiidae) resistance in potato lines with the Bacillus thuringiensis cry1Ac gene and natural resistance

Abstract

The potato tuberworm [Phthorimaea operculella (Zeller)] is one of the most destructive insect pests to potato (Solanum tuberosum L.) in tropical and subtropical regions, and it has recently become established in the Pacific Northwest of the United States. Combining natural resistance mechanisms with Bacillus thuringiensis (Bt) cry genes could be a potential solution to improve potato resistance to tuberworm. We have expressed Bt cry1Ac in two potato lines: Spunta, a susceptible potato line, and ND5873-15, a moderately resistant line with high foliar glycoalkaloids derived from Solanum chacoense. Putative transgenic lines of Spunta and ND5873-15 were developed using a vector construct pSPUD15 with the codon-modified Bt cry1Ac driven by the 35S CaMV promoter. Integration of Bt cry1Ac in Spunta and ND5873-15 transgenic lines was determined by PCR and Southern analysis. Protein expression in the transgenic lines (0-580 ng·g-1) was determined by ELISA. Plants expressing Bt cry1Ac were effective in controlling potato tuberworm first-instar larvae in the detached-leaf bioassays (up to 97% mortality) and in tuber bioassays (up to 99% mortality). Based on the assays conducted, the Bt cry1Ac Spunta lines were similar to the Bt cry1Ac ND5873-15 lines for potato tuberworm mortality. Constitutively expressed Bt cry1Ac would be a useful gene to use for host plant resistance to potato tuberworm.