Walnut blight symptoms - Cost 873

Factors influencing walnut blight
symptoms emergence
and development
Study already presented on the 6th International Walnut Symposium - Melbourne 2009 –
Australia
A. Chevallier 1 , O. Bray 1 , JP. Prunet 12 , M. Giraud 2
Experimental results in 2008
Presented by Jean-Loup Péroys 1
1
Station Expérimentale de Creysse - Perrical - 46600 Creysse – France – http://pro.wanadoo.fr/stationdecreysse
2
Centre Technique Interprofessionnel des Fruits & Légumes - Centre de Lanxade - 24130 La Force - France

Creysse Experimental Station
South-western
Walnut
production
area
COST 873 – Costiera 2009 - Italy

Context & Objectives
WALNUT BLIGHT
1 st disease of walnut trees in France
Up to 50 % losses by walnuts drops
Caused by Xanthomonas arboricola pv. Juglandis (Xaj)
Copper = only allowed product to fight the disease. BUT : low efficacy
Huge variability of sensitivity to walnut blight observed between
orchards of a same cultivar
Lack of knowledge on this disease
QUESTIONS & GOALS
Link between Xaj populations / phenological stages of walnut trees /
climate / walnut blight symptoms development
Does fungus play a role in blight symptoms
Identify and understand factors that affect the sensitivity of trees to
walnut blight
COST 873 – Costiera 2009 - Italy

Materials & Methods
Orchard name Bouscarel Soursac
Walnut blight
sensitivity
Place
+ + >> - -
Creysse
(Dordogne valley)
≠
Queyssac-les-Vignes
(limestone plateau)
Cultivar Franquette = Franquette
Date of plantation 1995 ≈ 1993
Density 11 x 11 = 11 x 11
Pruning formation gobelet = gobelet
Soil
soft deep sandy soil
(pH 6.5)
≠
heavy shallow clay soil
(pH 8)
Fertlization 100 % chemical ≠ 100 % organic
Irrigation Sprinckler under canopy ≠ Dripper system
Chemicals
treatments
None = None
COST 873 – Costiera 2009 - Italy

Materials & Methods
20 trees / orchard followed for :
Walnut blight symptoms emergence and evolution on
15 walnuts / tree : localization and intensity of the necrosis
Xaj populations on buds, leaves, female flowers, pollen
and fruits (collaboration with Ctifl and university of Girona)
Fungi on buds, female flowers and necrotic nuts
Climate: T°C, RR, RH (1 weather station close to each orchard)
Soil moisture (Watermark® probes)
Phenolic compounds quantity measured in leaves
during July with Dualex® (Force A inc.)
Tree vigour: trunk circumference
COST 873 – Costiera 2009 - Italy

Results : Walnut blight symptoms
***
***
***
NS
‣ A higher sensitivity of
Bouscarel trees to WB
NW = Necrotic walnuts
‣ Most of necrotic
walnut drops
occurs 1 month
after female
flowering
COST 873 – Costiera 2009 - Italy

Results : Xaj epidemiology
log (cfu+1/g)
log (cfu+1/organ)
‣ Dormant buds = storage place for Xaj during winter
‣ Pollen = good way for its dissemination
‣ More Xaj on flowers and fruits on the sensitive orchard Bouscarel
COST 873 – Costiera 2009 - Italy

Results : Xaj epidemiology
‣ No difference between orchards
‣ Xaj population = epiphytic
COST 873 – Costiera 2009 - Italy

Results : Fungi
‣ Complex: Alternaria,
Fusarium and
Colletotrichum found
in WB necrosis in
2007
‣ Complex found in
buds in 2008
‣ The complex was not
found on flowers
COST 873 – Costiera 2009 - Italy

Results : Fungi
‣ Complex not found in WB necrosis in 2008
‣ Xaj were more frequent
‣ Fungi = secondary contamination
Blight losses: Bouscarel >> Soursac
Xaj populations: Bouscarel > Soursac
Fungus populations: Bouscarel = Soursac
COST 873 – Costiera 2009 - Italy
Which factors influence these
differences

Results : Climate influence
NS
*
NS
NS
NS
NS
No correlation between :
‣ total precipitations /
WB symptoms
emergence or
necrotic walnut
drops
COST 873 – Costiera 2009 - Italy

Results : Climate influence
NS
NS
*
NS
NS
NS
No correlation between :
NS
NS
NS
NS
NS
NS
‣ mean temperature /
WB symptoms
emergence or
necrotic walnut
drops
‣ mean relative
humidity / WB
symptoms
emergence or
necrotic walnut
drops
COST 873 – Costiera 2009 - Italy

Results : Soil moisture
COST 873 – Costiera 2009 - Italy

Results : Soil and management practices influence
Huge differences of soil
Soil characteristics Bouscarel Soursac
% Clay 12,5 % 57,8 %
% organic mater 1,28 % 3,26 %
pH 6,57 8
CaO (g/kg) 1,41 9,19
CEC* Metson (Cmol+/kg) 3,7 22,45
* Cation Exchange Capacity
Opposite management practices
• Mature sheep manure brought every year since plantation on Soursac orchard
• Mineral fertilization on Bouscarel orchard,
• Soursac has never been spaying with chemicals in contrast with Bouscarel
Influence on tree vigour
<
Orchard
Trunk mean
circumference (cm)
Mean annual growth
since plantation (cm)
Bouscarel 91,85 ± 7,8 a + 6,1 a
Soursac 72,8 ± 4,6 b + 5,6 b
‣ Less vigour = less sensitivity during growth => hardiest trees
COST 873 – Costiera 2009 - Italy

Results : Trees’ phenolic compounds
Dualex unit (quantitative)
3
2,5
***
***
2
1,5
1
B ous carel
S ours ac
0,5
0
Flavonoids
P henolic c ompounds
Hydroxycinnamic acids
‣ Higher concentration of flavonoids and HCA =
better resistance towards WB
‣ Influence of soil and orchard management on
phenolic compounds
COST 873 – Costiera 2009 - Italy

Conclusion
Climate
Xaj & fungus
populations
Management
practices
Phenolic compounds
& tree physiology
Blight
sensitivity
- Fertilization
- Soil enrichment
- Irrigation
- Chemical treatments
- Pruning
Soil
-Type
- Organic mater quantity
- Water supply
- Cations Exchange Capacity
COST 873 – Costiera 2009 - Italy

Questions
WB Symptoms assessment:
• Unusual symptoms
Climate:
• Leaf wetness ; thermal amplitude ; sunshine duration... need to be tested
Xaj Epidemiology and fungus:
• Fungus = secondary contamination
• Why do we have no fungus and Xaj in more than 50 % of necrosis
Soil water supply:
• Which water pressure threshold to define tree stress (with Watermark® probes)
Phenolic compounds:
• Period of study = too short. Need to do it during the whole season,
• Are flavonoids and HCA the good phenolic family to test / WB
• Correlation between phenolic contains in leaves and fruits
• Do Dualex® measures fit to walnut trees
COST 873 – Costiera 2009 - Italy

Thanks for your attention