Location of the Benzoxazinless (bx) Locus in Maize by Monosomic and B‐A Translocational Analyses1

Abstract

The r‐X1 deficiency in maize (Zea mays L.) produces large numbers of monosomics. These monosomics are a unique and useful tool for determining the chromosome location of specific genetic loci. In this study, maize monosomics generated using the r‐X1 deficiency were used to determine the chromosome location of the benzoxazinless (bx) locus. The bx locus is deficient in the production of benzoxazin‐3‐one glucosides, which have been positively correlated with resistance to first‐brood European corn borers, corn leaf aphids, and resistance to northern corn leaf blight. F1 progeny of R/r‐X1; Bx/Bx females crossed by r/r; bx/bx males were screened for monosomic plants expressing the bx phenotype. Karyotypic analysis indicated the monosomic chromosome in such plants was chromosome 4; thus, the bx locus is on chromosome 4. B‐A translocations were then used to confirm the above observation and to determine that the bx locus is in the short arm of chromosome 4. Conventional linkage analysis placed the locus as probably being near Rp4.