J. Genet. & Breed. 51: 269-277 (1997) Canker resistance stability of some Cupressus sempewirens clones to Seiridium cardinale A. Santini, N. Casini, V. Di Lonardo and P. Raddi' Centro di Studio Patologia Specie Legnose Montane, C.N.R. - Piazzale delle Cascine, 28 - 50144 Florence, Italy Received September 30, 1996 ABSTRACT The stability of the acanker resistance~ character of 50 cypress clones located at two different sites, was investigated by a parametric approach. Cankers derived from artificial inoculations were scored and variation in the data was analyzed to evaluate the effects of clone, site and clone x site interaction. By means of the coefficient of variability and Wricke's ecovalence, the intraclone vari- ability and the variability of the individua1 clones with respect to al1 the clones tested were demon- strated. The leve1 of resistance of the clones varied according to site, therefore suggesting Mezt in the absence of a sufficiently stable character, it does not seem appropriate to direct research towards determining aunive_rsallyr resistant clones. Key words: Coefficient of variability, Cypress canker, Seiridium cardinale, Wricke's ecovalence. INTRODUCTION The resistance of the cypress tree (Cupressus sempervirens L,) to cortical canker is due to its post-infectional capacity to comportmentalise in- fections of Seiridium cardinale (WAG.) SUT~ON and GIBSON (MORIONDO, 1972; RADDI and PANCONESI, 1977; PONCHET and ANDREOLI, 1990). It has already been recognized that the progression of the pathogen and the epidemic diffusion of the dis- ease are strongly influenced by pedoclimatic con- ditions (ANDREOLI et a l , 1984; MADAR et al., 1989; PANCONESI, 1990; SANTINI et al, 1994). RADDI and PANCONESI (1984; 1991) observed different re- sponses in ramets of the sarne clone even at the same site. Research has however allowed the se- lection of resistant clones, which have been .- patented for commercialization (PANCONESI and - RADDI,1990; 1991). Conservation of the aresistantx character over time and space is an essential pre- requisite for their commercial success. However, the cypress tree demonstrates resistance of a poly- genic type which seems to be less likely to be sta- ble over space than over time (AGRIOS, 1988). For these reasons, the genetic improvement programs for the cypress have involved experi- mentation at various sites with at least 10 ram- ets per clone selected, in order to identify whether there may be superior clones that are cuniversallyn resistant, that is, that function in al1 kinds of environments (RADDI and PANCONES 1991; SANTINI et a l , 1994). The objective of this work is to generate in- formation on the stability of the acanker resis- tantn character of cypress clones characterized by differing degrees of resistance, in two sites that differ in terms of pedoclimatic conditions. MATERIALS AND METHODS The study was carried out on 50 clones of C. sem- pewirens, deriving from plants selected from natural- ized stands in Tuscany in accordance with the IUFRO sampling rules. The clones were characterized by varying degrees of susceptibility and were grafted on- to l -year-old seedlings. In 1983, in two (8,000 m2) plots, 16 ramets per clone were positioned in 16 rows, 50 plantslrow with a growing space of 3m x 3m. The plots were sur- rounded by a single row of artificially inoculated ram- ets of severa1 susceptible clones. The two sites were: (i) Cannara (42It59'N; 12"34'E; 195m elevation) in the Province of Perugia, Italy, with ' Corresponding author: Piazzale Cascine, 28 - 50144 Firenze, Italy, Fax ++3955 354786 - E-mail: raddi@ipaffi.cnr.it