Evolved resistance to acetolactate synthase–inhibiting herbicides in common sunflower (Helianthus annuus), giant ragweed (Ambrosia trifida), and shattercane (Sorghum bicolor) in Iowa

• Published in: Weed science 2004-08, Vol.52 (4), p.538-548
• Main Authors: Zelaya, Ian A., Owen, Micheal D. K.
• Format: Article
• Language: English
• Subjects: 2-Acetolactate accumulation; acetohydroxyacid synthase; acetolactate synthase; acetolactate synthase inhibiting herbicides; AHAS; Ambrosia trifida; asexual reproduction; biotypes; broadleaf weeds; cross resistance; diacetyl chromophore; grass weeds; Helianthus annuus; herbicide-resistant weeds; herbicides; imidazolinone herbicides; in vivo assay; natural selection; plant growth; selection pressure; Sorghum bicolor; sulfonylurea herbicides; triazolopyrimidine sulfoanilide herbicides; WEED BIOLOGY AND ECOLOGY; Westerfeld's test
• ISSN: 0043-1745; 1550-2759
• DOI: 10.1614/WS-03-113R1

Weed biotypes putatively resistant to acetolactate synthase (ALS)–inhibiting herbicides were reported by Iowa farmers from 1997 to 2001. Greenhouse studies confirmed cross-resistance to triazolopyrimidine sulfonanilide and sulfonylurea (SU) herbicides in giant ragweed from Scott County, IA (Werner Farm), which corresponded to resistance to susceptibility (R:S) GR50 (50% growth reduction) ratios of 21 and 28 to cloransulam and primisulfuron + prosulfuron, respectively. At the enzyme level, this represented a 49- and 20-fold I50 (50% enzyme inhibition) increase. Cross-resistance to imidazolinone (IMI) and SU herbicides was also observed in common sunflower from Cherokee, IA. Compared with a susceptible biotype, the resistant common sunflower biotype demonstrated GR50 R:S ratios of 36 and 43 to imazethapyr and chlorimuron, respectively. Shattercane from Malvern, IA, was susceptible to nicosulfuron but was resistant to imazethapyr (GR50 R:S ratio = 29). The woolly cupgrass biotypes from Union County, IA (Pettit Farm and Travis Farm), were reportedly resistant but were identified susceptible to both IMI and SU herbicides. Using an in vivo ALS assay, extractable endogenous 2,3-diketone concentrations ranged from 25 to 71 nmol g−1 fresh weight for all species. Compared with susceptible biotypes, 2,3-diketone levels accumulated to at least twofold higher levels in treated resistant plants 120 h after herbicide application. Field history data suggested that resistance evolved independently in three environments where ALS-inhibiting herbicides represented an important component of the selection pressure. Nomenclature: Chlorimuron; cloransulam; imazapyr; imazethapyr; nicosulfuron; primisulfuron; prosulfuron; common sunflower, Helianthus annuus L. HELAN; giant ragweed, Ambrosia trifida L. AMBTR; shattercane, Sorghum bicolor (L.) Moench SORVU; woolly cupgrass, Eriochloa villosa (Thunb.) Kunth ERBVI.