A universal reference karyotype in rye, Secale cereale L.

Haploid, dihaploid and tetrahaploid rye plants of the variety 'Petka' have been produced to establish a homozygous genotype and karyotype. The morphology, karyotypic characteristics and the metaphase I chromosome behaviour are described demonstrating the utility of the material as a universal standard tester in rye cytogenetics. Clones of several ploidy levels are maintained by long-term in vitro sprout culture. They are available for international testing. Sexual propagation of the clones is possible using a heat treatment procedure to break the self-incompatibility of the homozygotes.