MORPHOLOGICAL AND PHYSIOLOGICAL DIFFERENCES BETWEEN THE AUXINIC HERBICIDE-SUSCEPTIBLE (S) AND HERBICIDE-RESISTANT (R) WILD MUSTARD (SINAPIS-ARVENSIS L) BIOTYPES

Physiological and morphological characteristics of an auxinic herbicide-susceptible (S) and -resistant (R) biotype of wild mustard (Sinapis arvensis L.) were examined. Plants of the R biotype were shorter, more branched, and had a smaller root system than the S biotype. Leaves of the R biotype were smaller, darker green, and had a higher chlorophyll content than those of the S biotype. The R plants, at the four-leaf stage of development, were more tolerant to cold temperature (7 degrees C) than the S biotype. The percentage of seed germination at 24, 30, and 35 degrees C was higher in the R than the S biotype. At 5 degrees C no difference in percentage of germination between the biotypes was observed, however, the R biotype seedlings were approximately two times longer than the S biotype. When compared to controls, benzyladenine and thidiazuron inhibited seedling growth of the susceptible biotype at 0.1, 1, and 10 mg/liter, whereas only concentrations of 10 mg/liter were inhibitory to the R biotype. Senescence occurred more rapidly in leaf disks of the S biotype. Furthermore, the cytokinin levels, as determined by a cucumber greening bioassay, were higher in the R than in the S biotype, suggesting that some of the differences reported may be a direct consequence of differences in hormonal equilibrium within the biotypes. (C) 1995 Academic Press, Inc.