Peroxidase and polyphenol oxidase activity in cassava genotypes infested with Phenacoccus manihoti

Abstract

The cassava mealybug, Phenacoccus manihoti (Matile-Ferrero) (Hemiptera: Pseudococcidae), has become an important pest with major potential to damage cassava, Manihot esculenta Crantz (Euphorbiaceae), around the world. To find new sources of plant resistance, the development of P. manihoti on 18 cassava genotypes was evaluated (duration of embryonic, nymphal, egg-adult, pre-oviposition, and oviposition periods, longevity, and fecundity), and the defense-related peroxidase (POD) and polyphenol oxidase (PPO) activities in the leaves were measured. The fecundity of P. manihoti was the parameter most affected by the cassava genotype that the insect was fed. POD activity was negatively correlated with the intrinsic rate of increase (r m ) of P. manihoti. PPO activity was negatively correlated with insect fecundity, net reproductive rate (R 0 ), and r m and positively correlated with population doubling time. According to hierarchical groupings of the genotypes tested, three genotypes were resistant to P. manihoti, five were moderately resistant, nine were susceptible, and one was highly susceptible. This information could aid future genetic breeding programs, leading to development of more resistant commercial cassava varieties which could be used in integrated pest management systems.