Chancro en castaño: hongos implicados en la enfermedad y estrategias de control de "Cryphonectria parasitica"

Abstract

The European chestnut (Castanea sativa), an ecologically and socioeconomically important species, is being seriously damaged by chestnut blight disease. Since the detection of its main causal agent, the fungus Cryphonectria parasitica, in 1947 in Spain it has been observed in different areas of the country. In Asturias it was detected in 1982, and since then it has spread rapidly, declining the Asturian chestnut stands. Previous experiences of disease control in Europe, were based on biological control using hypovirulent fungal isolates which contain the virus Cryphonectria hypovirus CHV-1 that attenuates the fungal virulence. From Asturian chestnuts with healing or healed chestnut cankers sampled, C. parasitica isolates were obtained and classified as potentially hypovirus-free or hypovirus-infected according to morphological criteria. After their molecular characterization, the CHV-1 hypovirus infection was verified in all potentially hypovirus-infected isolates, and two subtypes (E and D) were indentified. The ecological fitness of subtype D, only reported in Germany, as biological control agent, is known, whereas the suitability of subtype E, already reported in Spain, is unknown. The presence of hypovirulent isolates compatible with the dominant types of vegetative compatibility (vc) and the low diversity of vc types in this region, favours the application of biological control. Treatments with CHV-1-D could therefore be initiated, whereas the CHV-1-E efficiency should be researched. On the other hand, the chemical control has not been considered a viable alternative due to its environmental impact and the shortage of authorized treatments. Nevertheless it was observed that the agrochemical epoxiconazol has a certain effectiveness against C. parasitica so it could be useful in particular situations such as in the production of plants in nurseries. Thus it is not rejected that the chemical control, under managed conditions, could be part of the integrated therapeutic strategy against the disease. Besides C. parasitica, there are two pathogenic fungi which produce cankers on chestnut trees, Sirococcus castaneae and Gnomoniopsis castaneae. From some cankers, together with C. parasitica, Diplodina castaneae was isolated and was morphologically and molecularly characterized, and then taxonomically reclassified as S. castaneae. In chestnut plants with similar symptoms, G. castaneae was also isolated. The finding of both species in Asturias means their first detection in Spain. It is unknown if they are a new introduction or if they could have previously been unnoticed and together with C. parasitica be responsible for the chestnut blight disease in our region and/or country.