Evaluation of fungal root diseases in soybean fields in Montérégie region in 2014 and 2015
A survey on soybean root diseases caused by fungi and oomycetes was conducted in 2014 and 2015 in 80 fields in Montérégie and 4 fields in Centre-du-Québec. Twelve seedlings at two-trifoliate-leaf stage were collected per field to assess their root health (root index) on a scale of 1 to 5 (1 = healthy abundant roots, 5 = necrosis and few roots), and to reveal in theses roots, by plating techniques, the presence of pathogenic fungi and oomycetes. The average root index for all fields was 2.6 in 2014 and 3.2 in 2015. Pythium and Fusarium species were present in almost 100% of the fields each year, while Rhizoctonia solani and Thielaviopsis basicola were more abundant in 2015 (88% of the fields) than in 2014 (52%). Phytophthora sojae was not isolated from any root, but was isolated from soils in 37% of the fields. The most common Fusarium species were F. solani, F. oxysporum and F. equiseti, found in at least 60% of the fields. The stepwise-analysis method selected three factors to explain the variation of root index, two of which showed significant differences between their levels, namely the type of seeds (higher index for non-GMOs than for GMOs). and the number of years in soybean crop over the past four years (index increasing with the number of years). Tillage was the only factor selected to explain the variation of the sum of Fusarium isolates (sum decreasing with the intensity of tillage).