Selection for reduced iodosulfuron sensitivity in <i>Apera spica-venti</i>

Abstract

Apera spica-venti is a genetically diverse cross-pollinated grass weed species for which increasing numbers of resistance cases towards ALS herbicides are reported in Germany. Target-site and non-target-site mechanisms are discussed to be involved. But to date, studies on resistance evolution - especially on non-target-site mechanisms involved in A. spica-venti are rare. To better understand this, a progeny population was selected from a sensitive parental population (A77) using the ALS inhibiting herbicide iodosulfuron at reduced dose rate. This progeny population was designated A77-1 and subjected to a dose-response experiment using iodosulfuron. A77-1 exhibited a decreased sensitivity to iodosulfuron compared to the parental A77 biotype (RI=2). 53% of the studied individuals of A 77-1 exhibited an ALS target-site resistance (Pro197Asn). Individuals lacking target-site resistance were identified and propagated to yield the population A 77-1-1. The coapplication of iodosulfuron and the cytochrome P450 (CYP) inhibitor malathion was able to reconstitute iodosulfuron efficacy in A 77-1-1. So, we assume that we successfully selected for target-site resistance and non-target-site resistance simultaneously. ACP-PCR was employed to identify CYPs involved in reduced sensitivity to iodosulfuron. 6 CYPs were identified.