Pre-breeding research in onion:
screening an onion diversity set
for beneficial traits
Dr Andrew Taylor
Research Fellow
Project objectives
• 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 Crop
Centre Genetic Resources Unit
• Including LD, ID and SD cultivars
• Includes A.roylei, A.vavilovii and A.fistulosum
• Seed produced for 10 half sib families for each
accession
• DNA extracted from 1 half sib family per
accession
Owa
Greenella
White Sweet Spanish Jumbo
Guardsman
Auxonne
Moravanka
Red Wetherfield
Sarand
The Kelsae
Rossa di Firenze
www2.warwick.ac.uk/fac/sci/lifesci/research/vegin/onion
Fusarium basal rot
• Fusarium oxysporum f. sp. cepae is a
soilborne fungus causing basal rot in onion
• Found on onions throughout the world
• Currently one of the biggest problems for UK
onion growers and set producers
• Likely to become a greater problem with
current climate change models
• Can cause damage at every stage of plant
development
1. Resistance to Fusarium oxysporum
Symptoms of basal rot
1. Resistance to Fusarium oxysporum
Screening for resistance to
Fusarium oxysporum
• Glasshouse based seedling screen developed
• Seeds soaked in a spore suspension for 1
hour prior to sowing
• Plant death scored over a 4 week period
• Glasshouse based screen on mature plants
developed
• Involves transplanting seedlings into
Fusarium-infested compost
• Two tests produce comparable results
1. Resistance to Fusarium oxysporum
Seedling screen
1. Resistance to Fusarium oxysporum
Resistance in commercial
onion cultivars
90
80
Percentage survival
70
60
50
40
30
20
10
0
Taylor et al. 2012, Plant Pathology, in press
1. Resistance to Fusarium oxysporum
Resistance in the diversity set
90
80
Relative survival (%)
70
60
50
40
30
20
10
Line
Susceptible control
Partially resistant control
1. Resistance to Fusarium oxysporum
Confirming resistance- mature plant screen
1. Resistance to Fusarium oxysporum
Confirming resistance- mature plant screen
2
1.8
Mean symptom score
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
70
SD 1
SD 2
SD 3
SD 1
SD 2
SD 3
SD 4
Plant death (%)
60
50
40
30
20
10
0
SD 4
+ 6 plants dead prior to harvest
1. Resistance to Fusarium oxysporum
Arbuscular Mycorrhizal Fungi
(AMF)
• Colonise roots and help increase nutrient
uptake
• Can increase yield, improve resistance to
pathogens and increase drought tolerance
• Onion diversity set screened for mycorrhizal
responsiveness
2. Response to AMF
Screening the diversity set
for response to AMF
• Glasshouse based trial
• Irradiated field soil (low P) inoculated with a
single AMF species
• Onion seedlings transplanted into inoculated
soil
• Growth and nutritional responses recorded
after 10 weeks
• 15 lines tested in low and high P
2. Response to AMF
Highly responsive
95
Screening the diversity set
for response to AMF
90
Mycorrhizal dependency (%)
85
80
75
70
65
60
55
50
Lower response
Onion line
2. Response to AMF
Growth effects
Highly responsive
Control
Lower response
Inoculated
Control
Inoculated
2. Response to AMF
High P vs. low P
2
1.4
1.8
1.2
1.6
1
1.4
1.2
0.8
1
0.8
0.6
0.6
0.4
0.4
0.2
0.2
0
0
control low P
control high P
Inoc low P
Inoc high P
2.5
control low P
control high P
Inoc low P
Inoc high P
control low P
control high P
Inoc low P
Inoc high P
1.4
1.2
2
1
1.5
0.8
0.6
1
0.4
0.5
0.2
0
0
control low P
control high P
Inoc low P
Inoc high P
2. Response to AMF
Seed/seedling vigour
• Important for crop establishment and
uniformity
• Tests developed based on Brassica work (Bill
Finch-Savage, Warwick University)
• Diversity set screened for seed/seedling vigour
• Two tests of vigour- germination/initial growth
rate and emergence in compact soil
3. Seed/seedling vigour
210
Screening the onion diversity
set for seed/seedling vigour
Time for root to reach 3cm (hrs)
190
170
150
130
110
90
70
Onion line
3. Seed/seedling vigour
Is there a correlation between
vigour and Fusarium
resistance?
Time for root to reach 3cm (hrs)
190
170
150
130
110
90
R² = 0.1762
70
50
0
20
40
60
Fusarium resistance (% survival)
80
100
Summary and current work
• Onion diversity set developed and screened for
agronomically important traits
• Sources of Fusarium resistance identified
• Different levels of response to AMF observed
• Highly vigorous lines identified
• Current work:
 Confirming sources of Fusarium resistance
 Genotyping the diversity set using SNP
markers
Acknowledgments
VeGIN project:
University of Warwick:
• Dave Pink
• Brian Thomas
• John Clarkson
• Gary Bending
• Paul Hand
• Nicole Pereira
• Andrew Mead
• Julie Jones
• Viktoria Vagany
• Andy Jukes
• Matthew Mitchell
• Joan Yurkwich
University of
Wisconsin:
• Mike Havey
• Warwick Crop Centre GRU & Horticultural Services
www2.warwick.ac.uk/fac/sci/lifesci/research/vegin/onion
andrew.taylor@warwick.ac.uk