Jointed goatgrass is a major weed in the wheat-producing areas of the western U.S. It shares the D genome with wheat, and interspecific hybrids between the two species occur in the field. The objective of this research was to determine if wheat X jointed goatgrass hybrids could serve to transfer genes from wheat to jointed goatgrass. A backcrossing program was initiated in the greenhouse between wheat X jointed goatgrass hybrids and either jointed goatgrass or wheat to determine the potential for seed set and the restoration of self-fertility. Seed was set by backcrossing with either species as the recurrent parent. Female fertility increased from 2% in the hybrid to 37% in the BC2 plants with jointed goatgrass as the recurrent parent. Partial self-fertility was restored in the second backcross (BC2) generation using jointed goatgrass as the recurrent parent. This indicates that genes could be transferred between wheat and jointed goatgrass after only two backcrosses. The number of bivalents observed in the plants during meiosis appeared to be key to increasing female fertility and self-fertility. Based on the results of this study, it is possible for genes to move from wheat to jointed goatgrass. Any release of a herbicide-resistant wheat should be accompanied by a management plan that would minimize the potential for gene movement between these species.

The spontaneous flow of genes from wheat to jointed goatgrass is of great concern to breeders intending to release herbicide-resistant wheat. The objectives of this research were to study how genes could flow from wheat to jointed goatgrass through crossing and backcrossing between these two species and, based on this knowledge, to propose possible ways to minimize the chance of gene flow between them. Results showed that the wheat × jointed goatgrass hybrid can only serve as a female parent to produce the BC1 generation. The BC1 generation was found to have 1.8% male fertility and 4.4% female fertility, indicating that it could serve as either the male or female parent to produce a BC2 generation. The fertility of the resultant BC2 generation further increased. The average male, female, and self-fertility was 8.9, 18.0, and 6.9%, respectively. After the BC2 generation, the backcross progeny has three possible ways to reproduce: to pollinate jointed goatgrass, to be pollinated by jointed goatgrass, or to pollinate itself. Restoration of the chromosome number of jointed goatgrass continues as the BC2 generation is selfed, but some plants can contain an alien chromosome over generations. The possible ways to reduce the chance of gene flow between these two species are (1) prevent the production of hybrids, (2) prevent the production of the BC1 generation, and (3) put a herbicide-resistant gene on the A- or B-genome of wheat.

Hansen, Jennifer L.; Zemetra, Robert S.; Santra, Dipak K.; Campbell, Kimberly G.; and Riera-Lizarazu, Oscar, "Identification of a candidate gene for the wheat endopeptidase Ep-D1 locus and two other STS markers linked to the eyespot resistance gene Pch1" (2008 Abstract Wheat is prone to strawbreaker foot rot (eyespot), a fungal disease caused by Oculimacula yallundae and O. acuformis. The most eVective source of genetic resistance is Pch1, a gene derived from Aegilops ventricosa. The endopeptidase isozyme marker allele Ep-D1b, linked to Pch1, has been shown to be more eVective for tracking resistance than DNA-based markers developed to date. Therefore, we sought to identify a candidate gene for Ep-D1 as a basis for a DNA-based marker. Comparative mapping suggested that the endopeptidase loci Ep-D1 (wheat), enp1 (maize), and Enp (rice) were orthologous. Since the product of the maize endopeptidase locus enp1 has been shown to exhibit biochemical properties similar to oligopeptidase B puriWed from E. coli, we reasoned that Ep-D1 may also encode an oligopeptidase B. Consistent with this hypothesis, a sequence-tagged-site (STS) marker, Xorw1, derived from an oligopeptidase B-encoding wheat expressed-sequence-tag (EST) showed complete linkage with Ep-D1 and Pch1 in a population of 254 recombinant inbred lines (RILs) derived from a cross between wheat cultivars Coda and Brundage. Two other STS markers, Xorw5 and Xorw6, and three microsatellite markers (Xwmc14, Xbarc97, and Xcfd175) were also completely linked to Pch1. On the other hand, Xwmc14, Xbarc97, and Xcfd175 showed recombination in the W7984 £ Opata85 RIL population suggesting that recombination near Pch1 is reduced in the Coda/Brundage population. In a panel of 44 wheat varieties with known eyespot reactions, Xorw1, Xorw5, and Xorw6 were 100% accurate in predicting the presence or absence of Pch1 whereas Xwmc14, Xbarc97, and Xcfd175 were less eVective. Thus, linkage mapping and a germplasm survey suggest that the STS markers identiWed here should be useful for indirect selection of Pch1.

No abstract

Field experiments were conducted to determine if seeds would be produced on Triticum aestivum by Aegilops cylindrica hybrids in the field and, if it were, to determine the viability of the seeds produced. One, five, or 10 hybrids were planted into varying proportions of A. cylindrica and T. aestivum in a replacement series design. Percent seed set ranged from 0 to 5.5% in 1996 and from 0 to 9.2% in 1997. Seeds were set in all treatments. The average seed set was 2.3% in 1996 and 3.8% in 1997. No differences in seed set were found among treatments. The seeds produced were separated according to seed condition, either full or shriveled, and tested for germination. The germination of the seeds produced on the hybrids was not significantly different between years. The average germination for full seeds was 94% in both years and 79 and 84% for shriveled seeds in 1995 and 1996, respectively. Greenhouse studies were conducted to evaluate the rate of self-fertility of the BC1 generation and to identify morphological characteristics that could be used to identify the probable pollen donor parent and to predict the occurrence of seed set. In 1997 4.1% and in 1998 2.1% of BC1 plants set seeds. The average seed set was 0.3% in 1997 and 0.06% in 1998. It was not possible, using any morphological characteristic measured, to determine the identity of the parent serving as the pollen donor in the previous generation or to predict the occurrence of seed set in the BC1 generation. This is the first reported study to show that hybrids between T. aestivum and A. cylindrica have the ability, although limited, to backcross under field conditions and set seeds. Furthermore, the seeds produced are viable and will germinate and produce plants. With the millions of hectares of T. aestivum infested with A. cylindrica, even the limited ability to backcross is of concern for the movement of a herbicide-resistance gene.