Ecological and genetic characteristics of sulfonylurea-resistant Monochoria vagina us, a paddy weed

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Sulfonylurea (SU) herbicide is the most important herbicide used in paddy fields in Japan because of its broad spectrum of weed control activity and relatively low usage rates. A total of 12 SU-resistant biotypes of paddy weeds has been reported in Japan. Among them, Monochoria vaginalis is one of the most harmful paddy weeds. It is important to clarify the ecological fitness of SU-resistant biotypes of the weed, and the origin and spread of SU-resistant gene(s) for their control. The biomass and seed production of SU-resistant biotypes of M.vaginalis were compared with those of susceptible ones and clarified genetic variation of SU-resistant biotypes in Japan.To evaluate the resistance to bensulfuron-methyl, imazosulfuron and pyrazosulfuron-ethyl, elongation of new roots of nine populations under each herbicide treatment was measured. Zennoji, Kamitsuneyoshi, Maizuru, Kasai-B and Ushiku biotypes elongated new roots under the treatments, but Seika, Kameoka, Kamiseya and Kasai-A biotype … More s did not. The former five biotypes were SU-resistant and the latter four biotypes were SU-susceptible.Each seven plant of SU-susceptible and resistant biotypes was grown individually in a 1/10,000 a wagner pot. They were harvested in September, dried and weighed. Number of seeds per plant was counted. No differences were found in dry matter production and number of seeds produced per plant between SU-susceptible and resistant biotypes. Ecological fitness of SU-resistant biotypes seems not to be different from that of SU-susceptible biotypes.The genetic diversity within a population and relationship among populations were analyzed by RAPD(random amplified polymorphic DNA). There was no genetic variation among 20 individuals within each SU-resistant population of Zennoji, Kamitsuneyoshi, Maizuru, Kasai-B or Fukushima. In UPGMA tree based on simple matching coefficient, the SU-resistant populations were grouped into different clades. These results strongly suggest that SU-resistant biotypes originated independently. Less