The sweet chestnut (Castanea sativa) is a very important tree species in Europe. It can be utilized in different ways. Its nut is a very healthy food and its valuable wood has diverse utility. It has a key role in supporting the economic capacity in rural areas. The processing of its fruit, wood and by-products has nearly 1000 related end-products.
In 25 European countries, it can be found on more than 2 million hectares. The European production has decreased by one-third (currently 270.000 tons/year). The economically important pests of the chestnut are mainly introduced parasites. Most important is the blight fungus. This parasite has affected the areas suitable for chestnut growing, presenting heavy difficulties for the growers.
The chestnut blight fungus (Cryphonectria parasitica) is the most serious introduced pathogen to the European chestnut. The fungus, a canker organism, infects bark, cambium and causes die back and mortality of infected trees. The fungal pathogen was introduced into Italy in 1938. Without any professional treatments against this pathogen, it threatens total destruction of chestnut populations.
One of the factors motivating my research on C. parasitica is the potential for biological control of the pathogen with viruses; this phenomenon is known as hypovirulence because virus-infected fungal strains are less virulent and do not kill chestnut trees. Hypovirulent isolates were discovered in Switzerland in the late 1960s. These recovering trees were shown to harbour C. parasitica isolates that were less virulent (the isolates grew in chestnut but much more slowly allowing the tree to wall-off the fungus with callus tissue). It was determined that the agent responsible for the reduced virulence was a virus (mycovirus). The causal agent of hypovirulence is a large dsRNA (12.7 kb) in the cytoplasm of the host fungus, which has both open reading frame (ORF) A and ORF B fragments. Hypovirulence in C. parasitica is considered a model system for control of plant pathogens with mycoviruses.
My scientific work was motivated by the fact that I have seen many sick trees in my country. During the study of the professional literature, I discovered how serious efforts are being made to save already infected forests and plantations. My idea is that the production of pre-immunized propagating material can be an additional advantage in the fight against the pathogen, and can be carried out in an environmentally friendly manner without pesticides.
To implement the project successfully and to prove the viability of the innovation idea, I have planned to implement 3 different tasks:
1. Task: Fungus/virus analysis (2 months). Molecular methods will be utilized to study hypovirulent strains of the chestnut blight fungus. Complementary DNA of the large dsRNA with reverse-transcription will be used to examine the genetic variability of the mycovirus by comparing their RFLP-profile. Sequencing of ORF-A and ORF-B fragments of the Cryphonectria hypoviruses will show similarity/differences among dsRNA molecules.
2. Task: Hypovirulent inoculum (1 month). Production of hypovirulent inoculum with in vitro propagation. Dormant chestnut stems will be used to verify pathogenicity of hypovirulent isolates (21 days). After the isolates are verified to be hypovirulent (based on molecular methods and pathogenicity tests), mass inoculum will be produced for field applications.
3. Task: Optimization of field applications (9 month). Detailed information regarding hypovirulent strains, the time of application, classification of healing cankers will be assessed.
As a starting point for my BSc research, I studied the professional literature on the pathogens, took part in the collection of infected bark samples and the creation of laboratory cultures of the chestnut blight fungus.
The result of the proposed research would be to produce “immunized” seedlings that carry the hypovirulent type of the pathogen and are suitable for transplantation into the infected environment. Protection is due to the survival of the hypovirulent form of the pathogen for a long time (with no plant damage) and the ability to block any infection of the virulent fungal strains that may occur. The survival of the hypovirulent type of the pathogen on trees can be measured exactly as well as it affects to the growth of the young plant.
László Radócz,, Hungary