Enhanced Resistance to Control Potato Tuberworm by Combining Engineered Resistance, Avidin, and Natural Resistance Derived from, Solanum Chacoense

Potato tuberworm, Phthorimaea operculella (Zeller), is a destructive insect pest of potato, Solanum tuberosum (L.), found primarily in tropical and sub-tropical regions. It has recently become established in the northwestern United States. Avidin is a natural protein found in chicken (Gallus gallus L.) egg whites that has insecticidal properties against a number of lepidopteran and coleopteran pests. Biotin is a cofactor of carboxylases that are required for many important processes like lipogenesis, gluconeogensis, fatty acid and amino acid catabolism. Without biotin, an insect's growth is severely stunted, eventually leading to death. Avidin binds and sequesters biotin, limiting its availability during insect growth and development. Previous studies have demonstrated that avidin is effective against potato tuberworm. We sought to elevate resistance by combining avidin with natural host plant resistance factors from the wild species Solanum chacoense Bitter. We expressed avidin in two potato lines: MSE149-5Y, a susceptible potato line, and ND5873-15, a line with S. chacoense-derived resistance. The avidin expression was determined by ELISA to be 10.6 mu M in MSE75.7 (avidin) and 12.5 mu M in ND75.3 (avidin + S. chacoense-derived) in the tuber. Potato tuberworm bioassays were performed on MSE149-5Y, MSE75.7, ND5873-15, and ND75.3. Mortality was measured after 28 d. Mortality of larvae fed on MSE149-5Y (susceptible) did not differ significantly compared to the mortality of larvae fed on MSE75.7 (avidin) or ND5873-1 (S. chacoense-derived). Significantly higher mortality (98%) was observed for larvae fed on ND75.3 (avidin + S. chacoense-derived) tubers than for larvae fed on MSE149-5Y (susceptible). The present study is the first report of combining avidin with natural host plant resistance factors against potato tuberworm. Expressing avidin in combination with natural host plant resistance may be of value in managing potato tuberworm.