Field assessment of microbial inoculants to control Rhizoctonia root rot on wheat.

Graphical abstract Highlights • Seed applied microbes assessed for Rhizoctonia root rot control in field. • An alternate row microplot system developed for initial field assessment. • Effective strains then tested in 20 m split-plots for disease control and yield. • Paenibacillus S4 and Streptomyces F5 were equal or better than chemical controls. • Best performing strain reduced root disease 30% and increased yield up to 4.2%. Abstract Rhizoctonia root rot caused by Rhizoctonia solani AG8 is a major disease in dryland cereal crops. Previous research identified a suite of microbes using in planta bioassay screening that are effective as seed-coated inoculants for control of Rhizoctonia root rot on wheat. This paper assessed 23 strains in fields in Australia with a history of naturally occurring R. solani AG8. Due to the patchy nature of Rhizoctonia root rot in the field, a 2-phase split-plot field trial system was used to allow comparison for disease control efficacy in the same disease space. Seed applied strains were first assessed for their ability to reduce Rhizoctonia using 'microplots' which compare adjacent treated and untreated one metre rows. Up to 10% increases in plant growth and a 32% reduction in root disease was measured at eight weeks after sowing. Selected strains were then assessed in 20 m six row (3 + 3) split plots for their effects on early season wheat growth and root damage and for grain yield. A Paenibacillus and a Streptomyces strain were identified which were able to reduce root damage by 20% and 32% and increase grain yield by 4.2% and 2.8%, respectively, compared to untreated controls. The current best registered chemical control for Rhizoctonia root rot reduced root disease by 35% and increased yield by 3.0% in the same trial. [ABSTRACT FROM AUTHOR]