Biological Control of Chestnut Blight in Portugal

Hypovirulence is a specific biological control method of chestnut blight, a lethal disease of American and European chestnut. The causal pathogen of chestnut blight is Cryphonectria parasitica, a fungus of Asian origin and an A2 quarantine organism in Europe. The disease has been reported since 1990 in Portugal, one of the last European countries where the pathogen was introduced. The chestnut blight fungus is now well established and widespread in Portugal with fast expansion in all chestnut regions. Biological control with hypovirulent strains of C. parasitica is considered an efficient means to control the disease and improve chestnut recovery. One of the goals of this study is to apply hypovirulence as a biological method for chestnut blight control and produce a solid scientific base to extend the treatment method over the country’s chestnut areas. A successful biological control program will have a very high practical impact on crop productivity and on the social perception of applied research. Field records and studies included parameters related to trees (dendrometric parameters and plant health status) and the physical characteristics of the plots (type of soil, exposure, geographic coordinates, age of trees, actual management of soil, etc.). Other scientific issues related to population structure of the pathogen include evolutionary forces that are present or dominate at population level (clonality, selfing, self-incompatibility, vc type structure, vc type segregation, CHV presence, CHV species). One of the goals of this study is to generate data that can answer questions dealing with the effect of the founder population and the driving forces on actual and future chestnut populations. The study also can produce an innovative and a realistic approach that has potential for large and extended field application with a positive impact on chestnut production. INTRODUCTION In spite of the decline of chestnut areas from 80,000 ha in the 1950s to 45,000 ha in 2013, chestnut production remains crucial in Portugal. Chestnut production is most important on Denomination Protected Regions: Castanha da Padrela, Castanha da Terra Fria, and Soutos da Lapa. However, there are biotic constraints that impact chestnut production; these include two diseases of chestnut, ink disease (Phytophthora cinnamomi) and chestnut blight (Cryphonectria parasitica). Chestnut blight was first detected in Europe in 1938 but it was not introduced to Portugal until the 1990s. The disease has expanded rapidly in all chestnut growing regions in Portugal. Recent surveys in areas where the disease was previously recognized revealed an increase in disease incidence ranging from 40-100% (Azevedo et al., 2010; Bragança et al., 2009). A large number of newly infected sites, coupled with increased disease resistance has greatly increased the loss in chestnut fruit production has led to the decline and death of many chestnut trees. Biological control utilizing hypovirulence, a virus-mediated attenuation of fungal pathogenesis, is an efficient mean to control the disease and improve chestnut recovery (Heiniger and Rigling, 1994; Robin and Heiniger, 2001; Cortesi et al., 1996).