Poster Session: Phylloplane and Rhizosphere Ecology

513-P

Flooding duration affects severity of soybean sudden death syndrome.
N. ABDELSAMAD (1), L. F. Leandro (1)
(1) Iowa State University, Ames, IA, U.S.A.

It is well known that high soil moisture and irrigation favor sudden death syndrome (SDS), but the effect of flooding on disease severity is not clear. Greenhouse studies were conducted to test the effect of flooding duration on SDS caused by Fusarium virguliforme (Fv). Soybean cultivar Williams 82 (susc.) and MN1606 (resist) were grown in infested soil until VC stage. Non-infested soil was used for controls. Plants were then exposed to different periods of flooding by maintaining water level one inch above the soil surface for 0, 3, 5, 7 days, and in repeated short-term (RS) applications of 8h/week for 3 weeks. Root rot and foliar severity, root dry weight, and Fv inoculum density in soil were assessed 7, 14, and 21 days after flooding (DAF). Twenty-one DAF, seedlings in the 0-day, 3-day and RS flooding treatments showed the highest root rot and foliar symptom severity and the 7-day flooding treatment showed the lowest severity (P<0.05). Fusarium virguliforme inoculum density in soil was lower (P<0.0001) in 7-day compared to 0-day and RS flooding treatments. Similar results were found for root rot, foliar symptom severity, and Fv inoculum density 7 and 14 DAF. Root dry weight of infested seedlings did not differ among treatments, but in non-infested seedlings, the 0-day and RS flooding treatments showed the highest dry weight 7 and 14 DAF. These results suggest that prolonged flooding (5 and 7 days) has a negative impact on Fv infection and population in soil.