Responses in the bark of Cupressus sempervirens clones artificially inoculated with Seiridium cardinale under field conditions

By 70 days after inoculation, resistant and tolerant clones of field-grown Cupressus sempervirens restricted penetration of the bark by Seiridium card inale, forming ligno-suberized boundary zones which included four to six la yers of cells with suberized cell walls. This response contrasted with that in susceptible clones, where only two to four layers of suberized cells we re formed in discontinuous bands around inoculation sites. Detection of mul tiple layers of thin suberized boundary zones in susceptible clones indicat ed repeated penetration of the wound/infection-induced barrier by S. cardin ale during a single growing season. The methods described will be valuable in the development of rapid, early and accurate screening programmes for du rable resistance to Seiridium canker in Cupressus species.