Abstract:

Inoculations revealed that the Chinese isolates of Sphaeropsis sapinea were similar to American A isolates in pathogenicity which was much nore aggressive than B isolates.Type B isolates could also penetrate host without wounding,but with lower incidence than type A.During the periods of shoot elongation and needle development the fungus could directly enter the current year shoots and eventually kill them,then with shoot maturation,the role of wounding was gradually shown up,and inoculations of nonwounded shoots resulted in no symptoms or only some necrotic needles.The fungus could also enter needles through stomata.It could infect and kill twigs through wounds on the 2^nd or the 3^rd year node.Pinus tabulaeformis,P.densiflora and P.densiflora var.zhangwuensis were more disease resistant than Pinus sylvestris var.mongolica,and P.densiflora var.Zhangwuensis showing a sort of disease tolerance.Young trees of Pinus sylvestris var.mongolica were more disease resistant than old ones.After inoculation shoots weakened by girdling showed symptoms more rapidly and severely than non weakened ones.The durations of incubation and reproduction were related to host species,tree vigor,maturity of host tissue, and air temperature,etc.

Key words: Sphaeropsis sapinea, Pathogenicity