Paraquat-Resistant Biotype of Youngia japonica (L.) DC. in Mulberry Fields in Saitama Prefecture

Abstract

1. The biotypes of Youngia japonica (L.) DC., a weed with a strong resistance to paraquat were investigated in April 1986 in mulberry fields located in Saitama Prefecture.
2. Leaf discs of such resistant plants were punched and dipped in a solution of paraquat and the degree of discoloration of the leaf in relation to the concentration of paraquat was examined. While the discs of plants tolerant to paraquat turned brown within 48 hours at a 1ppm concentration, those of the resistant plants retained their green color even at concentration of 10ppm but in some areas they displayed a brown discoloration at a paraquat concentration of 100ppm. Such a reaction was similar to that of the Erigeron philadelphicus L. and Erigeron canadensis L. plants resistant to paraquat. In addition, although the plants were resistant to diquat, the degree of resistance was lower than that to paraquat.
3. In the main sericultural zone of Saitama Prefecture, in May 1986, the distribution of Youngia japonica (L.) DC. plants resistant to paraquat was studied in mulberry fields corresponding to 235 sites in 5 areas. Although there were differences among the areas, resistant plants were recorded in 34% of the sites where they had occurred.