The chestnut blight disease

Cécile RobinINRA Bordeaux , France

Chestnut blight symptoms

Cortical lesions

Cankers

Death of the top of the tree

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

Aux Etats-Unis

First reported in the USA, in 1904 on American chestnut

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

Routes of invasions of C. parasitica

Allways through plant or wood introduction!

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

Thank you for your attention