MORRISON, LAURA A.*, LISELE CREMIEUX, ROBERT S. ZEMETRA, OSCAR RIERA-LIZARAZU, AND CAROL MALLORY-SMITH. Department of Crop & Soil Science, Oregon State University, Corvallis, OR 97331-3002; Department of Plant, Soil & Entomological Sciences, University of Idaho, Moscow, ID 83844-2339. - Gene flow in the crop-weed complex of wheat (Triticum aestivum L.) and jointed goatgrass (Aegilops cylindrica Host).
Jointed goatgrass (Aegilops cylindrica Host - CD genomes), a
wild tetraploid wheat, was introduced into North America as a
contaminant of wheat seed brought from Eastern Europe in the late
1800's and early 1900's. Since its introduction, it has become a
serious crop weed in fields where hexaploid bread wheat is grown
(Triticum aestivum L. - ABD genomes). Hybridization is common
among members of the wheat complex, having played an important role in
the evolution of this allopolyploid group. Wheat and jointed goatgrass
share only the D genome. Therefore, hybrids are considered to be
sterile, a fact supported by the identification of a gametocidal
sterility system in jointed goatgrass (Endo, 1988). However, large
numbers of partially female fertile hybrids are being found in the
jointed goatgrass infested wheat fields of the Pacific Northwest.
Studies of experimental material and hybrids collected in Oregon now
suggest that neither hybridization nor seed production is a rare
event. Preliminary genetic analyses using SDS-PAGE of the high
molecular weight glutenin seed proteins, microsatellite (SSR) markers,
and genomic in-situ hybridization suggest the development of a
crop-weed complex via introgressive hybridization. To date, evaluation
of hybrid material supports the possibility of a two-way introgression
with both species capable of serving as the female parent. Wheat field
populations appear to be a diverse mix of F1 and backcross
(BC) hybrid generations. Work with experimental wheat x jointed
goatgrass BC hybrids, with either species as the recurrent male
parent, shows a rapid move to fully fertile, self-pollinating hybrids.
The wheat-jointed goatgrass weed complex offers a model system for
studying introgressive hybridization within the agricultural
ecosystem. It also offers a timely opportunity to study gene flow risk
in advance of the release of transgenic wheat.
Key words: crop-weed complex, introgression, jointed goatgrass, transgenic wheat