ABSTRACT
In this chapter, the authors review the evidence that the nature of chestnut blight has changed due to biological intervention in chestnut stands in Europe and America. Since several reviews on the recovery of trees in Europe already exist, they concentrate on the situation in North America, with emphasis on Michigan. The authors also include a section on how these findings may be exploited to the betterment of the American chestnut tree, and our understanding of host/parasite interactions. Simply stated, a culture is hypovirulent when the capacity to cause disease is reduced from the expected. A working definition that is more specific for the chestnut blight system has become accepted by most researchers. In the case of hypovirulence, a close correlation is based on the presence of specific double-stranded ribonucleic acid (dsRNA) segments, specific phenotypic characteristics, concerted transfer of both dsRNA and associated phenotype, and curing experiments where elimination of specific dsRNA segments is correlated with changes in phenotype.
