Selection from Solanum tuberosum group phureja of genotypes combining high-frequency haploid induction with homozygosity for embryo-spot

Abstract

In this article the term ‘pollinators’ refers to diploid genotypes of Solanum tuberosum Group Phureja which are used to pollinate autotetraploid potatoes for the induction of autonomous growth of unfertilized egg cells. Plants obtained from such egg cells contain chromosomes of the female only and are called dihaploids. The successful selection of ideal pollinators from Group Phureja is described. A pollinator is considered to be ideal, if it has good male fertility, homozygosity for the dominant seed marker embryo-spot and the ability to induce in autotetraploid cultivars a high number of dihaploids both per berry and per 100 seeds. Embryo-spot is a deep purple or reddish coloration at the base of the cotyledons of the embryo, visible on both sides of the flat seeds. It is one manifestation of a set of complementary genes with pleiotropic action, causing a concentration of anthocyanins at the base of all plant organs that are homologous to leaves. The complementary genes are: a basic gene P for anthocyanin production (this is the seedling marker ‘coloured hypocotyl’) and allele B d of locus B. Thirty-three homozygous B d B d PP plants and 41 B d bPP plants were identified and a number from both classes tested as pollinator onto varieties. Among the homozygous group a number of ‘ideal pollinators’ could be detected. Unexpectedly a few polyploids grew from spotless seeds when using homozygous pollinators on varieties; 1.4% showed purple hypocotyl and 2.6% were matroclinous. The latter group of polyploids probably may have arisen from ‘unreduced’ egg cells of the cultivars used. In the progenies from crosses between recessive cultivars (bbbbpppp) and heterozygous pollinators (B d bPP) the ratio of spotted: spotless hybrid seeds appeared to deviate greatly from 1:1. This is ascribed to ‘unreduced’ gametes, which originate during meiosis, presumably through lack of formation of the ‘reductional’ (= first division) cell wall. On this assumption a map distance of 30 and 24 cross-over units is estimated for locus B on the basis of the proportion of nulliplex tetraploid hybrids in two different crosses. High- and low-seed-set pollinators were found at a ratio of 8:21 suggesting monogenic dominance of low seed-set. Seeds per berry and haploids per berry are significantly correlated using low-seed-set pollinators on cultivars, but they are not when pollinators are used that produce high numbers of seeds per berry. A hypothesis is put forward to explain this phenomenon.