IN-VITRO AND WHOLE-PLANT MAGNITUDE AND CROSS-RESISTANCE CHARACTERIZATION OF 2 IMIDAZOLINONE-RESISTANT SUGAR-BEET (BETA-VULGARIS) SOMATIC-CELL SELECTIONS

Acetolactate synthase (ALS)-inhibiting herbicide carryover in soil can severely affect sugarbeets grown in the year(s) following application . Two newly developed imidazolinone-resistant (IMI-R) sugarbeet somati c cell selections (Sir-13 and 93R30B) were examined for magnitude of r esistance and extent of cross-resistance to other classes of ALS inhib itors and compared to a previously developed sulfonylurea-resistant (S U-R) selection, Sur. In vitro shoot culture rests indicated Sir-13 res istance was specific to imidazolinone (IMI) herbicides at approximatel y a 100-fold resistance compared to the sensitive control sugarbeet. S ur was 10,000-fold resistant to the sulfonylurea (SU) herbicide, chlor sulfuron, and 40-fold resistant to the triazolopyrimidine sulfonanilid e (TP) herbicide, flumetsulam, but not cross-resistant to the IMI herb icides. 93R30B was selected for IMI-R from a plant homozygous for the SUR allele, Sur, and displayed similar in vitro SU-R and TP-R as Sur, but also displayed a very high resistance to various IMI herbicides (4 00- to 3,600-fold). Compared to the sensitive control, Sir-13 was 300- and > 250-fold more resistant to imazethapyr and imazamox residues in soil, respectively. Response by whole plants to postemergence herbici de applications was similar to that observed in shoot cultures. Sir-13 exhibited > 100-fold resistance to imazethapyr as well as imazamox, a nd 93R30B showed > 250-fold resistance to both herbicides. 93R30B show ed great enough resistance to imazamox to merit consideration of imaza mox for use as a herbicide in these sugarbeets. Sir-13 showed a two-ro threefold higher level of resistance In the homozygous a. heterozygou s state, indicating that like most ALS-inhibitor resistance traits, it was semidominantly inherited.