Influence of crop volunteer and grassy weed greenbridge on Rhizoctonia root rot of cereals and disease resistance in Brassica and Triticum germplasm

Abstract

Rhizoctonia root rot, caused by Rhizoctonia solani AG 8 and R. oryzae, is considered one of the main deterrents for farmers to adopt reduced tillage systems in the Pacific Northwest. Herbicide application before planting to eliminate weeds is the main management strategy for this disease. To determine the effect of timing of glyphosate applications on the severity of the disease, a 3-year experiment was conducted in a field naturally infested with R. solani and R. oryzae. Weeds were sprayed with glyphosate at 42, 28, 14, 7 and 2 days prior to planting with barley. As the herbicide application to planting interval increased, there were increases in shoot length and healthy roots rating and a decrease in disease severity, number of infected seminal roots and activity of R. solani AG 8.

To investigate the impact of wild oat (Avena fatua L.), Italian ryegrass (Lolium multiflorum), and downy brome ( Bromus tectorum L.) on incidence of the disease, the same three weed species were planted in soil infested with R. solani AG 8 and treated with glyphosate before planting with barley. Significant reductions in shoot length, root length and seedling fresh weight were observed in barley grown in wild oat and Italian ryegrass residue.

Virulence of R. solani AG 2-1, AG 8, AG 10 and Ceratobasidium spp. on Brassica crops were tested. R. solani AG 2-1 appears to be the most aggressive pathogen followed by R. solani AG 8, Ceratobasidium spp. and R. solani AG 10, respectively. Three genotypes with moderate levels of resistance were identified. Regardless of the genotype, old seeds were more susceptible than newly harvested seeds.

The tolerance of 7 synthetic wheat genotypes to R. solani and R. oryzae was studied in two soils. More disease was observed in sandy soil compared to the silty loam soil. R. solani AG 8 was found to be more virulent compared to R. oryzae. Two genotypes with moderate levels of resistance were identified. One QTL for shoot length reduction was located on chromosome 2B in the Louise x SPCB-3104 population. This QTL explained 29% of the phenotypic variation.