Evolution of ACCase-ALS multiple resistant Lolium from an ACCase resistant population (Abstract/Comunicazione in atti di convegno)

  • Evolution of ACCase-ALS multiple resistant Lolium from an ACCase resistant population (Abstract/Comunicazione in atti di convegno) (literal)
  • 2011-01-01T00:00:00+01:00 (literal)
Alternative label
  • Collavo A., Tracchi G., Guerra G., Sattin M. (2011)
    Evolution of ACCase-ALS multiple resistant Lolium from an ACCase resistant population
    in International Conference "Resistance 2011", Harpenden, 5-7 settembre 2011
  • Collavo A., Tracchi G., Guerra G., Sattin M. (literal)
  • Comunicazione (literal)
  • IBAF-CNR Bayer Cropscince (literal)
  • Evolution of ACCase-ALS multiple resistant Lolium from an ACCase resistant population (literal)
  • Herbicide resistant individuals naturally occur in weed populations but at a low frequency: the higher the weed infestation, the higher is the risk of selecting those individuals. The evolution of the relative abundance of resistant and susceptible plants is driven by the intensity of selection pressure. Some modes of action (MoA), like ACCase and ALS inhibitors, are more prone than others to select resistant individuals within a population. Resistance generally occurs in cropping systems characterised by low diversity in space and time, high selection pressure and no or reduced rotation of herbicide MoA. This is often the case of durum wheat cultivated in central and southern Italy where ACCase resistance is frequent in several areas. The first cases of ACCase resistant populations appeared in the mid-'90s, while the first populations with multiple resistance to ACCase and ALS inhibitors were found around 2005, after the introduction of graminicide sulfonylureas in 2001. So far, there are no Lolium populations resistant only to ALS inhibitors. Very little information is available on the long-term effects of alternating ACCase and ALS inhibitors on the possible evolution of multiple resistance. In this study different weed management strategies were tested in a long-term field experiment cultivated with durum wheat. Initially, the area was heavily infested by Lolium spp. cross-resistant to most ACCase inhibitors. Four weed control strategies were compared over seven years: 1) continuous use of ACCase inhibitors; 2) continuous use of ALS inhibitors; 3) alternation between ALS and other MoA; 4) untreated check. Efficacy of treatments and crop yield were monitored in the field, while seeds were sampled from Lolium survivors in all plots during the seven years and then used for greenhouse and outdoor pot experiments to test ACCase and ALS inhibitors efficacy through plant survival and visual estimation of the biomass. As expected, optimal control was achieved during the first three years in both the alternating strategy and continuous application of ALS inhibitors. The sulfonylureas efficacy steadily declined from the fourth year onwards in the continuous treatment, while it stabilised at around 80% in the rotated treatment. It is important to note that, regardless of the control strategy, very few survivors were observed after the second treatment with sulfonylureas. Results from the bioassays indicate that, regardless of the control strategy, the few survivors of the third ALS treatment produced a significant number of multiple resistant progeny. The efficacy of the fourth sulfonylurea treatment generally dropped to around 80%. A few ALS-resistant individuals were also found in those plots not treated with sulfonylureas, this is likely due to pollen flow. At the end of the experiment, multiple resistant individuals were found in all samples coming from the four control strategies. The continuous use of ALS inhibitors led to a fast selection of multiple resistant plants. Even the simple alternation between ALS and other MoA was revealed to be a short-term solution. However, the field efficacy of sulfonylureas remained relatively high until the end of the experiment. Significantly lower infestation was observed where there was alternation of MoA. Resistance management strategies should introduce more diversity into the system, e.g. pre-emergence treatments, and including forms of non-chemical control and alternation between summer and winter crops. (literal)
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