A Dominant Gene for Thornlessness Obtained from the Chimeral Thornless Loganberry

Abstract

Abstract The thornless loganberry is a periclinal chimera in which a mutation for thornlessness apparently is confined to the outer plant layer (L1). Genetic thornless plants were obtained from this clone in Italy by selfing micropropagated plants and in New Zealand by histogenic layer manipulation. In both instances the middle plant layer (L2) apparently had been displaced by the L1 layer, so that the mutant character was transmitted by the gametes. The inheritance of thornlessness in progenies derived from this material has now been studied in Italy, New Zealand, and Scotland. In crosses, the segregation ratios did not fit closely to those expected if thornlessness were conferred by a dominant gene, largely, because thornless segregates were frequently in excess when the thornless parent was female and tended to be deficient when the latter was male. In selfings, the ratios were closer to 2:1 than to 3:1. However, the segregation of a single dominant gene for thornlessness is the most likely explanation of the results and it is proposed that the gene be designated Sfl. The homozygous dominant genotypes probably had a lower viability than the heterozygous ones.