Potential structural and biochemical mechanisms of compositae wild species resistance to Alternaria tenuissima

Disease assessment to measure severity of alternaria leaf spot (Alternaria tenuissima (Fr.) Wiltsh.) was performed in 32 wild species of Compositae family by seedling inoculation. It was found that two species were resistant, four were moderately resistant, and others were susceptible to various degrees. Some leaf morphological traits of two resistant and two highly susceptible wild species were studied. Trichome density and height and wax content were found to be associated with plant passive resistance, while stomata density was not associated. After A. tenuissima inoculation, enzymes phenylalanine ammonia-lyase, beta-1,3-glucanase, and chitinase were also assayed. Their higher activities in the selected resistant wild species and lower activities in the highly susceptible ones were found. This suggests the possibility that these enzymes are not only constituents of resistance but also could be used as biochemical markers for screening Compositae wild species for alternaria leaf spot resistance.