106
parents. Leighty and Sando ( 1928 ), Lein ( 1943 ), Marais and Pienaar ( 1977 ) and
Tanner and Falk ( 1981 ) also reported earlier that hybrids between Chinese Spring
and wheats with low rye crossability exhibited intermediate levels of crossability
with rye. It was confi rmed that plants with the heterozygous K1kr1 Kr2kr2 allele
combination had better seed set with rye than homozygous Kr1Kr1 Kr2Kr2 geno-
types, suggesting that the dominance of the Kr alleles is not complete.
The wheat cultivars Chin ese Spring and Hope were crossed with the barley
( Hordeum vulgare L.) cultivar Betzes by Fedak and Jui ( 1982 ) to establish the level
of crossability. The complete set of Chinese Spring/Hope chromosome substitution
lines was used to identify chromosomes carrying genes responsible for the cross-
ability of Chinese Spring with Betzes. No progeny were obtained from the
Hope × Betzes cross indicating that this combination was incompatible. Hybrids
were obtained from the Betzes × Chinese Spring combination at rates of 48.9 % and
0.78 % of pollinated fl orets for seeds and seedlings, respectively. No progeny were
obtained from substitution lines 5A, 5B, and 5D, even though large numbers of
fl orets were pollin ated, indicating that the chromosomes of Chinese Spring
homoeologous group 5 are the major chromosomes responsible for permitting
crossability with Betzes barley. Other chromosomes of Hope had minor effects on
crossability with barley. A number of wheats varying in wheat- rye crossability were
selected as female parents for interspecifi c and intergeneric crossess by Thomas
et al. ( 1980 ). A number of species more or less closely related to common wheat
were selected as male parents ( Secale cereale , S. montanum , Aegilops ovata , Ae.
variabilis , Triticum timopheevii , T. turgidum , T. monococcum , Agropyron junceum ,
A. elongatum , Elymus giganteus , E. arenarius ). The wheat genes best known for
reducing seed set in crosses with cultivated rye also prevent the pollen of other
related species from setting seed on common wheat. This correlation between inter-
specifi c crossabilities is general in common wheat and is not restricted to Chinese
Spring, Hope and their joint derivatives. Average seed set was lower when more
distantly related taxa were used as pollen parents. Thus, low wheat-rye crossability
in common wheat was not a serious barrier to hybridization with emmer ( T. turgi-
dum var. dicoccum ), but even high wheat-rye crossability did not guarantee high
rates of seed set in crosses with Elymus species (Thomas et al. 1980 ). Genes for low
interspecifi c crossability in wheat act against a wide spectrum of potential pollina-
tors. The use of common wheats with high wheat-rye crossability in interspecifi c
hybridization will increase the recovery of hybrids in many wide crosses.
When diploid, tetraploid and hexaploid Triticum species were pollinated with rye
by Kiss and Rajháthy ( 1956 ), the highest seed set was achieved for the hexaploid
species ( Triticum aestivum , T. spelta ), and the lowest seed set for di plo id species
( T. monococcum , T. boeticum ). T. durum and T. carthlicum gave higher seed set with
rye than T. timopheevii , T. turgidum , or T. dicoccum (Kiss 1966 ). A wheat line with
high crossability with rye, selected from the Hungarian wheat cultivar Bánkúti
1201, gave more than 40 % crossability with rye in the fi eld over several years (Kiss
and Rédei 1952 ; Kiss 1953 ; Kiss and Rajháthy 1956 ). In a study on how genetic
variation in tetraploid wheat and rye infl uenced crossability, Halloran ( 1981 ) found
that the crossability of the tetraploid wheat T. turgidum (L.) Thell. ssp. turgidum
M. Molnár-Láng