RESPONSE OF MAIZE (ZEA-MAYS) INBREDS AND HYBRIDS TO RIMSULFURON

Extensive glasshouse studies characterized the varietal response to rimsulfuron of 37 inbreds of maize (Zea mays L.), representing the major inbred families used in hybrid seed production, and 20 defined hybrids from these inbreds. Tolerant hybrids were produced when one or both of its parents were tolerant. Sensitive hybrids occurred only when both parents were sensitive. Genetic analysis indicated that sensitivity is controlled by a single recessive gene. Dose-response analysis showed varieties could vary more than 40 000-fold in sensitivity. Only the AHAS-modified variety with the XA-17 gene had changed enzymes sensitivity. This gene provided crop tolerance to very high rates of rimsulfuron and its interaction with an organophosphate insecticide. Breeders can eliminate varietal sensitivity in three ways: always use at least one tolerant hybrid parent, backcross sensitive inbreds with tolerant, or use an AHAS-modified gene.