SELECTION OF DIPLOID TUBEROUS SOLANUM HYBRIDS FOR 2N-EGG FORMATION USING 2X-CENTER-DOT-4X-CROSSES

Diploid families of Tuberosum hybrids as well as Tuberosum-wild specie s Fl hybrids were generated to select 2n-egg producing genotypes of di fferent genetic backgrounds. Plants were selected if they produced mor e than four seeds per berry after pollination with tetraploid males (2 x.4x-crosses). From the nine families of Tuberosum hybrids that were d erived from one or two 2n-egg producing parents, 12 out of 82 (15%) 2n -egg producing plants were selected. From the 32 families of Tuberosum -wild species F-1 hybrids, 21 of 274 (8%) 2n-egg producing plants were selected. The level of 2n-egg formation was estimated in 25 selected diploid hybrids and five control clones (three high, one moderate and one low 2n-egg producers) on the basis of seed set following 2x.4x-cro sses using 13 tetraploid males in four crossing years. Besides the eff ect of the diploid 2n-egg producing female on the seed set following 2 x.4x-crosses (P = 0.0001), there was a significant effect of the tetra ploid male (P = 0.0001), whereas the effect of the crossing year (P = 0.0688) was less significant. On the basis of differences in the seed set following 2x.4x-crosses as compared to the control clones for low, moderate and high level of 2n-egg formation, the level of 2n-egg form ation in two of the newly selected hybrids was classified as very high , four were high, sixteen were moderate and three were low. The signif icance of the selected hybrids for the genetic analysis of various res titution mechanisms of 2n-egg formation is discussed.