Improved Understanding of Mitotic-Inhibiting Herbicide Resistance in Poa annua and Eleusine indica

Abstract

Poa annua is a problematic weed that infests golf courses, sports fields, and home lawns. Mitotic-inhibiting herbicides are often used to control Poa annua in these affected areas. However, resistance to mitotic-inhibiting herbicides has developed due to unaltered herbicide regimes. Suspected resistant populations were collected from across the state of Alabama and screened for resistance to prodiamine. Populations were then sequenced for known target-site mutations located on the alpha-tubulin gene. The mutation Thr239-Ile on the alpha-tubulin gene was discovered in each of the three suspected resistant populations tested. The results from this study indicated that these mutations confer resistance to prodiamine and cross-resistance to dithiopyr. The level of resistance to prodiamine for the R populations were 1.6, 16.5, and 4.6 times more than the susceptible population based on seedling emergence response and 1.8, 59.2, and 1.4 times more than the susceptible population based on biomass reduction response. The level of resistance to dithiopyr for the R populations were 4.6, 5.0, and 6.8 times more than the susceptible population based on seedling emergence response and 3.9, 9.1, and 11.2 times more than the susceptible population based on biomass reduction response. Goosegrass (Eleusine indica) is a summer annual grass that is a problematic weed in turfgrass. Dithiopyr and dinitroanilines are mitotic-inhibiting herbicides that are commonly used as a preemergent application to control goosegrass. A suspected resistant goosegrass population was collected from a golf course putting green and was evaluated for possible resistance to dithiopyr and prodiamine. After rate response evaluation, the alpha-tubulin gene was sequenced for known target-site mutations that have been reported to confer resistance to mitotic-inhibiting herbicides. A mutation was discovered that resulted in an amino acid substitution at position 136 from leucine to phenylalanine (Leu136-Phe). Previous research has indicated that Leu136-Phe does confer resistance to dinitroaniline herbicides. The level of resistance indicated by regression models and I50 values indicates that there is a 54.1-, 4.7-, >100-, and >100-fold resistance to dithiopyr, prodiamine, pendimethalin, and oryzalin, respectively when compared to the susceptible population based on seedling emergence response and 88.4-, 7.8-, >100-, and >100-fold resistance to dithiopyr, prodiamine, pendimethalin, and oryzalin, respectively when compared to the susceptible population based on biomass reduction response.