Endosperm balance number manipulation for direct in vivo germplasm introgression to potato from a sexually isolated relative (Solanum commersonii Dun.)

Diploid (2n = 2x = 24) Solanum species with endosperm balance number (EBN) = 1 are sexually isolated from diploid 2EBN species and both tetraploid (2n = 4x = 48, 4EBN) and haploid (2n = 2x = 24, 2EBN) S. tuberosum Group Tuberosum. To sexually overcome these crossing barriers in the diploid species S. commersonii (1EBN), the manipulation of the EBN was accomplished by scaling up and down ploidy levels. Triploid F1 hybrids between an in vitro-doubled clone of S. commersonii (2n = 4x = 48, 2EBN) and diploid 2EBN clones were successfully used in 3x × 4x crosses with S. tuberosum Group Tuberosum, resulting in pentaploid/near pentaploid BC1 progenies. This provided evidence of 2n (3x) egg formation in the triploid female parents. Two selected BC1 pentaploid hybrids were successfully backcrossed both as male and as female parents with S. tuberosum Group Tuberosum. The somatic chromosome number varied greatly among the resulting BC2 progenies, which included hyperaneuploids, but also a number (4.8%) of 48-chromosome plants. The introgression of S. commersonii genomes was confirmed by the presence of S. commersonii-specific randomly amplified polymorphic DNA markers in the BC2 population analyzed. The results clearly demonstrate the feasibility of germplasm introgression from sexually isolated diploid 1EBN species into the 4x (4EBN) gene pool of the cultivated potato using sexual hybridization. Based on the amount and type of genetic variation generated, cumbersomeness, general applicability, costs, and other factors, it would be interesting to compare the approach reported here with other in vitro or in vivo, direct or indirect, approaches previously reported.

Transgenic potato (Solanum tuberosum) tubers synthesize the full spectrum of inulin molecules naturally occurring in globe artichoke (Cynara scolymus) roots

The ability to synthesize high molecular weight inulin was transferred to potato plants via constitutive expression of the 1-SST (sucrose:sucrose 1-fructosyltransferase) and the 1-FFT (fructan: fructan 1-fructosyltransferase) genes of globe artichoke (Cynara scolymus). The fructan pattern of tubers from transgenic potato plants represents the full spectrum of inulin molecules present in artichoke roots as shown by high-performance anion exchange chromatography, as well as size exclusion chromatography. These results demonstrate in planta that the enzymes sucrose:sucrose 1-fructosyltransferase and fructan:fructan 1-fructosyltransferase are sufficient to synthesize inulin molecules of all chain lengths naturally occurring in a given plant species. Inulin made up 5% of the dry weight of transgenic tubers, and a low level of fructan production also was observed in fully expanded leaves. Although inulin accumulation did not influence the sucrose concentration in leaves or tubers, a reduction in starch content occurred in transgenic tubers, indicating that inulin synthesis did not increase the storage capacity of the tubers.