RESISTANCE OF GRAFT-COMPATIBLE AND GRAFT-INCOMPATIBLE PSEUDOTSUGA-MENZIESII ROOTED CUTTINGS TO PHELLINUS-WEIRII

One-year-old rooted cuttings taken from 23- and 26-year-old graft-comp atible and graft-incompatible Pseudotsuga menziesii (Mirb.) Franco wer e inoculated with one of three isolates of Phellinus weirii. After 20 months in a greenhouse, infection frequency and severity were signific antly greater in the graft-incompatible cuttings. Cellulose concentrat ion in the root tissue was higher in graft-incompatible than graft-com patible cuttings. Concentrations of lignin, phenolic compounds, and ta nnins were higher in graft-compatible than graft-incompatible cuttings . Cellulose concentration had a positive linear correlation (r2 = 0.84 ) with the P. weirii infection rating. The concentration of phenolic c ompounds and lignin in secondary root tissues was negatively correlate d with the infection rating (r2 = 0.73 and 0.84, respectively). The li gnin/cellulose and phenolic/cellulose ratios were negatively correlate d with the infection rating of P. weirii infection in a linear relatio nship (r2 = 0.82 and 0.77, respectively). White-rot fungi cannot use t ree defense compounds, such as lignin and phenolics, as the sole energ y source; an alternate energy source is necessary to degrade these com pounds. The lignin/cellulose and phenolic/cellulose ratios in the root s may be important measurements to explain the host-pathogen response of P. weirii infection.