From many of the samples we recovered both Pythium spp. and Fusarium spp.. Both are well-known seedling pathogens. Our next step was to examine what the Pythium spp. were and then to determine if these were sensitive to metalaxyl. In approximately 60% of the locations we were able to obtain a good quality sequence and a metalaxyl test for 28 isolates.
From many of the samples we recovered both Pythium spp. and Fusarium spp.. Both are well-known seedling pathogens. Our next step was to examine what the Pythium spp. were and then to determine if these were sensitive to metalaxyl. In approximately 60% of the locations we were able to obtain a good quality sequence and a metalaxyl test for 28 isolates.
We found a great diversity of Pythium spp., all have been reported previously as pathogens of soybean or corn. Many have been found in Ohio in previous surveys. The bottom line is that it was not the same one in each field, and where we were able to recover more than one isolate from a field – they were different species. Again, this confirms our earlier reports that this is a very diverse group of pathogens in Ohio that are capable of causing widespread stand loss.
Table 1. Summary of Pythium spp. recovered from symptomatic soybean seedlings collected in Ohio during the spring of 2014.
|
Pythium spp. |
Number of locations |
Insensitive to metalaxyl |
Sensitive to metalaxyl |
|
conidiophorum |
1 |
1 |
0 |
|
dissotocum |
3 |
3 |
0 |
|
heterothallicum |
1 |
1 |
0 |
|
inflatum |
1 |
1 |
0 |
|
perplexum |
3 |
3 |
0 |
|
sylvaticum |
3 |
2 |
1* |
|
torulosum |
3 |
3 |
0 |
|
ultimum var ultimum |
2 |
1 |
1 |
|
vexans |
1 |
1 |
0 |
|
|
|
|
|
*2 isolates from one location, one grew at 100 ppm, the other no.
Conclusion. Clearly the seed treatments did not hold up in this scenario. Seed treatments with only one active ingredient for Pythium spp. will not provide protection for the wide range of diversity that is now contributing to this disease complex.
For the 2015 season, for those fields with a history of replant and stand establishment issues should focus on seed treatment that has a wide combination of active ingredients.
Other contributing others included: Clifton Martin, Chrissy Balk, and Damitha Wickramasinghe