Search

Management of perennial weeds has become increasingly complex with the reduction of herbicide use and tillage. Their capacity to store nutrients into vegetative organs and to regenerate to establish new individuals makes them very persistent and hard to control. A key aspect for managing perennial weeds is to minimise storage reserves to reduce vegetative regeneration. For that prospect, better knowledge of the regrowth capacities from storage organs is needed. Our work focused on the mechanistic understanding of belowground regrowth dynamics from fragments of Elymus repens rhizomes by analysing the effect of source and sink factors. The effect of rhizome fragment weight (i.e., source) and the number of regrowing buds and belowground shoots (i.e., sinks) was assessed for four mechanisms: sprouting, belowground shoot elongation, belowground shoot biomass to length conversion and biomass allocation to belowground shoots versus roots. Heavier fragments contributed to faster sprouting, faster belowground shoot elongation and increased the proportion of remobilised biomass allocated to belowground shoots. Higher belowground shoot density increased the proportion of remobilised biomass allocated to belowground shoots but decreased individual elongation rate. In other words, larger reserves resulted in a better regeneration capacity and a higher number of growing belowground shoots increased the competition for reserves among them. The belowground shoot that sprouted first on a fragment grew faster and dominated the other shoots on the same fragment. Dominant belowground shoots were located toward the apical end of the fragment. These findings support the fact that tillage should aim at cutting storage organs into the smallest fragments possible to reduce regeneration capacity. This study also emphasised that belowground regrowth mechanisms are complex, and further studies should investigate other species with different types of storage organs. [ABSTRACT FROM AUTHOR]

The ecological consequences of seed size variation have been studied extensively in plants. Curiously, little attention has been paid to the qualitative and quantitative variation of the seed-stored molecules and on their ecological significance. Here, we analysed the oil content and oil composition of ca. 200 weed seed species from agricultural fields in France based on single seed accessions, concentrating on interspecies differences and ignoring within-species variation. The relationships between seed weight, oil %, fatty acids ( FAs) and the energetic value of the seed and its antioxidant properties were also investigated. The antioxidant activity could contribute to protect the oily seed reserves from alteration over time. Among the species analysed, we found a considerable quantitative (oil%) and qualitative variation of FAs stored in the seeds. Such variation was largely related to the plant family of the different species, but intrafamily variation was also found. Heavier seeds contained less oil on a per gram basis than lighter seeds, suggesting a trade-off between seed weight and oil ratio in the seed and that oil storage strategy depends on seed size. Moreover, oily seeds contained more polyunsaturated FAs. However, contrary to our hypothesis, we did not found a higher antioxidant capability in oily seed extracts than in non-oily seeds, nor to the quantitative or to the qualitative variation of FAs in the seeds. Considering the role of these important trait variations on weed ecological strategies, such as germination period, seed predation rate and competition-colonisation trade-off, could improve the sustainable management of weed communities. [ABSTRACT FROM AUTHOR]

RouxF, MatejicekA&ReboudX (2005) Response ofArabidopsis thalianato 22 ALS inhibitors: baseline toxicity and cross-resistance ofcsr1-1andcsr1-2resistant mutants.Weed Research45, 220–227.The baseline toxicity of 22 acetolactate synthase (ALS)-inhibiting herbicides and the cross-resistance patterns of chlorsulfuron- and imazapyr-resistant (R) lines on these 22 ALS-inhibiting herbicides were investigated using the model speciesArabidopsis thaliana. The 22 herbicides consisted of 18 sulfonylureas (SU), three imidazolinones (IMI) and one triazolopyrimidine (TP). The ED50 values (doses of herbicides required to reduce dry matter by 50%) of the post-emergence-treated Col and Ler susceptible (S) lines ranged from 22 to 4822 mg ha−1 and from 17 to 3143 mg ha−1 respectively. Thecsr1-1chlorsulfuron-resistant line (substitution of Pro197 to Ser) conferred a high resistance to the only TP tested as well as to nine SU herbicides (R:Sratio≥30), a low resistance to two SU herbicides (R:S≥5 and<30) and little or no resistance to the three IMI and seven other SU herbicides (R:S<5). This result contradicts the expectation that an ALS mutation selected by an SU herbicide confers high cross-resistance to other SU herbicides. We found that the efficacy of specific ALS inhibitors was different for different species and therefore could not be predicted from our results withA. thaliana; however, the cross-resistance patterns inA. thalianawere highly correlated with cross-resistance patterns in unrelated species with the same resistance mutation. These results have implications for resistance management. [ABSTRACT FROM AUTHOR]