Botrytis cinerea and Norway spruce seedlings in cold storage.

摘要

The risk of grey mold damage on first-year Norway spruce seedlings during cold storage was studied using conidia inoculation on spruce seedlings with different inoculation times and microclimate conditions (surface wetness, temperature, relative humidity) before storing. The temperature dependence of germination and germtube growth of Botrytis cinerea conidia at low temperatures was tested in vitro. The germination of Botrytis cinerea spores in vitro reached 100% in 15 hours at 6 degrees C, and in about 52 hours at 0 degrees C. The length of the germtube in 52 hours was seven times longer at 6 degrees C than at 0 degrees C. These results indicate that the main progression of grey mold occurs in the beginning and/or thawing phase of cold storage. In the three inoculation experiments the cold storage temperature was about -3 degrees C and the seedlings were stored in cardboard boxes. Uninoculated seedlings in the same boxes with inoculated seedlings had a higher disease incidence than the seedlings in boxes with no inoculated seedlings. Inoculation performed 7, 4 or 1 days before cold storage caused more disease before cold storage the earlier the inoculation was carried out. During cold storage the disease frequency doubled or increased even more. The treatment at 6 degrees C, 80-90% relative humidity and surface wetness immediately before cold storage seemed to increase the number of diseased needles on the top of shoot more than the treatments at 2 degrees C and at 6 degrees C with 60-70% relative humidity and surface wetness. The proportion of seedlings with bud burst showed a strongly negative correlation with the number of diseased needles at the top of the shoot at the end of storage. According to the results of this study, especially a high relative humidity with surface wetness on the seedlings and temperatures a few degrees above zero in the beginning of cold storage favour grey mold damage. The experiments indicate that B. cinerea is a potential storage pathogen for Norway spruce seedlings even though the seedlings are, in late autumn, relatively resistant to this pathogen if not additionally stressed..