ABSTRACT
Data on the production of tetraploid hybrid plants after electrofusion of protoplasts from various diploid (2n = 2x =24) Solarium tuberosum and S. phureja are reported. Ten different fusion combinations were used. Six hybrids with the tetraploid chromosome number 2n=4x=48 were tested under field conditions for their performance in various agronomic traits (tuber type, tuber yield, underwater weight of tubers, numbers of tubers, mean weight per tuber). Tuber yield in five of the six hybrid clones was similar to that of cv Bintje. One hybrid clone (35-4) had three times higher tuber yield than cv Bintje. The mean tuber weight of this hybrid was similar to that of cv Bintje. The results of this study prove that fertile tetraploid somatic hybrids having similar or higher tuber yield than that of cv Bintje can be obtained through somatic hybridization. This technique is now included in commercial potato breeding programs in The Netherlands.
ABSTRACT
The microsporogenesis of three somatic hybrids of potato, i.e. one tetraploid Solanum tuberosum (+) S. phureja, one tetraploid and one hypertetraploid S. tuberosum (+) desynaptic mutant, has been examined and compared with the microsporogenesis of the di(ha) ploid fusion partners. The somatic hybrids had a first meiotic division with uni-, bi-, and multivalents like that of tetraploid potatoes, illustrating introgression and dominance over desynapsis. Abnormal spindle orientations at second meiotic division, sporad types with reduced and unreduced cells and viable pollen occurred at various frequencies. Pollen fertility could not be predicted on the basis of pollen fertility of the fusion partners. Pollen sterility was partially due to abnormal chromosome numbers. Only the tetraploid S. tuberosum (+) desynaptic mutant produced normal amounts of viable seeds.
ABSTRACT
Crossability between the diploid species S. circaeifolium subsp. circaeifolium (crc) and other diploid species, primarily diploid S. tuberosum subsp. tuberosum (tbr-2x), was studied. Forty-seven hybrids were obtained from crosses between crc as female parent and tbr-2x and some other species from series Tuberosa as male parents. Of these hybrids 17% were diploids; the other 83% were triploids, probably carrying two genomes of crc. Female fertility was sufficient to obtain offspring from backcrosses with the cultivated parent. Pollen stainability of the f1 varied, and micro-pollen as well as unreduced pollen occurred. During meiosis of the diploids and triploids a rather high proportion of univalents was found, and in the triploids on average two or three trivalents per cell were found. All hybrids were resistant to Globodera pallida pathotypes 2 and 3, and 75% of the tested genotypes were highly resistant to Phytophthora infestans. Solanidine, tomatidine, tomatidenol, and demissidine glycosides were found in tubers of the hybrids. Comparisons with somatic hybrids between crc and tbr-2x are made. It is concluded that crc is a valuable Solanum species that can and should be included in potato breeding programs.
ABSTRACT
Somatic fusions between the cultivated potato Solanum tuberosum and the wild species S. circaeifolium subsp. circaeifolium Bitter were produced in order to incorporate desirable traits into the potato gene pool. Selection of the putative hybrids was based on a difference in callus morphology between the hybrids and their parents, with the hybrids showing typical purple-colored cells in otherwise green calli. In all, 17 individual calli regenerated to plants. Of the nine plants that could be transferred to the greenhouse, eight showed a hybrid and one a parental morphology. Restriction fragment length polymorphism (RFLP) analysis confirmed the hybrid character in the former group. Chloroplast counts in stomatal guard cells and flow cytometric determination of nuclear DNA content showed that four hybrid plants were tetraploid (4x), one was mixoploid (5x-8x), and the others were polyploid (6x; 8x). Three out of four tetraploid hybrids were found to be fully resistant to Phytophthora infestans, and all four hybrids were resistant to Globodera pallida pathotypes Pa2 and Pa3. It was further observed that the type and amount of steroidal glycoalkaloids varied among the tubers of the parents and the hybrids. Using the hybrids as female parents in crosses with S. tuberosum, viable seeds could be obtained. This demonstrates the potential of these hybrids in practical plant breeding.