2012 Annual Report
1a.Objectives (from AD-416):
Survey wheat growing areas of the United States for Rhizoctonia groups and species infecting cereals (wheat and barley) and rotation crops.
1b.Approach (from AD-416):
Soil samples will be sent to Pullman by Syngenta staff and other University and ARS cooperators. Rhizoctonia will be isolated from the soils, cultured, and identified using sequencing of the ITS region. Representatives isolates will be tested in greenhouse for pathogenicity.
Root diseases, including take-all, Pythium, Rhizoctonia and common root rots, and Fusarium crown rot, cause $3.5 billion in losses annually to U.S. wheat and barley growers. For most of these diseases, there are no resistant varieties and chemical treatments are not available or perform inconsistently. Modern production practices of reduced tillage and direct seeding, used to control soil erosion, exacerbates the incidence and severity of root diseases. Over the last 25 years, a large amount of research on Rhizoctonia groups and species has been conducted in the inland Pacific Northwest, but little is known about Rhizoctonia in other wheat growing areas of the United States. ARS scientists at Pullman, Washington, in collaboration with scientists at Syngenta surveyed all major cereal growing areas in the U.S. for Rhizoctonia species. Using their network of field and sales reps, Syngenta collected soil samples from all of these areas and shipping them to Pullman. As of May 2012, over 160 samples were analyzed, and 79 different isolates were identified from 51 locations. The most predominant anastomosis group (AG) and species in U.S. wheat fields were Rhizoctonia oryzae and R. solani AG 2-1. Surprisingly, AG-8, the causal agent of classic Rhizoctonia root rot and bare patch, was not found outside of the Pacific Northwest. As many as four different AGs or species of Rhizoctonia occurred in a given soil sample. Pathogenicity testing in the greenhouse showed that AG-8 was the most virulent on wheat and barley, but AG 2-1, 3, and 4 could also cause reductions in height and plant biomass. This study was the first national survey of Rhizoctonia on small grains and is greatly increasing the capacity of ARS and Syngenta to respond to outbreaks of this important root pathogen. Accomplishments align with Component 2, Problem Statement 2C of NP 303.