Sudden Death Syndrome (SDS) caused by Fusarium virguliforme (Fv) is currently the most damaging fungal soybean disease occurring in Minnesota. Soybean diseases are controlled most effectively and economically by breeding for disease resistance. No soybean genotype is completely resistant to SDS; instead the reaction of soybean to this disease is characterized as partial resistance involving multiple genes. New molecular techniques, particularly association mapping, make identification of multiple resistance genes feasible if quality disease phenotype data is available. Selection for this type of resistance is made complex by the fact that varietal resistance to SDS functions both in the root to limit infection and in the leaves to limit expression of foliar symptoms. The relative value of root vs foliar resistance is poorly understood. Evaluation of multiple resistance traits yielding quality resistance data for many cultivars is dependent on achieving consistent and repeatable root infection and foliar symptom expression. We have characterized soybean varieties from the University of Minnesota Breeding Program that are uniquely resistant to either root infection or foliar symptom development and seek to determine the relative contribution of each form of resistance to final yield. In previous experiments we investigated inoculant and environmental conditions contributing to measurable SDS infection. To support or research into infection requirements we intend to refine a set of environmental requirements necessary to achieve consistent infection by inoculation in order to promote SDS symptom development.

Objective 1: To determine the relative importance of resistance to root infection compared with resistance to foliar symptom exp
Determine the effectiveness of root rot or foliar symptom resistance with increasing inoculum density.
Characterize the yield response of soybean varieties expressing either resistance as resistance to root rot 30 days after planting or resistance to foliar symptom expression during early vegetative growth stages and during late reproductive development.
Objective 2: To characterize experimental requirements, light intensity and growth media, that facilitate repeatable disease ass
Identify inoculum substrates that consistently support SDS infection and symptom development.
Determine light intensity necessary for the development of foliar symptoms in controlled environments, greenhouse or growth chamber.
Objective 3: To identify markers that less susceptible to the effect of environmental conditions. The goal of this objective is
Identify objective, quantifiable proxy markers for plant resistance such as biochemical, hyperspectral reflectance, or molecular markers, that enable rapid phenotyping of the response of soybean varieties to Fv infection.
Determine if symptoms evaluated with proxy methods such as hyperspectral reflectance, fungal DNA concentration, or toxin concentration correlate with results obtained by visual assessment or physical measurement.

Updated May 28, 2020:

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