Pre-breeding research to
support sustainable farming of
onion
Andrew Taylor
Research Fellow
Introduction
•  Onion is an important crop in the UK and worldwide
•  In 2008, 76 Mt of onions were produced worldwide
(0.36 Mt in the UK)
•  Onions are widely consumed and deliver potential
health benefits provided through compounds such
as quercetin and cysteine sulphoxides
Value of
onions in
UK
Year
Area harvested (ha)
Value (£million)
2008
10,277
78.7
2007
10,446
108.0
2006
10,389
94.6
FAOSTAT- Food and Agriculture Organisation of the United Nations, http://faostat.fao.org/
Objectives of onion work
•  Screen an onion diversity set and develop
a further understanding of the genetic
control of:
1.  Resistance to Fusarium oxysporum
2.  Response to AMF
3.  Seed and seedling vigour traits
Onion diversity set
•  96 accessions sampled from the Warwick
University GRU
•  Seed produced for 10 half sib families for each
accession
•  DNA extracted from 1 half sib family per accession
Fusarium basal rot
•  Fusarium oxysporum f. sp. cepae is a
soilbourne fungus causing basal rot in onion
•  Currently one of the biggest problem for UK
onion growers and set producers
•  Likely to become a greater problem with
current UK climate change models
1. Resistance to Fusarium
oxysporum
•  Glasshouse based seedling screen developed
•  Seeds soaked in a spore suspension for 1
hour prior to sowing
•  Disease symptoms (mortality) scored over a 4
week period
•  10 commercial onion varieties screened for
resistance using seedling screen
•  6 different Fusarium isolates assessed for
aggressiveness
Highly susceptible variety
FUS2 (aggressive
isolate)
Partially resistant variety
Control
1. Resistance to Fusarium
Resistance/susceptibility of
10 commercial varieties
100
Percentage survival/control
90
80
70
60
50
40
30
20
10
0
A
B
C
D
E
F
G
H
I
J
Onion variety
1. Resistance to Fusarium
Aggressiveness of 6 isolates
100
Variety A
Variety B
90
Percentage survival/control
80
70
60
50
40
30
20
10
0
A1.2
A3.1
FUS1
FUS2
NL151
NL262
Fusarium isolate
Moderate isolate
Aggressive isolate
1. Resistance to Fusarium
Glasshouse Bulb Trial
•  Two onion varieties
  Variety A – susceptible
  Variety B– partially resistant
•  Two Fusarium isolates
  Aggressive and moderately aggressive
•  Seedlings transplanted into Fusarium-infested
compost
•  Grown to bulb stage
•  Scale of symptoms on bulb recorded
1. Resistance to Fusarium
1. Resistance to Fusarium
Symptoms at bulb stage
Variety A
Control
Variety A
Inoculated
Variety B
Control
Variety B
Inoculated
1. Resistance to Fusarium
Symptoms at bulb stage
Moderate isolate
Aggressive isolate
1. Resistance to Fusarium
Screening the diversity set- seedling screen
1. Resistance to Fusarium
Arbuscular Mycorrhizal
Fungi (AMF)
•  Colonise plant roots and increase
nutrient uptake, particularly P
•  AMF also help protect plants from
pathogens in the soil
•  Onion-AMF interactions are common
due to the shallow root system of the
plant host
2. Response to AMF
•  Trial carried out to assess growth and
nutritional effects of AMF on onion
•  10 lines from onion diversity set
•  5 different AMF isolates and a mixed
community of all 5 used as inoculum
•  Carried out in low P soil
G.intraradices
G.manihotis
2. Response to AMF
2. Response to AMF
Dramatic growth effects
Mixture
G.manihotis
G.intraradices
G.mosseae
G.versiforme
A.spinosa
2. Response to AMF
10
8
7
6
5
Line 1
4
3
2
1
0
Glomus
mosseae
Glomus
manihotis
Glomus
versiforme
Glomus
Acaulospora
intraradices
spinosa
Mixture
4.5
4
Line 2
Shoot dry weight/control
Shoot dry weight/control
9
3.5
3
2.5
2
1.5
1
0.5
0
Glomus
mosseae
Glomus
manihotis
Glomus
versiforme
Glomus
Acaulospora
intraradices
spinosa
Mixture
2. Response to AMF
Further AMF work
•  AMF colonisation leads to increased N,
and P levels as well as decreased Ca, K
and Mg levels
•  Response appears to be consistent
across diverse onion lines
•  Trial in progress:


Response of entire diversity set to AMF
Response to AMF in high/low P soil
2. Response to AMF
3. Seed and seedling vigour
traits
•  System developed based on Brassica
work (Bill Finch-Savage, University of
Warwick)
•  Germination and initial growth rate of
both shoot and root
•  Upward growth in strong soil
•  Currently completing diversity set
screens
Germination/initial growth rate
3. Seed and seedling vigour
Germination/initial growth rate
210
170
150
130
shoot
110
90
70
50
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Line
290
root
Time to 2cm (hrs)
Time to 3cm (hrs)
190
270
250
230
210
190
170
150
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
Line
3. Seed and seedling vigour
Summary and Future work
•  Onion diversity set developed
•  Diversity currently being screened for
agronomically important traits
•  Putative sources of Fusarium resistance
identified
•  Future work:
  Complete diversity set screens
  Genotypically screen the diversity set using
SNP and gene-specific markers
Acknowledgments
VeGIN project:
University of Warwick:
•  Dave Pink
•  Brian Thomas
•  John Clarkson
•  Gary Bending
•  Paul Hand
•  Nicole Pereira
•  Bill Finch-Savage
•  Heather Clay
•  Andrew Mead
•  Julie Jones
•  Viktoria Vagany
•  Andy Jukes
•  Matthew Mitchell
•  Joan Yurkwich
University of
Wisconsin:
•  Mike Havey
www2.warwick.ac.uk/fac/sci/lifesci/research/vegin/onion
andrew.taylor@warwick.ac.uk