A Conducive Day Concept to Explain the Effect of Low Temperature on the Development of Scleroderris Shoot Blight

Publisher Website
Google Scholar
Abstract
The in vivo growth of Gremmeniella abietina at -6 c both in the presence or absence of ice crystals was confirmed. Red pine seedlings artificially inoculated with the North American serotype, exposed to natural field conditions and artificially manipulated field conditions, developed symptoms of Scleroderris shoot blight when exposed to 44 or more days in which the temperature remained between -6 and +5 C or snow completely covered the seedling or tree parts-a conducive day. Thus, an extended period of relatively mild canopy temperature during the winter appears to favor disease development. The conductive period-a period in which 44 or more conducive days occurred-could either occur in the winter after inoculation, or over the two winters after inoculation. The apparent latent period in the disease cycle may result from the need for winter conditions before symptom development can occur. The occurrence of symptoms primarily on lower branches, and the restriction of the disease to latitudes that receive sustained snow cover in the Lake States are consistent with this observation. Comparison of literature descriptions of outbreaks of the disease to weather records revealed a strong association between conductive periods, usually single conducive winters, and the occurrence of symptoms. The natural range of the disease may be restricted by the need for recurrence of conducive periods within 3 yr. to avoid breaking the disease cycle.