. 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.