Water stress and Sphaeropsis sapinea as a latent pathogen of red pine seedlings

. The role of water stress in the initiation of collar rot by Sphaeropsis s apinea in asymptomatically colonized Pinus resinosa seedlings is reported. . Mortality and frequency of identification of the pathogen was quantified for seedlings subjected to different water regimes or watering regime-fungi cide (benomyl) combinations in glasshouse experiments. . In experiment 1, seedling mortality ranged from 8% of repeatedly watered seedlings to 50% of those in the driest regime; data analysis indicated a h igh probability that mortality was not independent of watering regime. Seed lings developed symptoms resembling those of Sphaeropsis collar rot, and S. sapinea was identified from living (42%) and dead (92%) seedlings. In expe riment 2, mortality of repeatedly watered seedlings was low, irrespective o f fungicide application. For nonwatered seedlings, however, mortality was g reater among seedlings not treated with fungicide (61%)than among benomyl-t reated seedlings (37%); data analysis indicated a high probability that mor tality was not independent of fungicide treatment. . Sphaeropsis sapinea can act as a latent pathogen; physiological alteratio n, through water stress, can effect release from the quiescent condition to result in rapid disease development.