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The inheritance of sulfonylurea (SU) resistance in Monochoria vaginalis was investigated based on the bensulfuron-methyl response phenotypes of F1 plants between SU-resistant (R) and -susceptible (S) and segregation analysis in F2 progenies. Differences of SU resistance between SU-R biotypes and F1 plants at the recommended field dose were also investigated by comparing shoot dry weight. All F1 plants survived the treatment with 25 g a.i. ha−1 bensulfuron-methyl, one-third of the recommended field dose, and showed similar responses to SU-R plants. Conversely, all F1 plants died or showed extreme necrosis at 225 g a.i. ha−1, three times the recommended field dose, as SU-S plants. F2 plants were classified as either R or S phenotype. Segregation for resistance to bensulfuron-methyl in F2 families did not differ from the expected 3:1 (R:S) ratio at 25 g a.i. ha−1. At 225 g a.i. ha−1, the F2 families segregated in a 1:3 (R:S) ratio. These results suggest that SU resistance in M. vaginalis is controlled by a single nuclear allele with resistance being dominant at low dose and susceptibility dominant at high dose. Moreover, F1 plants died or were extremely injured after application of bensulfuron-methyl at the recommended field dose, although SU-R biotypes grew normally. [ABSTRACT FROM AUTHOR]

Monochoria vaginalis is one of the most serious weeds of rice fields in Asia. The species is predominantly selfing. To reveal the potential for multiple mutational events, outcrossing and gene flow in the sulfonylurea-resistant (SU-R) M. vaginalis populations, we investigated (i) if each SU-R population was a single SU-R biotype or a mixture of several SU-R biotypes using restriction analysis or direct sequencing of acetolacatate synthase (ALS) genes and (ii) genetic diversity of SU-R and -susceptible (S) populations using amplified fragment length polymorphism (AFLP) analysis. Nineteen or 20 individuals were sampled from four SU-R and five SU-S populations respectively. Amino acid substitutions conferring resistance in the SU-R populations were Pro197Ser in the ALS1 or ALS3, or Asp376Glu in the ALS1 and each SU-R population was composed of a single SU-R biotype. In cluster analysis each SU-R individual formed a cluster, whereas the individuals from a SU-S population belonged to different clusters. Some SU-R populations showed polymorphic AFLP loci. The results indicated that these SU-R biotypes emerged from a single mutational event and any gene flow of SU-R genes from adjacent populations did not occur. A low level of outcrossing and recombinations of SU-R genes occurred within some SU-R populations of M. vaginalis. [ABSTRACT FROM AUTHOR]

Herbicide resistance in Lolium rigidum is widespread across much of the agricultural land in Australia. As the incidence of herbicide resistance has increased, so has the incidence of multiple herbicide resistance. This reduces the herbicide options available for control of this weed. This study reports on the successful amplification and sequencing of the acetolactate synthase (ALS) gene of L. rigidum using primers designed from sequence information of related taxa. This enables, for the first time, the successful determination of a mutation in the ALS gene of this species that provides resistance to ALS-inhibiting herbicides. This mutation causes amino acid substitution at Trp574 (numbering standardised to Arabidopsis thaliana) to Leu which had been reported to confer a high level of resistance against all classes of ALS inhibitor herbicides. In addition, multiple resistance to ALS-inhibiting and acetyl-coenzyme A carboxylase-inhibiting herbicides is acquired through the independent accumulation of mutant alleles for the target sites. This may thus explain some of the irregular, mosaic resistance patterns that occur in this predominantly outcrossing species. [ABSTRACT FROM AUTHOR]