Construction of a comprehensive evaluation model for constitutive resistance traits of tea cultivars to the pests Matsumurasca onukii and Dendrothrips minowai

As major pests in tea plantations, Matsumurasca onukii Matsuda (Hemiptera: Cicadellidae) and Dendrothrips minowai Priesner (Thysanoptera: Thripidae) reduce tea yields and cause large economic loss. Host plant resistance is one of the most effective and economical potential pest management strategies but is not well understood in tea. This study aimed to screen tea lines to determine chemical and structural traits that were associated with resistance to both herbivore species and then develop comprehensive resistance indicators and evaluation model of insect resistance. In addition, we modelled host plant identification and selection by the two pests and established resistance grading criteria for each. Traits positively associated with resistance to M. onukii were: concentrations of nonanal and dodecane, epidermal thickness of adaxial leaf surface, and ratio of this to leaf thickness. Negatively associated traits were: concentrations of malonic dialdehyde and linalool, ratio of adaxial leaf cuticle thickness to leaf thickness, and ratio of abaxial cuticle thickness to leaf thickness. For D. minowai , length of leaf, trichome density of buds, and caffeine content were positively associated with resistance; whilst dodecane and phenethyl alcohol concentrations as well as several color parameters of foliage were negatively associated. To comprehensively evaluate the insect resistance of tea cultivars, the affiliation function method was used and the results of the model showed significantly correlation for observed population densities of both pests. This study provides the first comprehensive framework for host plant resistance traits and will underpin risk assessment among existing cultivars and selection in future plant breeding programs.