MISDIVISION OF AN AGROPYRON CHROMOSOME

Abstract

Agrotricum lines, in which an Agropyron chromosome with genes for stem- and leaf-rust resistance replaced wheat chromosome 6D, have been used in breeding programs at the University of Nebraska-Lincoln. The 42-chromosome Agrotricum lines were developed by an initial cross between common wheat (Triticum aestivum) and Agropyron elongatum (2n = 70), followed by backcrosses to various wheat cultivars. These lines were crossed as male parents with Chinese Spring monosomic 6D as female, to obtain plants monosomic for the Agropyron chromosome (20″ + 1′Ag). Microsporocytes in these monosomic alien substitution plants were examined at the first and second divisions of meiosis. The Agropyron chromosome is a small, nearly isobrachial chromosome. It misdivided in 40.1% of the cells at the first division (AI-TI). Meiotic configurations of the misdividing chromosome indicated that the centromere of the Agropyron chromosome is divisible into four functional units (telocentrics) at the first division. Only 11.6% of the cells with lagging chromosomes showed misdivision at the second division (AII-TII) of meiosis. The expected frequency of micronuclei from AII-TII data was compared with that observed at the quartet stage. It was concluded that 24% of the lagging whole or telocentric chromosomes were included in the second division nuclei, indicating that some of the telocentrics may be transmitted. The relatively high rate of misdivision of the Agropyron chromosome considerably increases the chances of recovering telo- and isosomic lines for each arm. Rust tests of these lines will provide evidence for the locations of genes for stem- and leaf-rust resistance on specific arms of this chromosome.