An observatory network to monitor the durability of genetic resistance against rhizomania in the Pithiviersregion

1. Frédéric Boyer – 06/06/2018
1
An observatory network to monitor the durability of genetic
resistance against rhizomania in the Pithiviers region
76th IIRB Congress, Deauville, 05-07 June 2018

2. 2
Rhizomania: a major soil-borne viral disease
• Viral disease caused by Beet necrotic
yellow vein virus (BNYVV) and
vectored by the soil-borne protist
Polymyxa betae
• Considered as the most damaging
pathogen for sugar beet along with
beet cyst nematode in France
• Identified in France for the first time in
1970 in Alsace and in 1977 in the
South of Paris (Loiret region)
Electron micrograph of rod-shaped virions of BNYVV
Central Science Laboratory, York (GB)

3. Stunting and wilting of a susceptible variety (3 left rows)
compared to a resistant one (3 right rows) – May 2018
3
Rhizomania symptoms in the field
Constriction of the taproot Constriction and lignification of the
taproot + bearding

4. 4
Genome structure and function of BNYVV
BNYVV genome is constituted of 4 to 5
positive strand RNAs:
• RNA1 and RNA2 are required for
“housekeeping” functions: replication,
packaging, movement and regulation
• RNA4 is required for transmission of
the virus by its vector P. betae
• RNA3 and RNA5 are involved in
pathogenicity (through proteins p25
and p26 that act in a synergistic
fashion) and resistance breaking
Pavli et al., 2011
Gilmer. Tamada, 2016

5. 5
The French P-type BNYVV
• Now classified as A-II type according to
CP, p25, p26 and p31 sequences
 P-type BNYVV contains extra RNA5
• Beets infected with P-type BNYVV
show systemic symptoms and
increased plant mortality
• In France, P-type BNYVV was originally
found in a small area near Pithiviers
 Expanding up North
Dispersion of the P-type BNYVV in France – Galein, 2013
Systemic symptoms
on an infected leaf

6. 6
Resistant varieties deployed in the South of Paris
• Single resistance conferred by the locus Rz1
• Double resistance conferred by the loci Rz1 and Rz2 (Rz2 provides better
efficiency in limiting virus replication than Rz1)
 Synergistic action conferring a higher level of resistance
De Biaggi et al., 2010

7. 7
Resistance-breaking events in the Pithiviers area
• Loss of Rz1 resistance can be
associated with:
– Mutations in a tetrad of amino-
acids (position 67-70) on protein
p25 (RNA3)
– The action of p26 (RNA5)
together with p25
• Resistance-breaking events
are increasing every year in
the South of Paris, therefore
increasing the use of double
resistant varieties
Events of resistance breaking
Historic events
New events detected in 2017

8. 8
Monitoring the durability of genetic resistances: setup
• 28 plots in rotation (beginning 2009-
2011)
• 3 genotypes/plot: Rz1 (V1), Rz1 (V2)
and Rz1 Rz2
• Monitoring on minimum 3 rotations
• Preliminary results on 16 plots due to a
lack of Rz1 Rz2 genotypes also
resistant to beet cyst nematode
29m limite de propriété
borne 55 RD44
cultures voisines31m
bande de roulement
ro
3m 3m 3m 3m3m 3m 3m 3m 3m 3m3m 3m 3m 3m 3m
54m
2èmesemoir
3m 3m 3m
101
10m
102 103
2èmesemoir
2èmesemoir
203
5m
201
10m
202
10m
302 303
5m
PLAN 991 AL (2011/2018) - Rhizomanie forte - BOYNES La Tombelle
LEWINIA BEETLE FORTISSIMA
PULVE
401
10m
402 403
5m
301
Rz1 (V1) Rz1 (V2) Rz1 Rz2

9. 9
Scales used for rhizomania symptoms evaluation
Healthy plant :
normal taproot
Diseased plant :
taproot constriction
Severely diseased plant :
necrosis of the taproot
Less than 5% of
diseased plants
More than 5% of
diseased plants
More than 10% of
severely diseased plants
Healthy plot Diseased plot Severely diseased plot

10. 0
2
4
6
8
10
12
14
16
Point zero 1st rotation
1
0
13
10
2
6
Evolution after 1 rotation for 16 plots selected for analysis
10
Rhizomania infestation levels in the network
4 plots
0
2
4
6
8
10
12
14
16
Point zero
8
16
4
Situation with 28 plots at point zero
Average rotation time = 4 years

11. 11
Comparison of overall genotypes behavior after 1 rotation
Average results on 16 plots
0,0
10,0
20,0
30,0
40,0
50,0
60,0
70,0
80,0
90,0
100,0
Point zero 1st rotation
81,0
64,6
15,6
25,1
3,4
10,2
Rz1 (V1)
0,0
10,0
20,0
30,0
40,0
50,0
60,0
70,0
80,0
90,0
100,0
Point zero 1st rotation
82,7 78,6
15,6 19,4
1,8 2,0
Rz1 (V2)
0,0
10,0
20,0
30,0
40,0
50,0
60,0
70,0
80,0
90,0
100,0
Point zero 1st rotation
94,9 95,4
4,7 3,9
0,4 0,6
Rz1 Rz2

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Focus : genotypes behavior on a single plot (Champart -
Mondreville) after 3 rotations
0
10
20
30
40
50
60
70
80
90
100
Point zero 1st rotation 2nd rotation
100
79
71
21
13
16
Champart - Rz1 (V1)
0
10
20
30
40
50
60
70
80
90
100
Point zero 1st rotation 2nd rotation
100
66
88
34
12
Champart - Rz1 (V2)
0
10
20
30
40
50
60
70
80
90
100
Point zero 1st rotation 2nd rotation
100 96 93
4 7
Champart - Rz1 Rz2

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Conclusions and perspectives
• On a monitoring perspective :
– Rz1 Rz2 genotypes are still resistant to rhizomania after 1 rotation and
behave much better than Rz1 particularly in situations with severe
rhizomania infestations
– Observations in Champart suggest that resistance is still effective after 2
rotations
– This network (of 16 plots + 12 remaining) will allow us to rapidly detect a
breakdown of Rz1 Rz2 resistance in situations with severe rhizomania
pressure
• On a research perspective:
– Stored lateral roots and soil could be used for studying BNYVV genetic
diversity and evolution

14. 14
Acknowledgements
• Pierre Houdmon (ITB Loiret)
• Anne-Laure Chambenoit & Hugues Bergamini (ITB Loiret)
• Henri de Balathier (ITB Ile-de-France)
• Fabienne Maupas (ITB Paris)

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THANK YOU FOR YOUR ATTENTION