Cytogenetic Characterization of Perennial Wheat Breeding Lines.

Perennial wheat has been proposed to alleviate long standing issues with soil erosion in dryland cropping systems while supporting rural communities and providing grain farmers with a marketable crop.  Current efforts to develop perennial wheat at Washington State University have focused on interspecific crosses between winter wheat (Triticum aestivum L.) and wild perennial grasses such as Thinopyrum elongatum and Th. ponticum. Between 1995 and 2003, several hundred interspecific progeny were created by crossing several different cultivars of winter wheat with Th. ponticum. The cytogenetics of these aneuploid lines were not previously characterized limiting their utility as parents and stable breeding lines. Using cytogentic techniques, the mitotic chromosome number and species origin of chromosomes was determined for 12 breeding lines, and the amount of sequence variation of these breeding lines was estimated using AFLPs. Those lines were intercrossed with each other to produce 20 families and the level of chromosome pairing during meiosis I was measured in the F1 progeny. Additionally, the self-pollination and outcrossing rates were estimated for those breeding lines.  The lines contained between 44 and 64 chromosomes, of which 8 to 16 are from Th. ponticum. An analysis of molecular diversity using the AFLP data indicated a high level of genetic diversity both within and across breeding lines (88% and 12%, respectively) and two distinct populations separated by a generation of self-fertilization. The outcrossing rate was estimated at 16%. Understanding the chromosome number and origin is necessary for developing a population of breeding lines that can be used as parents.  Despite the variable number of chromosomes across lines and the formation of multivalents and single chromosomes during meiosis, these lines undergo stable reproduction marked by the formation of viable seeds and development of fertile progeny. We hypothesize that the input of genetic material from outcrossing helps reduce infertility and low seed set in these aneuploid breeding lines.