Multiple Herbicide Resistance in Wild Oat and Impacts on Physiology, Germinability, and Seed Production

Abstract

Th e evolution of weed biotypes resistant to multiple herbicide modes of action, here termed multiple herbicide resistance, is a growing problem around the world. We investigated two multiple herbicide resistant (MHR) wild oat (Avena fatua L.) populations from Montana and hypothesized that they would exhibit fi tness costs compared with two herbicide-susceptible (HS) populations. Dose-response tests showed that the MHR populations were resistant to difenzoquat (a membrane disruptor), imazamethabenz (an acetolactate synthase [ALS] inhibitor), fl ucarbazone (an ALS inhibitor), and tralkoxydim (an acetyl-CoA carboxylase inhibitor). In greenhouse studies, we assessed diff erences between MHR and HS populations in seed germination, photosynthetic parameters, plant growth, and reproduction. Seeds of one HS population germinated more at cold temperature (4.9°C) and less at high temperature (29.6°C) compared with the other populations. Plants of this HS population also had lower stomatal conductance (23%), intercellular CO 2 concentration (7.5%), and transpiration (15.3%) than the other populations, but there were no diff erences in photosynthetic rates between any populations. Also, there were no diff erences in relative growth rate among all HS and MHR populations. Th e MHR populations initiated seed production several days sooner than the HS populations; however, HS populations produced 67% more tillers, and one HS population ultimately produced 43% more seeds than the MHR populations, indicating a potential fi tness cost of resistance. With the exception of seed production diff erences, our results do not indicate a consistent fi tness cost. More research is needed in fi eld settings and with resource competition to further evaluate fi tness costs in MHR populations.

Intensive herbicide use has selected for constitutively elevated levels of stress‐responsive mRNAs and proteins in multiple herbicide‐resistant Avena fatua L

“…Field‐collected seeds (about 90% of which were resistant to 60 g a.i. ha −1 pinoxaden, data not shown) were subjected to two generations of recurrent group selection (50 plants each generation) by spraying with the same dose of pinoxaden, after which 100% of plants were confirmed to be homozygous resistant to pinoxaden via dose response experiments . From each generation of 50 plants, all seeds were harvested and a random selection of 50 seeds was used to initiate five additional generations without herbicide selection to homogenize the genetic background.…”

“…From each generation of 50 plants, all seeds were harvested and a random selection of 50 seeds was used to initiate five additional generations without herbicide selection to homogenize the genetic background. The HS1 population was derived from seeds collected from untreated border plants in an adjacent field, grown for seven generations as described for MHR4 except without herbicide selection, and was subsequently confirmed to be 100% susceptible to the herbicides used in these studies . A second susceptible population HS2 used for crossing studies (see below) is the highly inbred nondormant SH430 line used in seed dormancy research .…”

“…HR species from the Poaceae family are over‐represented among ‘the world's worst weed families’, and HR A. fatua populations probably have a greater worldwide economic impact than those of any other species . We recently described the MHR3 and MHR4 A. fatua populations from northcentral Montana that are resistant to the acetyl‐CoA carboxylase (ACCase) inhibitors fenoxaprop‐P‐ethyl, tralkoxydim and pinoxaden, the acetolactate synthase (ALS) inhibitors imazamethabenz‐methyl and flucarbazone‐sodium (flucarbazone hereafter), the growth inhibitor difenzoquat, the photosystem I inhibitor paraquat (MHR3 only) and the very long chain fatty acid biosynthesis inhibitor triallate, with resistant/susceptible ED 50 ratios ranging from 1.4 to 57 . Additional herbicide screens show that MHR3 and MHR4 are resistant to US field use rates of quizalofop‐P‐ethyl, fluazifop‐P‐butyl, diclofop‐methyl and prosulfocarb (Dyer et al ., unpublished).…”

Resistance to acetyl‐CoA carboxylase‐inhibiting herbicides

“…The potential fitness cost associated with evolved ACCase‐resistant traits has been examined in seven different weed species (Table ). However, results from some of the studies could not be interpreted adequately, primarily because the mechanism of resistance was not determined and sensitive and resistant populations being compared did not share the same genetic background . Ideally, life history traits, most particularly fecundity, should be assessed in competition under different field conditions using properly characterised and comparable weed lines .…”

The Eco-Evolutionary Imperative: Revisiting Weed Management in the Midst of an Herbicide Resistance Crisis

“…Many of these resistant biotypes also withstand exposure to herbicides from different herbicide families targeting the same site of action, a phenomenon known as cross resistance. Furthermore, the alarming increase in weed biotypes resistant to herbicides targeting different sites of action, referred to as multiple resistance, has created major weed management challenges [39,40]. Concomitant with the loss of efficacy of some herbicides due to resistance, the availability of herbicide chemistries has been declining over the last 25 years due to environmental and human health concerns [41], lack of market and perceived profitability with older post-patent herbicides, and the absence of discovery of novel herbicide chemical families [42].…”