2 DISTINCT ALLELES ENCODE FOR ACETYL-COA CARBOXYLASE INHIBITOR RESISTANCE IN WILD OAT (AVENA-FATUA)

The objectives of this study were to determine the inheritance of aryl oxyphenoxypropionate (APP) resistance in the wild oat population UM33 and to determine the genetic relationship between resistance in UM33 a nd another population, UM1, which has a different cross-resistance pat tern. Reciprocal crosses were made between UM33 and a susceptible popu lation UM5, and between UM33 and UM1. Initial screenings of F-1 and F- 2 populations derived from crosses between UM33 and UM5 were conducted over a range of fenoxaprop-P rates to determine a discriminatory dosa ge. F-2 populations and F-2-derived F-3 families were then screened at this dosage (1200 g ai ha(-1)) to determine segregation patterns. Res ults from reciprocal UM33 x UM5 F-1 dose-response experiments, and F-2 and F-2-derived F-3 segregation experiments indicated that UM33 resis tance to fenoxaprop-P was governed by a single, partially dominant nuc lear gene system. To determine if resistance in UM1 and UM33 results f rom alterations at the same gene locus, 584 F-2 plants derived from re ciprocal UM33 x UM1 crosses were screened with 150 g ha(-1) fenoxaprop -P. This dosage was sufficient to kill susceptible plants (UM5), but w as not sufficient to kill plants with a resistance allele from either parent. None of the treated F-2 plants exhibited injury or death, indi cating that UM1 and UM33 resistance genes did not segregate independen tly. From this it was concluded that resistance in both populations is encoded at the same gene locus.