A Physically Anchored Genetic Map and Linkage to Avirulence Reveals Recombination Suppression Over the Proximal Region of Hessian Fly Chromosome A2

Abstract

Resistance in wheat (Triticum aestivum) to the Hessian fly (Mayetiola destructor), a major insect pest of wheat, is based on a gene-for-gene interaction. Close linkage (3 Ϯ 2 cM) was discovered between Hessian fly avirulence genes vH3 and vH5. Bulked segregant analysis revealed two DNA markers (28-178 and 23-201) within 10 cM of these loci and only 3 Ϯ 2 cM apart. However, 28-178 was located in the middle of the short arm of Hessian fly chromosome A2 whereas 23-201 was located in the middle of the long arm of chromosome A2, suggesting the presence of severe recombination suppression over its proximal region. To further test that possibility, an AFLP-based genetic map of the Hessian fly genome was constructed. Fluorescence in situ hybridization of 20 markers on the genetic map to the polytene chromosomes of the Hessian fly indicated good correspondence between the linkage groups and the four Hessian fly chromosomes. The physically anchored genetic map is the first of any gall midge species. The proximal region of mitotic chromosome A2 makes up 30% of its length but corresponded to Ͻ3% of the chromosome A2 genetic map.

A Neo-Sex Chromosome That Drives Postzygotic Sex Determination in the Hessian Fly (Mayetiola destructor)

“…Upon determining the sequence of this band, we recognized that it was identical to marker 2709 (GenBank accession no. BV079629), an AFLP that had been mapped previously within a cluster of 12 AFLPs near the telomere of the long arm of Hessian fly polytene chromosome A1 (Behura et al 2004). In that study, we noted the long arm of A1 (A1q) appeared to have a relatively low rate of genetic recombination.…”

“…Hessian fly populations: Hessian fly strains were maintained and experimental matings were performed as previously described (Behura et al 2004). Because Cm's effect is maternal, the Cm genotype of each female is manifested as the phenotype (sex) of her offspring.…”

“…AFLP-polymerase chain reaction (PCR) fingerprinting of individual Hessian flies was performed as previously described (Behura et al 2004), using the AFLP-based Genome Typing Kit for small plant genomes (Invitrogen, Carlsbad, CA). The AFLP band that cosegregated with the thelygenic Hessian fly genotype was amplified using the selective primers EcoRI-AC and MseI-CTG.…”

“…Molecular cytogenetics: BAC library screening and polytene chromosome preparations were performed as previously described (Behura et al 2004). BAC clones were derived from three BAC libraries, the Hf library (X. M. ), the Mde library (Behura et al 2004), and the CL library ).…”

“…BAC clones were derived from three BAC libraries, the Hf library (X. M. ), the Mde library (Behura et al 2004), and the CL library ). Fluorescence in situ hybridization (FISH) to Hessian fly polytene chromosomes was performed using BAC DNA probes.…”