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- Natural spread of mycoviruses a puzzling and dazzling issue for biocontrol of chestnut blight by Cryphonectria HypovirusPublication . Gouveia, Maria Eugénia; Moura, Luísa; Coelho, ValentimMycoviruses are widespread viruses in filamentous fungi considered ubiquitous in all groups. Cryphonectria hypovirus 1 (CHV1) of the Hypoviridae family is included in the genus Hypovirus. Hypovirus are well-studied biological control agent of chestnut blight a lethal disease of Castanea sativa Mill. Unlike many mycoviruses, which are cryptic or latent in their host, CHV1 reduce virulence, reduce pigmentation and sporulation and induce female sterility in its host the Cryphonectria parasitica fungus. Chestnut blight was introduced in Portugal and rapidly became a severe lethal disease in all chestnut regions in the 90’s. Initial epidemics had a very rapid spread and no or few cases of hypovirulence was reported. Besides scientific issues are obtained therapeutic hypovirulence was introduced as a biological control to mitigate disease impact. Later, in 2013 chestnut blight appears in scattered stands of the coast north Minho region where natural spread is the dominant way of hypovirulence spread. In this study we investigate and specifically addressed the question of the massive natural spread of hypovirulence. We studied vegetative compatibility system (vic genes) of the host fungus, presence and characterization of CHV1 subtypes and hypovirus transmission capacity, issues that play a key role in hypovirus spread. Although some different results are obtained major key determinants and driven forces to improve natural hypovirus spread are still unclear and new approaches as (HTS) high throughput sequencing will be valuable to understand the driven forces of natural dissemination that will greatly increase field sustainability of therapeutic applications of hypovirulence and chestnut recovered
- In vitro antagonism evaluation of endophyte Chaetomium aureum against Cryphonectria parasiticaPublication . Coelho, Valentim; Machado, Júlia Melo; Guerra, Inês; Gouveia, Maria EugéniaThe European chestnut tree (Castanea sativa Mill.) is threatened by various microfungi that affect its production. In the trunk and branches infected by chestnut blight (Cryphonectria parasitica (Murril) Barr.) it was observed the presence of several microfungi that co-occur in the presence of the disease among which the endophytic fungus Chaetomium aureum Chivers. Many species of the genus Chaetomium are described as antagonists of plant fungi and various soil microorganisms, and the secondary metabolites of these species exhibit biological activities. The aim of this work was to study the antagonist activity of the fungus C. aureum against C. parasitica. The study was carried out under in vitro conditions by establishing co-cultures in PDA culture medium. Five repetitions were performed for each co-culture and the inner and outer radius of the colonies were measured for 10 days. The mycelial growth inhibition was expressed as percentage growth inhibition in relation to the control co-culture. The reduction of growth of the internal radius of C. parasitica by C. aureum was significant (P=0.02) after 10 days with an inhibition of 36.8%, and no contact was observed between colonies. This study highlights the importance of phytobiome in controlling chestnut trunk and branch diseases and the need to continue screening for fungal isolates that are candidates for natural disease control on chestnut.
- Spatial dynamics of chestnut blight disease at the plot level using the Ripley’s K functionPublication . Azevedo, João; Coelho, Valentim; Castro, João Paulo; Spínola, Diogo; Gouveia, Maria EugéniaWe used the Ripley’s K function to describe the spatial dynamics of chestnut blight (Cryphonectria parasitica (Murrill) Barr) in sweet chestnut orchards to look at pattern in the pathogen distribution over time and the effect of the location of infected trees on the pattern of disease spread. We used data on infected and dead trees in 2003, 2004, 2005, and 2009 in 4 orchards located in Curopos parish, Portugal. We found both random and aggregated patterns of infected trees in the beginning of the study period and significant association of infected trees between successive dates, particularly at short distances. Two of the 4 studied orchards showed significant clustering of infected and dead trees in any of the dates observed but random spatial pattern in the remaining two which can possibly be explained by both natural propagation of the disease and management practices.
- Short and long term efficacy and prevalence of Cryphonectria parasitica hypovirulent strains released as biocontrol agents of chestnut blightPublication . Coelho, Valentim; Nunes, Luís; Gouveia, Maria EugéniaChestnut blight, Cryphonectria parasitica (Murrill) Barr, was reported in Portugal in 1989. The disease rapidly spread within the chestnut region of the Trás-os-Montes (the Northeast of Portugal). Eradication and mechanical/burning exclusion failed to control the disease and natural hypovirulence is still absent or of very low incidence. The introduction of human-assisted therapeutic hypovirulence is therefore required to control the disease. We presente here the efficacy of field applications (short and long term) of a locally characterized hypovirulent strain (CHV1-RBB111), by the punch method in two chestnut orchards (Valpaços and Vinhais). The Valpaços disease incidence was 68% (65 out of 96 trees) and in Vinhais it was 46% (78 out of 169 trees). In both locations, diversity of vegetative incompatibility (vc type) was low and largely dominated (> 85%) by a single vc type (EU11). In Valpaços, all cankers of the orchard were treated (63 cankers) and in Vinhais 31 trees (cankers) were treated. One year after application, field efficacy was very high with 93.8% of healed cankers in Valpaços and 90.3% in Vinhais, these values increased to 100% and 93.5% (respectively) after four years. The persistence of the introduced CHV1-RBB 111 strain was high and present in almost all treated cankers and it was dominant both inwards and on the application site revealing an endophytic behavior. The non-C. parasitica microfungi were abundant with 14 different species. Biscogniauxia mediterranea (De Not.) Kuntze was the most abundant in both orchards. Treatment with the introduced hypovirulent strain (CHV1-RBB111) was found to be effective in controlling chestnut blight with regeneration of cortical tissues and recovery of treated trees.