Breeding systems in Stylosanthes. I. Observations of outcrossing in S. scabra at an alcohol dehydrogenase locus

Abstract

A polymorphism for seed alcohol dehydrogenase (ADH) occurs in Stylosanthes scabra CPI 40205, a species currently being evaluated for cattle grazing in North Queensland. S. scabra (2n = 40) is normally a true breeding fixed heterozygote at the Adh locus, consistent with it being a partial or complete allotetraploid. The polymorphic population contains fixed heterozygotes (typical for the species), simplex heterozygotes and slow homozygotes. An estimate (¦ s.e.) of outbreeding amongst the progeny of homozygotes is t = 1.8 ¦ 0.45 %. The origin of the polymorphism is unclear, but it is suggested that an event (possibly some form of hybridization) during the seed multiplication phase broke down the preferential pairing which is presumed to be the basis of the stabilized heterozygosity of the allotetraploid.