Discovery of a primisulfuron-resistant shattercane (Sorghum bicolor) biotype

Shattercane seeds were collected in 1992 from 16 fields in southeastern and south-central Nebraska that had been treated for 3 consecutive yr with primisulfuron or nicosulfuron. Approximately 11,200 planes, from a total of 16,000 seeds (1,000 per field) planted, were evaluated for primisulfuron resistance in greenhouse screening. A single resistant plant was found. No other primisulfuron resistance was found in evaluating an additional 1,718 plants from the remaining seeds collected in 1992 from the field where the original resistant plant was found. Shattercane seeds were collected in 1993 and 1994 from that field. All 17,038 plants from these collections were killed by primisulfuron. A field assessment of 118 descendents of the original resistant plant (S(1) progeny) produced three responses to primisulfuron at an approximate 1:2:1 ratio: (1) death; (2) some inter-veinal chlorosis; or (3) no visible injury or symptoms. Discovery of this resistant shattercane biotype indicates the potential for selection of primisulfuron-resistant shattercane populations under field conditions.