Resisting the
currant-lettuce aphid
Rosemary Collier, Warwick Crop Centre, School of Life Sciences Currant-lettuce aphid
Nasonovia ribisnigri
•  Heteroecious - primary winter woody host and secondary
summer herbaceous host
•  Holocyclic - asexual and sexual reproduction
•  Possibly anholocyclic sometimes surviving on lettuce and
other related hosts including chicory, speedwell and
hawkweed
Control
•  Feeding location makes control difficult
•  Currently:
–  Insecticides with several different modes of action e.g.
•  Imidacloprid seed treatment
•  Systemic insecticide spirotetramat (Movento)
–  Resistant lettuce varieties
•  Introduced in 1998
•  Introgressed a resistance gene (Nr) from the wild
lettuce species L. virosa into commercial varieties
of the cultivated lettuce L. sativa
Resistance-breaking aphids (Rb)
•  Reported first in 2007 in continental Europe
•  Investigated by breeding companies
–  Rb Nasonovia developed on all lettuce varieties with Nr gene
–  Rb Nasonovia multipy more slowly than WT aphid on lettuce
with no Nr gene
–  No significant differences between Rb aphids originating in
France or Germany
•  Now in the UK
Research on Nasonovia at Warwick
•  HDC project: Biology and
control – Gemma Hough
•  HortLINK project: Control
with pesticides and
biopesticides
•  VeGIN: Identifying sources
of resistance in diversity
set
Technique:
•  Infest test plants with fixed numbers of new-born nymphs
•  Cover plants with bread bags
•  Count aphids after a specific period of time
Survival of WT and RB aphids – Gemma Hough
Development time of WT and Rb aphids at
different temperatures – Gemma Hough
50
45
5 °C
Development t ime t o adult (days)
40
10 °C
35
15 °C
30
20 °C
25
25 °C
20
15
10
5
0
Rb Aphid + Saladin
(Sus)
Rb Aphid + Eluarde
(Nr)
Rb Aphid + Rotary
(Nr)
WT Aphid + Saladin WT Aphid + Eluarde WT Aphid + Rotary
(Sus)
(Nr)
(Nr)
Aphid t ype (Rb or WT) and lettuce variety (Sus or N r)
At lower
temperatures
a few WT
aphids
overcome
resistance
Number of WT aphids recovered from tests on
lettuce diversity set after 3 weeks (5 at start)
Mean t otal number oper plant
500
400
300
Mapping parent
200
100
0
95 96 14 85 92 93 87 2 62 71 1 84 22 37 60 38 61 57 8 54 64 5 9 51 40 10 24 32 81 42 68 16 70 17 73 15 36 3 77 59 43 56 35 29 58 34 86 25
Range: 1.4 – 442 aphids per plant
Number of WT aphids recovered from tests on
lettuce diversity set after 3 weeks
Mean t otal number per plant
600
500
400
300
200
100
0
21 7 75 90 63 13 88 26 30 31 11 44 4 67 74 91 12 28 33 23 78 52 79 69 47 18 41 49 39 50 89 6 80 83 76 82 48 19 45 46 53 72 66 20 94 55 65
Range: 1.4 – 442 aphids per plant
Number of Rb and WT aphids recovered from tests
on lettuce diversity set after 3 weeks
450
Mean total number per plant
400
350
300
250
200
150
100
50
0
95 96 14 85 92 93 87 2 62 71 84 37 60 38 61 57 8 54 64 5
9 51 40 10 24 32 81 42 68 16 70 17 73 15 36 77 59 43 56 35 29 58 34 86 25 27
Wild type aphids
Resistance-breaking aphids
Number of Rb and WT aphids recovered from tests
on lettuce diversity set
1400
Mean total number per plant
1200
1000
800
600
400
200
0
21 7 75 90 63 13 88 26 30 31 11 44 67 74 91 12 28 33 23 78 52 79 69 47 18 49 39 50 89 6 80 83 76 82 48 19 45 46 53 72 66 20 94 55 65
Wild type aphids
Resistance-breaking aphids
Future work
•  The most resistant line was the wild species L. virosa. If
a mapping population was available – then this could be
followed up to map the resistance.
•  Failing that a backcross programme could be initiated –
we have SNPs for all wild species.
Future work
•  Based on the screen, one of our mapping parents showed some
resistance – this will need to be confirmed
•  The mapping population could be used to map the resistance. There
may be transgressive segregation for the trait in the population –
meaning some lines may perform even better than the resistant
parent
•  With the new SNP markers being genotyped in the population we
can then map the trait using a new linkage map, and get informative
markers that can be used for marker assisted selection in
subsequent generations
•  These markers are linked to sequence so these will aid the mapping
process
•  The markers have also been screened in the Salinas x Serriola
(Michelmore) population, the alignment of common markers will
open up the wealth of genomic resources at UC Davis
Chicory and endive screen
(Peter Walley & Gemma Hough)
21 Chicorium instybus and 29 Chicorium endivia
Aphid numbers (Endive and Chicory)
1000
900
800
700
600
500
400
300
200
100
0
50
9 46 13 47 37 25 26 38 27 45 32 31 33 36 48 44 35 39
7 16 43
6 20 49 41 22 40 19
3 10 30
Thank you to:
Defra
Horticultural Development Company
Gemma Hough
Peter Walley
Marian Elliott