writes
goatgrass (Aegilops cylindrica)
http://www.agf.gov.bc.ca/cropprot/weedguid/joingoat.htm

Is a pretty picture of goatgrass.


http://www.intl-pag.org/pag/10/abstracts/PAGX_W243.html
NATURAL GENE INTROGRESSION BETWEEN PLANT SPECIES

========================

The ability to transfer genes between related plant species has been a
great benefit in the improvement of cultivars for disease resistance,
insect resistance, and/or end-use quality. This has been especially true
in allopolyploid species where there are multiple species that can act
as donors. The ability of these species to intercross and produce
hybrids has become a concern with the advent of herbicide resistant
cultivars. The potential for the development of herbicide resistant
weeds due to gene flow from a cultivated species has raised questions
concerning the release of cultivars with traits that could improve the
competitiveness of weedy species. In canola (Brassica napus), gene
transfer between canola and field mustard (B. rapa) has been
demonstrated in the field. When grown in close proximity, over 4.5% of
field mustard seed screened expressed a transgene from the adjacent
canola through canola x field mustard crossing. Reproductive fitness of
initial hybrids was poor, but fitness increased dramatically after
backcrossing. In wheat (Triticum aestivum), hybridization of wheat and
jointed goatgrass (Aegilops cylindrica) has been observed for years. It
has recently been demonstrated that backcrossing can occur in the field
and that only two backcrosses to jointed goatgrass are necessary to
restore partial self-fertility. This indicates that gene introgression
could occur between these species. Work is currently underway to
determine if genome location of the resistance gene in allopolyploids
can be used to minimize the potential for gene movement. Ultimately it
may require both gene placement and proper crop management to reduce the
potential of gene flow from cultivated species to weedy species,
maximizing the benefits of gene introgression while minimizing the
detrimental effects of natural gene flow.

===============

I gave you an example of a noxious weed and a common crop but
intercrossing between monocot species is not rare at all.

The canola one is well known and is why I am against insecticide gene
transfer in european rape.

The goatgrass cross is infertile. It took literally 20 years of complex
interbreeding and selection to move a single goatgrass gene into wheat.
It's not common and last I heard natural goatgrass had no wheat genes in
it, which is unlike the case for brassica adjacent to rape.

It provided, IIRC, some eyespot resistance for a decade or so.

--
Oz
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