Fungicide seed treatments reduce root rot of soybean

All of the fungicides and fungicide mixtures tested in field experiments reduced root rot in Fusarium infected soybean seedlings. Varieties were identified that could be used in plant breeding programs to develop Fusarium-resistant varieties.

The potential for growing soybean in southern Alberta has increased with the availability of early maturing soybean varieties. However, root rot is a serious disease and recent field surveys in southern Alberta have detected high incidence and severity in commercial soybean crops.

In Alberta, Fusarium proliferatrum, F. avenaceum and F. acuminatum are the main pathogens causing root rot in soybean. Infection by Fusarium species can cause seedling mortality in soybeans and reduce root mass in infected soybean plants at all stages of development, resulting in decreased water and nutrient uptake and lower yields.

Research was conducted at the Crop Diversification Centre South, Brooks, Alberta to compare the efficacy of fungicide seed treatments in reducing Fusarium root rot of soybeans, promoting seedling survival and maintaining yield. A collection of short-season soybean varieties was evaluated for their responses to Fusarium root rot disease.

Fungicide seed treatments

In both field trials and greenhouse experiments, the efficacy of nine seed-treatment fungicides was evaluated on the soybean cultivar ‘TH29002RR’. The trials included both a Fusarium inoculated (F. avenaceum) control and a non-inoculated control for comparison. An assessment of seedling emergence was conducted four weeks after planting, while root rot severity and nodulation were evaluated at the R3 or early pod development stage of plant growth. The field plots were harvested at maturity and yield response assessed.

Source: Hwang et al. 2019

The results from the field experiments showed that all of the fungicides and fungicide mixtures evaluated reduced root rot in the Fusarium inoculated soybean seedlings compared to the control. The same reductions were found under greenhouse conditions, with the exception of Vibrance + Apron XL. Under field conditions, the seed yield for the non-inoculated control was highest compared to the treated plots. Only the treatment with Rancona Summit + Apron XL or Apron Maxx RTA resulted in a higher seed yield compared with the inoculated control, while none of the other seed treatments produced a significantly different seed yield.

Overall, the study showed that fungicide seed treatments can help mitigate the risk to soybean crops caused by Fusarium spp.

Soybean root rot resistance

Under field conditions, 10 short-season glyphosate-tolerant soybean varieties were compared for resistance or tolerance to Fusarium root rot. In addition, 2 glyphosate-sensitive varieties were added to the evaluation under greenhouse conditions. The replicated experiments included a comparison of all varieties and a control of both Fusarium inoculated (F. avenaceum) plots and non-inoculated plots. An assessment of soybean root rot severity, nodulation, seedling emergence, and yield were analyzed, using the same methods as the fungicide experiments.

Overall, the field trials showed that none of the soybean varieties exhibited complete immunity to Fusarium root rot. However, researchers observed various levels of partial genetic resistance among the 10 varieties in the field experiments and the 12 under greenhouse conditions. There were also genetic differences in seed yield losses among the soybean varieties, although these variations could not always be directly correlated with root rot scores or with seedling emergence.

Based on the results, the varieties with the highest Fusarium root rot resistance levels should be investigated to enable plant breeders to design breeding strategies to upregulate the resistance genes or their mechanisms and possibly produce varieties that are totally resistant to root rot.

This research was funded by the Government of Canada through the Agri-Flex Program, Growing Forward 2, and Pest Management and Surveillance Implementation (Pulse Cluster of Agriculture and Agri-Food Canada), and by the Saskatchewan Pulse Growers and Manitoba Pulse Growers Associations.

R. Nyandoro, K.F. Chang, S.F. Hwang, H.U. Ahmed, G.D. Turnbull, and S.E. Strelkov (2019). Management of root rot of soybean in Alberta with fungicide seed treatments and genetic resistance. Canadian Journal of Plant Science 99:499-509




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