SEMIDOMINANT NATURE OF MONOGENIC SULFONYLUREA HERBICIDE RESISTANCE INSUGAR-BEET (BETA-VULGARIS)

Greenhouse and laboratory studies were conducted to determine the degr ee of dominance of the monogenic sulfonylurea herbicide resistance tra it in diploid sugarbeet by comparing the response of homozygous and he terozygous resistant sugarbeet to primisulfuron, thifensulfuron, and c hlorimuron on the whole plant and acetolactate synthase (ALS) enzyme l evel. Progeny tests suggested that the monogenic sulfonylurea herbicid e resistance was semidominant. Subsequently, heterozygous resistant (R -1) and homozygous resistant (R-2) sugarbeet lines were sprayed with i ncreasing rates of primisulfuron, thifensulfuron, and chlorimuron, and herbicide rates required for 50% growth reduction (GR50) were determi ned. GR50 values were also determined for homozygous susceptible sugar beet lines (S-1 and S-2). The GR50 values indicated that the R-2 sugar beet was 377, 269, and 144 times more resistant to primisulfuron, thif ensulfuron, and chlorimuron, respectively, than susceptible S-2 sugarb eet. In contrast, R-1 sugarbeet was only 107, 76, and 57 times more re sistant to primisulfuron, thifensulfuron, and chlorimuron, respectivel y, than S-1 sugarbeet, indicating at least a twofold difference in the magnitude of resistance between homozygous resistant and heterozygous resistant sugarbeet lines. ALS enzyme activity analysis were consiste nt with whole plant results. Thus, based on these two, maximum crop re sistance can be obtained by developing homozygous resistant cultivars.