Vegetable Genetic Improvement Network
(VeGIN)
Screening for resistance to Fusarium basal rot in onion
A. Taylor, J. Clarkson, D. Pink and B. Thomas.
Warwick Crop Centre, School of Life Sciences, University of Warwick, Wellesbourne, Warwick, CV35 9EF, UK. Andrew.Taylor@warwick.ac.uk
Onion diversity set
Onion diversity produced by the creation of half sib families
from 96 divergent lines
Lines selected to cover phenotypic and geographic diversity (see
Fig. 1)
Includes wild Allium species and Allium fistulosum
Diversity set screened for resistance to Fusarium oxysporum,
response to arbuscular mycorrhizal fungi and seed/seedling
vigour
Figure 1: Example of diversity in the onion diversity set
Fusarium basal rot in onion
Figure 2: Symptoms of Fusarium basal rot on onion
Caused by the soilborne fungus Fusarium oxysporum f. sp. cepae
A global problem favoured by warm temperatures
Currently one of the biggest problems for UK onion growers and set
producers
Fungus infects the roots and basal plate causing a bulb rot (Fig. 2)
Causes symptoms at every stage of plant development leading to severe
economic losses
Currently no completely resistant cultivars and limited chemical control
Screening for resistance to basal rot
100
90
Relative percentage survival
Developed a rapid seedling assay to screen for resistance (Taylor
et al., 2012)
Results of seedling assay verified using a mature plant assay
where symptoms of basal rot on mature bulbs are recorded
A range of resistance/susceptibility was observed amongst
commercial onion cultivars (Fig. 3)
Higher level of resistance observed within the diversity set using
the seedling assay (Fig. 4)
Resistance confirmed using mature plant assay (Fig. 5)
80
70
Red- Hystar
Green- Ailsa Craig
60
50
40
30
20
10
Relative percentage survival
100
0
90
Onion line
80
Figure 4: Resistance to basal rot in the onion diversity set measured using a seedling assay
70
60
50
inoculated
control
inoculated
control
40
30
Susceptible
20
10
0
Figure 3: Susceptibility to basal rot in commercial onion
cultivars (Taylor et al., 2012)
Conclusions
Sources of Fusarium resistance have been identified using a
newly developed seedling assay and confirmed using a mature
plant assay
Current work involves genotyping the onion diversity in search of
genetic markers associated with resistance
Resistant
Figure 5: Resistance to basal rot at the seedling and bulb stages.
Key Reference
 Taylor, A et al. (2012) Identification of differential resistance to six Fusarium oxysporum f. sp. cepae isolates in
commercial onion cultivars through the development of a rapid seedling assay. Plant Pathology, in press.
Warwick Crop Centre
www.warwick.ac.uk/go/wcc