Resumen
Gremmeniella abietina causes shoot dieback and stem cankers on conifers throughout Northern hemisphere. The aim of this study was to investigate the virulence of Turkish G. abietina isolates in a field experiment. The lower branches of 15-20-year-old P. nigra and C. libani in a plantation site at 1,050 m a.s.l. in Isparta were inoculated at 1-2-month intervals during September-January. Five isolates obtained from high altitude mountainous forests were used. Each isolate was inoculated into two branches per tree and repeated ten times on both tree species at each inoculation date. The branches were sampled at the end of February, and in August, and lesion lengths in the inner bark measured. The mean lesion length on P. nigra and C libani were 10.6 ± 0.8 and 3.8 ± 0.2 mm in February and 17.6 ± 1.4 and 7.8 ± 0.8 mm in August, respectively. Differences in the mean lesion length between the isolates were small. Nevertheless, there were significant differences between the isolates on P. nigra in November and January inoculations, and on C. libani at all four inoculation times. The mean lesion lengths for all isolates at both sampling dates was the highest (p < 0.01) in December inoculations for both P. nigra (22.0 ± 1.9 February; 32.9 ± 2.9 August) and C. libani (5.6 ± 0.7; 11.3 ± 1.2). There was no difference between the September and January inoculations on P. nigra, despite the almost six-fold difference in incubation period. During the December inoculations, the trees were most likely in winter dormancy, i.e. unable to defend themselves, which would explain the large lesions.