Dose-Response Relationships of Five Conifers to Infection by Conidia ofGremmeniella abietina

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Abstract
Seedlings of 5 coniferous species were tested for their relative susceptibility to an isolate of the European strain of G. abietina. In June 1979, seedlings of each species were sprayed to runoff with distilled water or with suspensions containing 102, 103, 5 .times. 103, 104, or 105 conidia/ml. Percent infection was determined in 1980, and survivors plus some replacement seedlings were reinoculated in June of that year. Effects of the 2nd inoculation were determined in 1981. In both years, the order of susceptibility was Pinus resinosa > P. strobus > Picea glauca and P. abies. Disease incidence in Pinus sylvestris was not significantly different from P. strobus in 1980 but was much higher in 1981. Low disease incidence in P. sylvestris in 1980 was attributed to reduced shoot growth (thus, fewer potential infection courts) after transplanting in 1979. For each Pinus species, increased inoculum resulted in increased disease. Disease incidence was so low in Picea spp. at all inoculum levels that no relationship of inoculum dose to disease incidence could be identified. Where G. abietina was found on Picea spp., it may have been a weak parasite or saprobe.