Research Objective
To survey on the occurrence of Fusarium, Rhizoctonia and Pythium fungal spp. and the soybean cyst nematode in Western and Eastern Canada; to monitor the spread of sudden death syndrome (SDS) in Ontario and establish a nursery to screen for tolerance; to utilize advanced PCR analysis of root rot pathogens (e.g., droplet digital PCR), which enable highly precise quantification of target DNA; to identify new/emerging root rot pathogens (e.g., Fusarium proliferatum) and determine the impact of F. proliferatum on soybean yield.
To achieve these objectives, a comprehensive approach was taken. This included a series of greenhouse trials, field trials, and lab studies. These studies were conducted on plant samples from various regions across Canada and tested for the presence and severity of root rot pathogens. The aim was to better understand and implement tolerance and resistance to root rots. Soil samples were also collected for Soybean Cyst Nematode (SCN) research purposes. Research for this project occurred between 2018 and 2023.
Objective 1
A national survey including soybean root samples from across Saskatchewan, Manitoba, Ontario, and Quebec in 2022 found root rot in 100% of samples collected, most frequently caused by Fusarium spp. pathogens. These findings underscore the urgent need for effective management strategies. In 2022, average root rot severity ratings indicative of at least half of the plant’s root system being affected, leading to detrimental yield effects, were 56%, 15%, 70%, and 100% in Saskatchewan, Manitoba, Ontario, and Quebec respectively. These ratings are lower than those from 2021 in all cases, except for Quebec, which had no data for 2021. Neither Rhizoctonia root rot nor Pythium root rot was found in any of the 2022 root samples. Samples continue to be tested for additional root rot-causing pathogens, including Pythium spp., additional Fusarium spp., and R. solani, using molecular detection methods.
During the sampling in Ontario, soil samples were collected for SCN counts. The analysis revealed that 98% of these soil samples had detectable SCN levels, with most samples able to reproduce on currently available resistant cultivars. However, no field samples from outside of Ontario were found to have quantifiable SCN levels, indicating a slow expansion of SCN into new soybean planting areas. This ongoing monitoring of SCN expansion underscores our commitment to staying ahead of potential threats and ensuring the continued health of soybean crops.
Objective 2
In terms of Sudden Death Syndrome (SDS) research, an in-field disease nursery was established near Chatham, Ont. in 2018. The nursery was inoculated with Fusarium virguliforme, the pathogen responsible for SDS, to be used for variety screening of cultivars of varying SDS susceptibility. This variety screening for SDS was effectively performed on over 90 soybean lines at three sites in 2021 and 2022, and disease surveys on an additional 73 farms in 2022 in Ontario provided practical insights for soybean farmers.
SDS continues to be highly damaging in the southernmost point in Ontario, previously identified as a region of high SDS pressure. Some geographical expansion is noted towards the east and moving northwards. Moisture timing appears to be a causal agent in the spread and damage levels caused by SDS more so than total moisture over the growing season.
Objective 3
Resistance screening techniques were improved through droplet digital PCR (ddPCR), a new next-generation PCR technology for detecting and quantifying pathogens. Primer and probe sets have been validated and optimized for the detection of multiple Fusarium spp. as well as Rhizoctonia solani in soybean root and soil samples. Soybean root DNA extractions have been completed on over 500 samples from 2018 to 2021 and are in progress for 2022 samples. Using ddPCR, these samples will be tested for absolute quantification of root pathogens in the near future.
This research will contribute to the more precise and rapid identification and quantification of root rot pathogens through the development of superior molecular diagnostic tools. This will lead to better-informed risk management and improved outcomes for farmers.
Objective 4
In 2018, greenhouse and field trials were conducted in Alberta on two susceptible soybean cultivars inoculated with F. proliferatum, a pathogen that causes soybean root rot. Plants were assessed for root rot three weeks after planting in the controlled environment and four weeks after planting in the field trials.
Additional studies researched the pathogenicity of over 100 Fusarium spp. isolates on soybeans in southern Alberta, finding ten pathogenic, with F. acuminatum being the most prevalent. Three species – Fusarium commune, F. redolens and F. torulosum – were also identified as new root pathogens of soybeans.