Written by Dr. Andrew Taylor at the University of Warwick. This is the report from a BSPP Junior Fellowship.
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Fusarium oxysporum f. sp. cepae is a soilborne fungus which causes basal rot of onion. Fusarium basal rot is already a significant problem for onion growers both in the UK and worldwide. Current climate change models predict increases in global temperatures which would exacerbate this problem.
We are currently carrying out phenotypic screens on 96 onion lines and plan to combine this data with genotypic data which will be obtained by screening this diversity set using SNP markers. The original plan for this trip was to spend 2 weeks working with Professor Mike Havey and the University of Wisconsin in Madison. However, the trip was planned to also coincide with the National Allium Research Conference (NARC) which was being held in Reno, Nevada.
University of Wisconsin, Madison (30th November-7th December)
The first week of my visit was spent in Madison where I visited Professor Mike Havey and other researchers at the University of Wisconsin. I learnt a great deal about the onion breeding programmes at the university and exchanged ideas on screening onions for Fusarium resistance. Prof Havey and his co-workers previously used a seedling screening method which is the preferred option for us as it allows for high throughput screening of large numbers of onion lines. Following this visit, a future collaboration has been agreed which will involve sending bulbs of potentially Fusarium resistant onion lines to Prof Havey to be grown to flower. These plants will then be either self-pollinated or crossed with other potentially resistant lines. A portion of the seed from these crosses will be sent to us for future Fusarium resistance trials at the University of Warwick.
Professor Havey and his team are currently developing and mapping SNP markers in onion. They will then use an Illumina chip to SNP genotype onion lines from a mapping population. Following this visit, it was agreed that we will send Prof Havey DNA from 10 lines selected as the most Fusarium resistant from phenotypic screens of our onion diversity set. These DNA samples will then be included on the Illumina chip. This will allow us to search for markers for Fusarium resistance in onion. I also met with Professor Irwin Goldman, another onion breeder. Professor Goldman developed a Fusarium resistant onion line in the 1970’s and it may be possible to obtain seed/bulbs from this line.
During my week in Madison, I also visited the Monsanto/Seminis research station in DeForest, Wisconsin. I met with Lowell Black, a plant pathologist who has a great deal of experience of working with Fusarium in onion. I observed the setting up of Fusarium resistance trials. The trials are carried out in highly controlled growth chambers, with tight control on temperature, humidity and light levels which allows for greater repeatability between runs. I also learnt of an alternative method for Fusarium storage, utilising silica gel. We hope to use this link to facilitate the future exchange of both onion lines and Fusarium isolates.
National Allium Research Conference (NARC), Reno (8th-10th December)
Following my trip to Madison, I flew to Reno for the NARC. This was a very interesting meeting and many useful contacts were made. A large part of the meeting focussed on Iris Yellow Spot Virus (IYSV) in onion. This virus is spread by thrips and is currently the biggest issue for onion growers across the USA. There is currently a large, multi-state project underway which aims to identify methods to control IYSV. Interestingly, this virus has not been reported in the UK but may be a future problem to be wary of. Mike Havey is one of the many people involved in IYSV research and he is targeting onion lines with semi-glossy foliage, a phenotype which slows the build up of thrips on the onion plants. Professor Havey also gave a talk on sequencing the onion genome, calling for an international effort towards a full genome sequence.
Many bacterial diseases of onion were also discussed. Of these, centre rot caused by Pantoea ananatis seems to be a problem which is on the increase. Christine Hoepting of Cornell University presented a simple but effective solution involving reduced plant spacing. Brenda Schroeder from Washington State University spoke on the management of Enterobacter cloacae, a pathogen which causes storage rot in onion. This is a particular problem as it causes discolouration of the inner bulb scales with no outer symptoms and is an opportunistic human pathogen. I gave an oral presentation on our Fusarium work at this conference. This was received with a great deal of interest from both researchers and plant breeders as Fusarium in onion is a global problem.
New Mexico State University, Las Cruces, New Mexico (13th-15th December)
The final leg of my US trip was to visit Chris Cramer at New Mexico State University in Las Cruces. Dr Cramer has been working on Fusarium in onion for 13 years so this was a very useful visit. I observed field trials in progress and exchanged ideas on screening for Fusarium resistance in onion. Dr Cramer favours a bulb inoculation method as it appears to be more repeatable than a seedling test. Such a test involves cutting the basal plate of a mature onion bulb and inoculating with an agar plug containing Fusarium. Dr Cramer is another person who is involved in the work on IYSV. I was able to see a field trial in progress which was set up to screen onion lines for resistance to IYSV.
This trip was very useful for both current and future development of our research into Fusarium resistance in onions. Many thanks to the BSPP for providing the funds for such a productive trip.
Dr. Andrew Taylor
University of Warwick