In trials the oilseed rape variety Alegria from Grainseed was number 3 out of 30 varieties in terms of Verticillium Index and, with its other benefits of good overall disease resistance and excellent vigour, it could be a useful variety for growers to consider.
Colin Button, Seed Manager for national distributor Hutchinsons, has been conducting Verticillium trials for 4 years and explains the background to this unique project. “In 2010 one of our agronomists in Lincolnshire had a crop of oilseed rape that unexpectedly collapsed at harvest. It was difficult to understand why, so we brought in a plant pathologist from ADAS who diagnosed Verticillium wilt at very high levels. It was the first time we had seen this disease at such devastating levels and we have subsequently used this site for trials to assess Verticillium resistance. This year, 2014, the trials are hosted by ADAS Boxworth. Initially oilseed rape breeders were a little reluctant to submit their varieties for evaluation, because they had not observed discernable differences in resistance up to that time, but now we have most of the major breeders submitting varieties as they see the disease spreading. The trials set out to establish usable differences between varieties using a Verticillium wilt Index, which indicates disease expression in the crop. The lower the Index, the better. This information is useful to direct growers in the future, if this disease gets progressively more widespread.”
In the 2013 trials, the rape variety Alegria had a Verticillium Index of 29.9, compared with Catana, which is the reference variety for Verticillium resistance, which had an Index of 28.5. Alegria was the third lowest scoring variety, showing it has natural tolerance to this disease. Alienor, also from Grainseed, was 7th out of the 30 varieties tested with an Index of 44.8. The worst variety had a Verticillium Index of 83 and Excalibur, the reference variety for susceptibility to this disease, was 77.1.
“We have seen Alegria in trials for two years now. It is one of a group of new varieties that has good standing power, early maturity and good overall disease control, including Verticillium, which is what growers are looking for,” says Colin.
According to the HGCA Crop Monitor, 24% of winter oilseed rape crops were infected with Verticillium wilt in 2013. In 2012 it was 10% and in 2011 18%. It is found in all regions except the South West. Highest levels of disease were in the South East where 58% of crops had infection and 8% of stems affected.
Colin Button reminds growers that Verticillium wilt symptoms can only be seen at the end of the crops’ life, so it is worth going out to inspect crops prior to harvest, (and look at the post - harvest stubbles) which is any time now, to look for premature ripening of stems or smaller branches. “If there is high inoculum, dry and warm soils and a susceptible variety, there could be an outbreak of Verticillium at any time. So if you know you have high disease pressure, use a variety with proven resistance.”
Neil Groom, Technical Director for Grainseed advises growers to consider growing rape varieties with a good combined disease resistance package. “And this means good known resistance to Verticillium and Phoma as well as to Light Leaf spot. Alienor has a 7 rating for Phoma stem canker and a 6 rating for Light Leaf Spot, giving it an excellent overall disease resistance package. Alegria has a 7 rating for Phoma and a 5 for Light Leaf Spot. Genetic resistance to Phoma and Verticillium in these varieties is multi-gene and so unlikely to break down.”
“Experts are advising growers that Verticillium is best managed through growing resistant varieties and through better agronomy. They also warn that growing susceptible varieties in disease-affected area could lead to a build-up of microsclerotia in the soil. Alienor and Alegria show good resistance to Verticillium as well as exceptional vigour which will help them grow away from diseases and pests, even more important this year with no neonicotinoid seed treatments,” says Neil.