Tullio Turchetti

Monitoring diseases of chestnut stands by small format aerial photography

Abstract Italian chestnut stands located near Montepastore (Bologna‐Italy) were selected as a test area for aerial ‐photographic monitoring. An Ultra Light Motorplane (U.L.M.) and small format aerial color‐infrared (CIR) photography were used to survey the plants. The vegetative condition of the chestnut trees and diseased plants were identified. Dead and severe damaged trees were clearly detected on photographs and mapped. Ground surveys and lab tests confirmed the presence of ink disease caused by Phytophtora cambivora (Vein) Buiss. and chestnut blight caused by Cryphonectria parasitica (Murr.) Barr on the trees. Results indicated that low altitude CIR aerial photography obtained from U.L.M. may be a relatively inexpensive tool to assess stress conditions in chestnut orchards.

Corticolous mites (Acari) as potential vectors of Cryphonectria parasitica (Murr.) barr hypovirulent strains

Abstract Specimens of four species of corticolous mites, Liebstadia humerata Sell. (Oribatida: Protobatidae), Scheloribates latipes (C. L. Koch) (Oribatida: Scheloribatidae), Thyreophagus corticalis (Mich.) (Acaridida: Acaridae), and Zygoribatula laubieri meridionalis Trave (Oribatida: Oribatulidae), were found in cankers, caused by Cryphonectria parasitica on chestnut trees, and were reared on laboratory cultures of the parasite. Monoxenic cultures were carried out using a hypovirulent (H) strain of the blight fungus. A group of mites was transferred from the H cultures to a met auxotrophic virulent (V) strain. Fecal pellets collected aseptically were used to inoculate agar plates. New C. parasitica cultures developed and white colonies with the morphological characters of the hypovirulent strain were obtained. Development of C. parasitica from mites indicated that the mycelial fragments were viable. The dsRNA presence in these cultures obtained from fecal pellets deposited by mites feeding from the blig...

Thyreophagus corticalis as a vector of hypovirulence in Cryphonectria parasitica in chestnut stands

The natural spread of hypovirulence in Cryphonectriaparasitica (Murr.) Barr. occurs in chestnut (Castanea sativa Mill) stands and orchards in Italy and other European countries, leading to spontaneous recovery of the diseased trees. Little is known about how hypovirulence spreads in chestnut stands but various corticolous mite species frequently detected on chestnut cankers could be one of the many factors playing a role in the spread. Artificial virulent cankers created in inoculation field tests and treated with Thyreophagus corticalis (Acari, Sarcoptiformes, Acaridae) raised on hypovirulent cultures showed similar growth to those treated with mycelia of the hypovirulent strain over 18 months of inoculation. Cultures re-isolated from virulent cankers treated with mites were found to contain hypovirus like those derived from pairings of virulent and hypovirulent strains. Viral dsRNA could be carried externally and/or ingested by mites from the hypovirulent mycelia and then transmitted to the mycelia of virulent strains, causing their conversion. In a laboratory study, all fecal pellets collected from mites reared on hypovirulent and virulent strains grown on semi-selective media gave rise to colonies of C. parasitica with similar morphological characters and virulence to the original cultures. Field inoculation of stump sprouts with the resulting colonies revealed that mite digestive tract passage did not alter the virulence of the studied strains. These results are of interest for the biological control of chestnut blight.

Biological control and management of chestnut diseases

Chestnut blight and ink diseases caused, respectively, by Cryphonectria parasitica and Phytophthora cambivora and P. cinnamomi, are revised. The main strategies for efficient biological control and management are discussed, considering their appearence, symptomatology, epidemics and the actual situation. The types of cankers of chestnut blight are shown, as well as the characters of the different types of infection caused by C. parasitica. The evolution of the diseases and the spread and effectiveness of hypovirulence traits are revised, considering the morphology, physiology, presence and transmission of dsRNA. Chestnut resistance, and the role of environmental and other ecological factors in ink disease, including the action of the soil microflora, are discussed. The role of silviculture and the evaluation of biological control strategies for blight and ink disease management are also revised. The improvement of the management of chestnut disease needs a better understanding of the ecological dynamic of chestnut ecosystems. An holistic approach including all the factors involved in the chestnut trees ecology is proposed in planning the management of such ecosystems and in undertaking the best measures of conservation and improvement.