The third most important food crop worldwide, potato (Solanum tuberosum L.) is a tetraploid outcrossing species propagated from tubers. Breeders have long been challenged by polyploidy, heterozygosity, and asexual reproduction. It has been assumed that tetraploidy is essential for high yield, that the creation of inbred potato is not feasible, and that propagation by seed tubers is ideal. In this paper, we question those assumptions and propose to convert potato into a diploid inbred line-based crop propagated by true seed. Although a conversion of this magnitude is unprecedented, the possible genetic gains from a breeding system based on inbred lines and the seed production benefits from a sexual propagation system are too large to ignore. We call on leaders of public and private organizations to come together to explore the feasibility of this radical and exciting new strategy in potato breeding.

. 2004. Nitrogen use efficiency characteristics of commercial potato cultivars. Can. J. Plant Sci. 84: 589-598. One approach for reducing the contribution of potato (Solanum tuberosum L.) production to nitrate contamination of groundwater is to develop cultivars which utilize N more efficiently. In this study, variation in N use efficiency (NUE; dry matter production per unit crop N supply) characteristics of 20 commercial potato cultivars of North American and European origin were evaluated in 2 yr. Cultivars were grown with or without application of 100 kg N ha -1 as ammonium nitrate banded at planting. The recommended within-row spacing was used for each cultivar and no irrigation was applied. Plant dry matter and N accumulation were determined prior to significant leaf senescence. Crop N supply was estimated as fertilizer N applied plus soil inorganic N measured at planting plus apparent net soil N mineralization. Nitrogen use efficiency decreased curvilinearly with increasing crop N supply. Nitrogen use efficiency was lower for early-maturing cultivars compared to mid-season and late-maturing cultivars. A curvilinear relationship was obtained between plant dry matter accumulation and plant N accumulation using data for all cultivars. Deviations from this relationship were interpreted as variation in N utilization efficiency (NUtE; dry matter accumulation per unit N accumulation). Significant differences in NUtE were measured among cultivars of similar maturity. Nitrogen uptake efficiency (NUpE; plant N content per unit crop N supply) and soil nitrate concentration measured at plant harvest were uniformly low for all cultivars when crop N supply was limited, but varied among cultivars when N was more abundant. This suggests that potato cultivars vary more in terms of N uptake capacity (plant N accumulation in the presence of an abundant N supply) than in terms of NUpE. Les variétés ont été cultivées avec ou sans application latérale de 100 kg de N par hectare sous forme de nitrate d'ammonium. Les auteurs ont respecté l'écartement recommandé pour chaque cultivar et n'ont pas irrigué la culture. Ils ont déterminé la quantité de matière sèche dans la plante et l'accumulation de N avant une trop forte sénescence des feuilles. La quantité de N fournie aux plantes a été estimée à partir de l'engrais appliqué et de la concentration de N minéral dans le sol à la plantation, plus la minéral-isation nette apparente de cet élément. L'efficacité de l'assimilation de l'azote diminue de façon curviligne avec la hausse de la quantité de N disponible. Les cultivars hâtifs assimilent moins bien l'azote que les cultivars de mi-saison ou tardifs. Lorsqu'on analyse les données venant des différents cultivars, on remarque une relation curviligne entre la quantité de matière sèche et celle de N accumulées par la plante. Les écarts à cette relation sont attribués à une variation dans l'efficacité de l'assimilation du N (EAsN; accumulation de matière sèche par unité de N accumulée). L'EAsN présente d'importantes variations entre le...

Tuber eye depth of the potato (Solanum tuberosum L.) is an important trait for the processing quality and appearance of potatoes. In the present study, we used a cultivated diploid potato family (12601) of 107 plants to dissect the mode of inheritance and to map the gene(s) controlling the trait. The family segregated for both eye depth (deep vs shallow) and tuber shape (round vs long) traits. The deep eye (Eyd) phenotype was found to be associated with round tubers (Ro) in most progeny clones. Further evaluation of this population with molecular markers including simple sequence repeats, amplified fragment length polymorphism, and sequence-characterized amplified regions revealed that the primary locus for eye depth is located on chromosome 10. This map location was confirmed by evaluating a second diploid family (12586). The results of this study led to the following conclusions: (1) there is a major locus controlling the eye depth trait; (2) deep eye (Eyd) is dominant to shallow (eyd); (3) the Eyd/eyd locus is located on chromosome 10; and (4) the Eyd/eyd locus is closely linked with the major locus for tuber shape (Ro/ro), at a distance of about 4 cM.

The potato R locus is necessary for the production of red pelargonidin-based anthocyanin pigments in any tissue of the plant, including tuber skin and flower petals. The production of pelargonidins in plants requires the activity of dihydroflavonol 4-reductase (DFR) to catalyze the reduction of dihydrokaempferol into leucopelargonidin. To test the hypothesis that potato R encodes DFR, portions of both dfr alleles were sequenced from a diploid potato clone known to be heterozygous Rr. Sequence comparison revealed a polymorphic BamHI restriction site. The presence or absence of this site was monitored in three diploid populations that segregated for R, as well as in a wide range of tetraploid breeding clones and cultivars, by amplifying a fragment of dfr and digesting the products with BamHI. An identically sized dfr restriction fragment lacking the BamHI site was present in all potato clones that produced red anthocyanin pigments, while the same fragment was absent in many potato clones with white tuber skin and flowers. An independent RFLP test using DraI to detect sequence polymorphism was performed on a subset of the potato clones. This test also revealed dfr-derived bands that were present in all red-colored potatoes and absent in several white clones. The presence of shared restriction fragments in all red-colored potatoes provides strong evidence that R does indeed code for DFR. The data are also consistent with a 48 year-old hypothesis by Dodds and Long, that R was selected just once during the domestication of potato. A cDNA clone corresponding to the red allele of dfr was sequenced and compared to two other alleles. The red allele is predicted to encode a 382 amino acid protein that differs at ten amino acid positions from the gene products of the two alternative alleles. Several of these differences map in a region known to influence DFR substrate specificity in Gerbera.

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