Symptoms caused by a fungus, Cryphonectria parasitica
incubation
Ascospores in perithecia:sexual reproduction,
rain dispersal
infection
Spores in pycnidia:asexual reproduction,air dispersal
latency
dispersal
Perenial cankers
Life cycle of C. parasitica
History
Reported in Europe (in Italy) in 1938
Devastating epidemics in C. sativa forests and orchards
Aux Etats-Unis
Actual distribution in Europe
Detected eveywhere in Europe except in Cyprus, Latvia, Lithuania, Luxembourg, Iceland or Norway
History
• 1964: reports of healing trees
• Discovery of the virus (CHV1) whichcauses the hypovirulence in C. parasitica
• Virus-infected isolates of C. parasitica– Can infect trees but cause superficial cankers
– Have a lower dispersal activity
– Can be recognised in culture
Infected isolates (HV)Non infectedisolates (V)
Natural regulation of chestnut blight
• CHV1 is still absent or its incidence is very low in some areas in some recently infested areas, such as northern France, northern Switzerland and Portugal, north-western Spain
• Diversity of CHV1:
different strains of CHV1 have been characterized, some of them are more effective to induce healingof cakers and to be transmitted
Impacts of chestnut blight
• Disease incidence:– from 67 to 99 % in Italy– from 17 to 65% in Portugal– 78.5 % in north-western Spain– still in expansion
• Direct effects:– loss of production, mortality,
failures in grafting…– much less severe than in the USA,
fruit and wood production are maintained in regions wherehypovirulent is established
– interactions with other stresses: drought, gall wasp, ink disease
-
• 1989-1997• 1997-2006• 2006-2012
Strategy for biological control for chestnutblight using CHV1 infected isolates
From scientific questions to applied objectives:
• Transmission in the fief of CHV1
– When can I deploy viral strains to obtain an efefctivecontrol of the disease?
– How can I deploy viral strains?
• Phenotypic diversity of CHV1– Which viral strains can I deploy?
Transmission of the CHV1
No extracellular form of the virus
No vectorMultiplication in
fungus A
Vertical transmission
Conidia of A
Horizontal transmission
Fungus B
Ascopores:
Virus-free
Horizontal transmission is possible between infected and non-infected strains C. parasitica which are compatible.
Similar vegetative
compatibility type (vc type) Different vc types
Transmission of the CHV1
CHV1 strains can spread in C.parasitica populations with low diversity of vc types.
We must know the vc types occurring in each country to study and use CHV1.
Vc type distribution
In France (2001)In Europe (2001)
Recent research has been done in the different coutries (for examplePortugal, Germany…).
Strategy for biological control for chestnutblight using CHV1 infected isolates
• Transmission in the fief of CHV1– When can I deploy viral strains to obtain an efefctive
control of the disease?
When C. parasitica population diversity is known, at the regional level.
– How can I deploy viral strains?
Virus-infected strains of C. parasitica are deployed.
Strategy for biological control for chestnutblight using CHV1 infected isolates
• Phenotypic diversity of CHV1– Which viral strains to deploy?
To obtain quick healing of cankers : viral strainswith strong effect on the fungus but lowdispersal ability
To reduce the density and impact of C.
parasitica populations without continuous human assistance: viral strains with mild effecton the fungus but high dispersal ability
.
Strategy for biological control for chestnutblight using CHV1 infected isolates
In Portugal, since 2014: IPB (Instituto Politécnico de Bragança) is the coordinator of the program and the producer of the hypovirulent strain.Farmers associations and chestnut farmers are partners of the process.
Cf stand at the 1st logistics, person contact Eugenia Gouveia.
In France (since the 7O’s):Deployment of hypovirulent isolates in orcahrds, with up to 5 isolates (different vctypes) in one mixture. Each region has a specific mixture.Virus-infected strains are inoculated on infected trees. The strains are sold by BIOTISA
New methods for deployment have been suggested:
use of segments of chestnut wood inoculated with virus-infected C. parasitica strains in forests ( Prospero et al. 2006)use of different viruses which could recombine and be more effective (Feau et al. 2014)
Hopes in a genetic control
• Variability in resistance in chestnut blight does exist
• Evaluation tests do exist: stem inoculations, leafinoculations
• Some resistance mechanisms are known
• Studies are under progess to understand geneticdeterminism
– (Portugal, Cf Carmen Santos’ communication,
France…)
– USA
Clone Genotype Use
Code Name
114 Belle Epine C. sativa Fruit variety
159 Rootstock
4 C. crenata Rootstock
7 Marsol Rootstock
15 Marigoule Rootstock
48 Précoce Migoule C. crenata x C. sativa Fruit variety
74 Maraval Rootstock
90 Ferosacre Rootstock
112 Bournette Fruit variety
118 Marlhac Rootstock
119 C. sativa x 4 Rootstock
122 Marissard Rootstock
125 Bouche de Betizac Fruit variety
21 Rootstock
72 C. sativa x hyb. Rootstock
92 Rootstock
94 Rootstock
34 Rootstock
52 (C.crenata x C.sativa) x hyb Rootstock
54 Rootstock
60 Rootstock
85 Rootstock
89 C.mollissima x C.sativa Rootstock
Perspectives
• Biocontrol does work, but not every where and not everytime
• C. parasitica vc types and CHV1 distribution data should begathered in a common data base in order to optimize and facilitate biocontrol with CHV1.
• An integrated control system should be developed to stem the course of the blight fungus and reduce damages. The combined use of hypovirulence and blight resistance may produce effective blight control.
• Synergism between diseases: such an integrated system should also take into account the gall wasp and ink disease, which both interact with chestnut blight.
• Collaboration between European research teams is needed