104
Genotype Percentage crossability with rye
kr1kr1Kr2Kr2 30–50
kr1kr1kr2kr2 >50The use of intervarietal chromosome substitution lines showed that the poor
crossability of the wheat variety Hope with rye ( S. cereale ) was determined by chro-
mosomes 5A and 5B (Riley and Chapman 1967 ). Marquis, one of the parents of the
wheat cultivar Hope, had a Kr1Kr1Kr2Kr2 genotype according to Lein ( 1943 ). The
genes Kr1 and Kr2 are located on chromosomes 5B and 5A, respectively (Riley and
Chapman 1967 ). Crossability is actively inhibited by the dominant Kr1 and Kr2
alleles of Hope and is apparently not enhanced by the recessive kr1 and kr2 alleles
of the readily crossable variety Chinese Spring (CS). The Kr1 and Kr2 alleles are
not completely dominant, but crossability is greatly reduced in heterozygotes.
Neither of the substitution lines CS/Hope 5A and CS/Hope 5B was as infertile in
crosses with rye, as the variety Hope. Consequentl y, the effects of the inhi bitors of
crossability, Kr1 and Kr2 , are either complementary or additive (Riley and Chapman
1967 ). Sasaki and Wada ( 1966 ) studied wheat-rye crossability using intervarietal
disomic substitution lines, in which pairs of chrom osomes from the poorly cross-
able cv. Cheyenne were substituted in turn into the readily crossable cv. Chinese
Spring. The substitution of chromosome 5B had a marked effect on crossability,
with an average reduction of 10.5 %. Several other chromosomes showed weaker,
variable effects, those of chromosomes 4A, 1D and 7D being the most consistent
over the 2 years and over the four lines of rye. Riley and Chapman ( 1967 ), who
were presumably unaware of study made by Sasaki and Wada, used the same
method.
The Kr1 locus was mapped using a telocentric chromosome consisting of the
long arm of chromosome 5B (Lange and Riley 1973 ). Mapping was carried out by
analyzing F 2 and testcross progenies, and it was concluded that the Kr1 locus is
located on the long arm of 5B. The location of Kr1 was co nfi rmed by Sitch et al.
( 1985 ) using the telocentric mapping technique and was found to be on the long arm
of chromosome 5B distal to the centromere with a mean recombination frequency
of 44.8 ± 3.28 %. Kr2 was shown by linkage with the major gene markers Vrn1 ,
controlling vernalization requirement, and q, controlling ear morphology to be
located on th e long arm of chromosome 5A. Kr2 is closely linked to Vrn1 , with a
mean recombination frequency of 38.1 ± 10.60 %. The similar locations of Kr1 and
Kr2 on homoeologous chromosomes suggest that these two loci are homoeoallelic.
The differences found in the recombination frequencies of the Kr1 allele on the 5B
long arm in the work of Lange and Riley ( 1973 ) and Sitch et al. ( 1985 ) could have
arisen from the use of different wheat varieties, having different 5B chromosomes
or different alleles that modifi ed crossability in the given genetic background. It
may also be that crossability was greatly infl uenced by the environment in the vari-
ous experiments.
M. Molnár-Láng