Development of High Levels of Metribuzin Tolerance in Lentil

Abstract

Lentil (Lens culinarisMedik.) is an important and expanding crop in southern Australia and a significant crop in western Canada. Currently, production in both countries is limited by an inability to effectively control weeds, due in part to a lack of registered safe and effective herbicides. Metribuzin is a broad-spectrum herbicide providing an alternative weed control option to the imidazolinones, but it has low crop safety in lentil. Two methods, germplasm screening using a hydroponic sand assay and field screening of a large mutated population of the Australian cultivar ‘PBA Flash’ were initially used to identify lines with putative metribuzin tolerance over current cultivars. Dose–response experiments showed the germplasm line SP1333 had GR50(the rate required to reduce dry weight 50%) values up to four times higher than PBA Flash. However, the mutation selections M043 and M009 had GR50values more than 25 times higher than PBA Flash. A field study in Canada, under conditions of induced shade and no shade 72 h before POST application of metribuzin, confirmed the intermediate level of tolerance in SP1333 and the high level in the two mutant lines compared with 20 Canadian and Australian genotypes. This relative increase in metribuzin tolerance of the two mutant lines over the parent cultivar is higher than all previous reports in a range of crop species. The development of large mutant populations combined with large M2field screens was a successful method for developing high levels of metribuzin tolerance in lentil. The estimated mutation rate of the mutant lines was 9.4×10−8. All three lines are currently being used as parents in lentil breeding programs.

Induced novel psbA mutation (Ala251 to Thr) in higher plants confers resistance to PSII inhibitor metribuzin in Lens culinaris

“…Metribuzin dose response experiments showed GR 50 values were in excess of 11 and 34 times that of the susceptible genotype in M009 and M043, respectively. However, the difference between the two mutants was not significant and supported previous dose response findings, which found similar high levels of resistance (greater than 25 times) compared to PBA Flash in both mutants . Very high metribuzin rates, in excess of 60 times label rates, were required to determine GR 50 values of the mutants in these experiments.…”

“…The GR 50 values for metribuzin in PBA Flash differed twofold between runs but both values were lower than the field label rate of 285 g ha −1 , indicating susceptibility to this herbicide as reported previously. 14 The GR 50 values for metribuzin within each mutant genotype were similar between runs and both exhibited a very high level of resistance when compared to PBA Flash. M009 was 10.4 and 22.1 times greater than PBA Flash across runs one and two, respectively, compared with 32.6 and 55.6 for M043.…”

“…Relatively lower levels of improved resistance to metribuzin were developed in lentil where gamma radiation was used to treat 1000 seeds but the mechanism of resistance was not reported . In comparison, approximately 700 000 lentil seeds were mutagenized with EMS at an estimated M 2 induced mutation rate of 9.4 × 10 −8 to develop the mutants used in this study . Diploid plant cells contain thousands of copies of their chloroplast genome but only two copies of their nuclear genome, which is likely to be a major factor in the lower frequency of observed resistance mutations in the chloroplast psbA gene of the lentils used in this study compared with the nuclear metabolism mechanism found in lupin.…”

“…The EMS mutation induced metribuzin resistant lentil genotypes PBA Flash‐EMS10‐11SVHM043 (M043) and PBA Flash‐EMS10‐11SK‐12PAHM009 (M009) and the susceptible parent cultivar PBA Flash were used in this research . Seeds of all cultivars were produced near Riverton, South Australia during the winter growing season of 2013 and stored dry until required.…”

“…Improved resistance to metribuzin in lentil would allow safe post‐emergent application and a subsequent increase in the effective period of weed control. To address these limitations, two lentil mutants with high levels of resistance to metribuzin, have recently been developed through EMS mutagenesis techniques and field selection . Australian lentil breeding programs are incorporating this resistance into adapted cultivars with the view of developing metribuzin resistant genotypes.…”