CYTOGENETIC BEHAVIOUR OF ALFALFA HYBRIDS FROM TETRAPLOID BY DIPLOID CROSSES

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Abstract
Using a male-sterile tetraploid Medicago sativa plant as the female parent and 6 different diploid species as pollen parents, 5 tetraploid and 6 triploid hybrids were obtained. The tetraploid hybrids probably occurred by either non-reduction of male gametes or by digamy. Studies in F2 and back-cross populations from the tetraploid hybrids indicated that the male sterile character was controlled by a single recessive factor and that chromosome pairing was random and not restricted to chromosomes of the same parental origin. The high fertility, random chromosome pairing and tetrasomic inheritance in the tetraploid hybrids indicates that the genomes of the diploid M. sativa, M. falcata and M. hemicycla accessions are probably homologous to the genome of tetraploid M. sativa. Multivalent associations at meiosis were much higher intriploid than in tetraploid hybrids. This phenomenon is suggested to be common to many plant species and is most likely related to the presence of univalents and unsatisfied synaptic forces involved in chromosome pairing.