Abstract
Investigation of segregation in respect to seed-coat color in F2 of 22 different hybrids was made, which were originated from crosses among 20 varieties of Japanese and foreign origin, including 3 red-grained, 1 brown-grained and 16 white-grained ones.
In the crosses red-grained (Rc Rd)× white-grained (rc rd) F2 segregation took place normally, i.e. red:brown:white=9:3:4. Other crosses between red (Rc Rd) and white (rc Rd) gave the ratio approximately red:white=3:1, but there were always found a small number of unexpected brown segregants, showing the possibility of occurrence of plants lacking Rd-locus. In the crosses red (Rc Rd)×red (Rc Rd) also a few number of unexpected brown segregants were noticed.
Discussion was made as to the mechanism which resulted in the appearance of segregants lacking Rd-locus. It has been suggested that the cause might be due to occurrence of auto-and allosyndesis, involving the chromosome which bears Rd-locus. The partner of the Rd-bearing chromosome in autosyndesis can, however, not be identified.
The genotype of brown-grained variety, Surjamkhi, was determined as RcdRd, Rcd being a new allele at Rc-locus. The multiple allelic series here proposed is as follows; Rc>Rcd>rc.
