This fall we have received a number of calls regarding downgrading of seed based on a Fusarium Damaged Kernel (FDK) test. In order to address this, we are re-running this popular article from last year regarding the difference between an FDK and disease testing and the importance of both.
In the fall of 2010 many farmers were concerned that their cereal seeds had a pink discoloration, which could mean Fusarium graminearum.
Although weather conditions were favorable for the increase of F. graminearum, infection levels stayed relatively steady in the seed we examined compared to the previous crop year. There were a few very hot spots in southern Alberta, but I think the message of using an integrated approach to disease control, including the use of a seed treatment, is getting through to everyone because I would have expected higher infection levels, given the year we had.
But growers still need to be careful. All foliar diseases were on the rise this year. In cereals, pathogens such as Septoria, Pyrenophora, Cochliobolus and Fusarium sp. (foliar leaf blotches and common root rots), as well as weaker pathogens (Epicoccum, Alternaria and Cladosporium) were all on the rise in 2010 when compared to previous, drier years. A rise of many diseases simultaneously in one growing season can make seed health diagnosis very challenging. The incidence of so many diseases at once can mask the actual presence of F. graminearum, so testing must be thorough to be sure.
For example, if you usually rely on a visual analysis, such as an FDK (Fusarium Damage Kernel) test, you may have higher than normal percentage diagnosis. Why? Because higher Epicoccum sp. infection can discolor seed to purplish/reddish/orange/pink hues, a lot like F. graminearum. Similarly, the septoria complex of pathogens can result in fusarium-like shriveled seeds with white to faint pinkish to orange discoloration. And last, weaker pathogens such as Alternaria and Cladosporium, present in higher intensities, will darken the mycelium along the seed’s crease – another symptom of F. graminearum.
An FDK test looks for typical visual symptoms only, and is a good tool for a very quick analysis of F. graminearum when the pathogen is expected to be present within a given area, or when other pathogen intensities and incidences are also known for the same area. But it’s not the final word by any means – we have used plate and molecular tests on samples with a positive FDK analysis and found that they did not actually contain any F. graminearum. The visual symptoms were caused by other pathogens.
A molecular DNA test is more sensitive and accurate when it comes to identifying the presence of F. graminearum. In a straight-up positive or negative scenario, this test can theoretically detect a single spore on the surface of the seed coat.
The microbiological plate test is another good option. This test surface sterilizes the pathogens on the outside of the seed leaving only seed-borne pathogens, and gives a percent infection rate to an accuracy of +/- 0.5%. At 20/20 Seed Labs, we plate positive DNA tests to get a percent infection so that growers get a complete picture of their seed’s health.
20/20 Seed Labs offers a testing package that includes the DNA testing for F. graminearum, along with the more common pathogens. The Fungal Screen™ package will give you more information about your seed, such as the presence of weaker pathogens, storage molds and other seed-borne diseases.
The best option is always to plant disease free seed, which could be difficult to find after the wet fall of 2010. And with the prediction of another very wet spring in 2011, it is more important than ever to use best practices: seed treatments, proper crop rotation and knowing your seed by testing it properly before you plant it.
Keep an eye on our website for the next article in this series – DON and Mycotoxins: Why they matter to your bottom line. As always, if you have any questions, feel free to contact one of our knowledgeable technician’s at 1-877-420-2099.