Growth behavior and glyphosate resistance level in 10 biotypes of Echinochloa colona in Australia

Abstract

Recently, poor control of Echinochloa colona with glyphosate has been reported in no-till agriculture systems of the northern grain region (NGR) of Australia. Two experiments were conducted using 10 biotypes of E. colona selected from the NGR of Australia to understand differences in their growth behavior and resistance pattern. Growth studies revealed that these biotypes differed in plant height (53-70 cm plant-1), tiller production (30-52 tillers plant-1), leaf production (124-186 leaves plant-1) and seed head production (37-65 seed heads plant-1). Days taken to seed heads and shoot biomass in these biotypes ranged between 40-48 d and 21-27 g plant-1, respectively. Seed production in these biotypes ranged between 5380 and 10244 seeds plant-1; lowest for biotype B17/25 and highest for biotype B17/13. Correlation studies revealed that seed number plant-1 had a positive correlation with plant height (r = 0.67), tiller number plant-1 (r = 0.89), leaf number plant-1 (r = 0.73), seed heads plant-1 (r = 0.78), seed head weight (r = 0.79), shoot biomass (r = 0.77) and root biomass (r = 0.46). The glyphosate dose-response study showed a wide range of responses in these biotypes and the glyphosate dose required to reduce 50% biomass (GR50 values) was estimated between 217 to 2159 g a.e. glyphosate ha-1. GR50 values of biotypes B17/16, B 17/34 and B17/35 were 719, 2159 and 884 g ha-1, respectively, making them 3, 10 and 4-fold resistant to glyphosate compared with the susceptible biotype B17/37. Growth behavior and seed production potential in these biotypes had no correlation with the resistance index. These results suggest that some biotypes of E. colona are highly problematic; for example, biotype B17/34 was not only highly glyphosate-resistant, but also produced a high seed number (9300 seeds plant-1). This study demonstrated that there is a possibility of great risk with the increased use of glyphosate for managing E. colona in the NGR of Australia. The results warrant integrated weed management strategies and improved stewardship guidelines are required for managing glyphosate-resistant biotypes of E. colona and to restrict further movement of resistant biotypes to other regions of Australia.