In a breeding programme to combine quantitative resistance to two important potato pathogens, Phytophthora injestans causing late blight in foliage and Qlobodera pallida (the cream potato cyst-nematode), tetraploid (4 x ) offspring were obtained by crossing dihaploids, mainly as females, with tetraploids. Glasshouse and field tests in the first and second tuber-years showed that most of the offspring of highly blight-resistant dihaploids had high resistance to P. injestans. Two such dihaploids, PDH 182 and PDH 247, crossed with a tetraploid selected for high general combining ability for potato cyst-nematode (PCN) resistance, gave offspring all of which were highly blight resistant. About one third also had high PCN resistance.Detached leaflet tests were used for rapid blight resistance screening of other progenies from dihaploid x 4 x crosses in their seedling year. Differences were found in the effects of 4 x parents on the mean resistances of progenies from blight-resistant dihaploids.The results also showed differences between dihaploids in their effectiveness in transmitting blight resistance to 4 x offspring. This could be due to differences in the mode of unreduced female gamete formation, i.e. first division restitution or second division restitution (SDR). If all the unreduced gametes were produced by SDR, the differences could be due to differences in homozygosity between dihaploids with respect to blight resistance genes.The dihaploid x 4 x crosses gave few offspring per pollination. The few seedlings obtained may be offset by a higher frequency with the required characters. Since fewer seedlings would have to be grown in order to find the required combination of characters, savings could be made in planting and resistance-testing facilities over those required in conventional breeding.The tetraploid hybrids obtained can be used in a second cycle of breeding in three ways simultaneously: by crossing with other tetraploids, by crossing with dihaploids selected for complementary characters and to produce dihaploids with combined resistances.
S U M M A R YClones from the potato species Solarium phureja and 2x and 4x hybrids between S. phureja and S. tuberosum were tested for the culinary quality of their tubers following steaming, frying and baking. The quality of S. phureja tubers was high but material from the F, hybrids showed more disintegration or blackening after cooking than either parental species. Tetraploids produced by backcrossing 4x F l hybrids to S. tuberosum cultivars showed less of these defects.Fourteen 5. phureja and 2x F, hybrid clones selected for their unusual tuber skin pigmentation or shape were found to have a variety of baked flesh colours from orange-yellow to cream with red marbling. Their cooked flesh texture was generally floury and often crumbly. It is suggested that 5. phureja material could be exploited as a novel food source for specialized use in North European countries.
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