Numerically unreduced (2n) gametes from first division restitution (FDR) are considered to be superior to 2n-gametes from second division restitution (SDR) because they transfer a larger proportion of the total parental heterozygosity and epistasis intact to the tetraploid progeny. This supposed superiority was investigated by comparing 12 sets of reciprocal 4x-2x crosses. Each diploid parent used in a reciprocal set produced 2n-pollen by FDR and 2n-eggs by SDR. Six agronomic characters were investigated. FDR progenies (from 4x.2x) were found to have higher mean yields due to more and bigger tubers. With respect to underwater weight, the overall progeny mean of FDR progenies was significantly higher than that of SDR progenies (from 2x.4x). However, the absolute difference found between both overall progeny means was too small to be of practical significance. No differences between FDR and SDR progeny means were found for vine maturity and chip colour. In addition to the progeny mean, within-progeny variation is important in potato breeding. For vine maturity a higher within-progeny variation was detected in SDR progenies, whereas within-progeny variations for yield, underwater weight and chip colour were not different in FDR and SDR progenies. With regard to vine maturity, we conclude that SDR 2n-gametes are superior to FDR 2n-gametes because, with the same progeny means of FDR and SDR progenies, the within-progeny variation was higher in SDR progenies. Therefore the assumed superiority of FDR 2n-gametes was confirmed for yield but was not observed for vine maturity, underwater weight and chip colour.

Selection criteria for agronomic characters in a potato breeding program at the diploid (2x) level may differ from selection criteria used when selecting breeding lines at the tetraploid (4x) level . Differences between selection criteria are expected, (1) when expression of the characters is different at both ploidy levels and/or (2) when the effect of diploid breeding lines on agronomic characters of tetraploid progenies is different from the effect of tetraploid breeding lines . In this investigation sets of diploid and tetraploid progenies, each set derived from the same 2x .2x cross, were compared as to the expression of six agronomic characters . Diploid progenies had significantly lower yields (due to smaller tubers) and significantly higher under water weights than tetraploid progenies . Vine maturity and chip colour were similarly expressed at both ploidy levels . Correlations between yield and yield components, and between under. water weight and chip colour were similar at both ploidy levels . The lower yields and higher under water weights found in diploids point to the need of different selection criteria for selecting diploid and tetraploid breeding lines .

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The parental effects on progenies from potato 4x .2x(FDR) crosses were analyzed to determine whether and to what extent selection criteria used for selecting tetraploid breeding lines have to be adjusted when selecting diploid breeding lines. For vine maturity and chip colour multiple regression analysis of progeny means on means of diploid and tetraploid parents revealed high coefficients of determination (R2 ) for both characters, indicating good predicting power of the performance of both diploid and tetraploid parents on the performance of their 4x .2x progenies . For vine maturity the multiple regression slope for the tetraploid parents was significantly larger than for the diploid parents, and progeny means were towards the tetraploid parents . This indicates that selection criteria for vine maturity may be less stringent at the diploid level . However, diploids may be earlier maturing than tetraploids and therefore selection criteria can better be similar at both ploidy levels . For chip colour, multiple regression slopes for diploid and tetraploid parents were similar and progeny means were towards the darkest coloured parent irrespective of its ploidy level . This indicates that selection of breeding lines for chip colour can be conducted similarly at both ploidy levels . 175