First report of Rhizoctonia solani AG-4 HGII causing root rot and damping-off on quinoa ( Chenopodium quinoa ) in Canada

In June 2022, quinoa (Chenopodium quinoa) plants exhibiting symptoms of root rot and seedling damping-off were observed in two commercial fields in Saskatchewan, Canada. Disease incidence was recorded in 14% and 11% of plants in the respective fields. Three fungal isolates were obtained from diseased seedlings and their morphological characteristics were consistent with those of Rhizoctonia solani. The isolates were identified as R. solani AG-4 HGII based on anastomosis groupings and subgroup-specific primers. nBlast and phylogenetic analysis of rDNA-ITS sequences confirmed that the isolates (GenBank accession nos. PQ152665, PQ867861 and PQ867862) grouped within the same clade as previously identified R. solani AG-4 HGII sequences. Pathogenicity tests were conducted by inoculating 2-week-old quinoa seedlings with mycelial plugs. After 10 days, inoculated seedlings developed seedling damping-off symptoms with reddish-brown stem necrosis near the soil surface and sunken brown root lesions, while control plants remained asymptomatic. Koch’s postulates were fulfilled through the consistent re-isolation of R. solani AG-4 HGII, confirming it as the causal agent of quinoa seedling root rot. To our knowledge, this is the first report of R. solani AG-4 HGII causing disease on quinoa in the field.