Assessing compensation for insect damage in mixed plantings of resistant and susceptible potatoes

Plant mixtures have been proposed for pesticidal transgenic potatoes as a means to reduce selection intensity favoring resistant insect genotypes. Colorado potato beetle,Leptinotarsa decemlineata (Say), defoliation was simulated in mixed plantings of susceptible and resistant potato “mimics” to evaluate yield compensation. Various mixtures of susceptible and resistant potato were planted at two densities and two locations in eastern North Carolina. Resistant plants were undamaged throughout the season whereas susceptible plants were completely defoliated by hand either during early or late bloom. The ability of non-defoliated plants to compensate for neighboring defoliated plants was investigated through single-plant and smallplot field experiments for 2 years. Yield compensation for defoliated plants by neighboring non-defoliated plants was not evident in our studies. Yield of two potato plants, positioned on either side of a defoliated plant, was not different from yield of two potato plants positioned on either side of a non-defoliated potato plant. Compensation in mixtures of resistant and susceptible potato was not evident using several non-linear regression analyses. A negative linear relationship existed between yield and an increasing percent of susceptible plants in the mixture for all planting densities, at each location, every year.