Assessment of weedy rice sensitivity to imazamox with a fast dose-response bioassay

The objective of this work was to evaluate a low-cost, quick dose-response assay for the assessment of imazamox sensitivity in Italian weedy rice populations. Seeds of ten weedy rice populations and five cultivars (four of which tolerant to imidazolinones herbicides) were incubated in filter paper saturated with distilled water in the light at 25°C for five days. After this time, the seedlings reached the two- to three- leaf stage. The seminal roots of the seedlings were then cut and the seedlings were placed in 50mL-plastic glasses containing 20mL of vermiculite and 30mL of a solution with a specific dose of imazamox. The tested concentrations were 0.01mM, 0.1mM, 1mM, 10mM, 100mM, 1M and 4M. Assessment of plant response to herbicide treatments was carried out after six days by measuring length of the newly formed roots. Data were fitted to a 4-parameter log-logistic model and comparisons between populations were made using estimated imazamox concentrations able to affect root length by 50% (IC50). On this base, imazamox sensitivity of weedy rice populations varied between about 102 and 109 times that of the average sensitivity of imazamox-tolerant rice cultivar. The discriminatory concentrations for weedy rice, conventional rice and imazamox-tolerant rice plants were <0.0001M, <0.0001M and >0.01M, respectively. This screening technique was proved to be a fast and low-cost tool for preliminary determination weedy rice sensitivity to imazamox.