Protocols for Robust Herbicide Resistance Testing in Different Weed Species

Abstract

Robust protocols to test putative herbicide resistant weed populations at whole plant level are essential to confirm the resistance status. The presented protocols, based on whole-plant bioassays performed in a greenhouse, can be readily adapted to a wide range of weed species and herbicides through appropriate variants. Seed samples from plants that survived a field herbicide treatment are collected and stored dry at low temperature until used. Germination methods differ according to weed species and seed dormancy type. Seedlings at similar growth stage are transplanted and maintained in the greenhouse under appropriate conditions until plants have reached the right growth stage for herbicide treatment. Accuracy is required to prepare the herbicide solution to avoid unverifiable mistakes. Other critical steps such as the application volume and spray speed are also evaluated. The advantages of this protocol, compared to others based on whole plant bioassays using one herbicide dose, are related to the higher reliability and the possibility of inferring the resistance level. Quicker and less expensive in vivo or in vitro diagnostic screening tests have been proposed (Petri dish bioassays, spectrophotometric tests), but they provide only qualitative information and their widespread use is hindered by the laborious set-up that some species may require. For routine resistance testing, the proposed whole plant bioassay can be applied at only one herbicide dose, so reducing the costs. Video LinkThe video component of this article can be found at

A family affair: resistance mechanism and alternative control of three Amaranthus species resistant to acetolactate synthase inhibitors in Italy

“…Seed germination procedure was the same as in Section 3.2 . Seedlings growth and herbicide treatment were done following an established protocol . Experimental layout was a complete randomized design with two replicates (trays).…”

“…30 Seedlings growth and herbicide treatment were done following an established protocol. 42 Experimental layout was a complete randomized design with two replicates (trays). Twenty seedlings per population, at similar growth stage, were transplanted into plastic trays (325 × 265 × 95 mm) with a standard potting mix (60% silty loam soil, 15% sand, 15% perlite and 10% peat) and watered daily as required.…”

Epidemiology and agronomic predictors of herbicide resistance in rice at a large scale

“…Since 1997, the Italian Herbicide Resistance Working Group (GIRE, www.resistenzaerbicidi.it) has been monitoring, collecting, and testing putative herbicide-resistant populations nationwide, based on farmers and farmers' advisor complaints of poor herbicide efficacy. All other available data on herbicide resistance in Italy were also collected, and all populations that were confirmed resistant to at least one herbicide through a standardized testing procedure (Panozzo et al 2015a) were included in a national herbicide resistance database. The part of the database relative to the populations collected in the main rice producing area in Italy (approximately 200,000 ha, i.e., about 85% of the total rice growing area) was used as input to produce maps of herbicide resistance diffusion using iMAR application (Panozzo et al 2015b;GIRE 2018).…”

“…All seed samples were cleaned and dry stored at room temperature. Two whole-plant herbicide sensitivity experiments were then performed in greenhouse conditions following a standardized testing procedure (Panozzo et al 2015a), in autumn 2016 (A) and a repetition in spring 2017 (S).…”

“…Populations were then divided into four categories: S when less than 5% of plants survived the 1× dose, SR when survival at 1× dose ranged between 5 and 20%, R when survival at 1× was > 20%, and RR when > 10% of plants survived the 3× dose and > 20% the recommended field dose (Panozzo et al 2015a). To test whether the two experiments could be pooled, Levene's test was performed: as both survival and fresh weight variances proved to be homogeneous (p = 0.22 and p = 0.74), data from the two experiments were pooled and analyzed together.…”