CELL SELECTION AND INHERITANCE OF IMIDAZOLINONE RESISTANCE IN SUGAR-BEET (BETA-VULGARIS)

Sugarbeets are sensitive to imidazolinone herbicide residues applied t o rotational crops. Two imidazolinone-resistance (IMI-R) sugarbeet tra its were developed by somatic cell selection to overcome rotation rest rictions for sugarbeets where imidazolinones have been applied. Sir-13 is an IMI-R/SU-S (sulfonylurea-sensitive) variant selected from an im idazolinone-sensitive (IMI-S) sugarbeet clone, REL-1. A second variant , 93R30B, resistant to imidazolinone as well as to sulfonylurea herbic ides (IMI-R/SU-R), was selected from a plant homozygous for a previous ly described sulfonylurea-specific resistance trait, Sur (IMI-S/SU-R). The IMI-R alleles (Sir-13 and 93R30B) were found to be corresponding allelic variants at the same ALS locus and both were tightly associate d with the Sur allele. Each resistant allele is dominant to the sensit ive wild-type allele; however, incomplete dominance is shown among res istance alleles. Diploid sugarbeet contains a single ALS gene copy, li miting the ability to stack these resistance traits in the same plant by traditional breeding.