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I. Research Notes
Chromosome pairing in interspecific
hybrids in genus Aegilops
Patrick E. MCGUIRE
Dept. of Agronomy and Range Science University of
California, Davis, CA 95616 USA
The purpose of this report is to communicate the observed
amounts of chromosome pairing at metaphase I (MI) in hybrids
obtained from several combinations of species in the genus
Aegilops. Some of these hybrid combinations are
reported for the first time ; others have been reported
previously but usually characterized only by ranges and
modes of configurations instead of means.
Materials and Methods
Seed of the species used was obtained as indicated in
Table 1 from the collections of
the Plant Breeding Institute, Cambridge, England ; Dept. of
Plant Science, University of California, Riverside, USA ;
Agriculture Research Service, USDA, at the University of
Missouri, Columbia, USA ; and the USDA at Beltsville,
Maryland, USA.
All plants were maintained and crosses were made under
greenhouse conditions. Embryos were excised 14 days after
pollination and cultured aseptically until the two-leaf
stage on a modified (DVORAK 1981) B5 medium. Spikes of
hybrids were fixed in Carnoy's solution (6 : 3 : 1) and
anthers were squashed in acetocamine. For each hybrid,
pollen mother cells (PMCs) at MI were scored for chromosome
configurations and these scores were averaged yielding a
mean frequency per PMC for each configuration.
Genome symbols are those used by KIHARA (1982) except for U
instead of Cu as proposed by CHENNAVEERAIAH
(1960) and B instead of S as proposed by LOVE (1982). The
distinctness of the karyotype of Ae. uniaristata Vis.
from that of Ae. comosa Sibth. et Smith (M genome)
was noted by CHENNAVEERAIAH (1960) and its genome was given
the symbol L by LOVE (1982). This genome has been shown to
be involved in the tetraploid species Ae. ventricosa
Tausch by karyotype analysis (CHENNAVEERAIAH 1960), by
synthesis of an amphiploid from a hybrid between Ae.
tauschii Coss. and Ae. uniaristata which
resembled Ae. ventricosa (MATSUMOTO et al.
1957), and by chromosome pairing in a hybrid between Ae.
ventricosa and Ae. uniaristata (KIMBER et
al. 1983). Thus DL will be used here for the genomes of
Ae. ventricosa.
Results and Discussion
The use of MI chromosome pairing data from hybrids for the
purpose of genome analysis must accommodate two
considerations. One is that a certain extent of relatedness
exists between the chromosomes of any two genomes as a
result of their descent from a diploid ancestor common to
all taxa in the Triticeae. In this descent, chromosomes
become differentiated structurally and nonstructurally from
their ancestral homologues. There is evidence that
nonstructural differentiation, presumably at the nucleotide
sequence level, is the most important cause of the pairing
failure observed in hybrids within species and between
species (DVORAK & MCGUIRE 1981 ; CROSSWAY & DVORAK
1984 ; DVORAK & CHEN 1984 ; KOTA et al. 1986).
The other consideration is that most if not all polyploid
Aegilops species possess an oppositional genetic
system that regulates heterogenetic chromosome pairing to
produce diploid-like, bivalent MI pairing in those species
(MCGUIRE & DVORAK 1982).
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