ANALYSIS OF SOMATIC HYBRIDS BETWEEN 2 STERILE DIHAPLOID SOLANUM-TUBEROSUM L BREEDING LINES - RESTORATION OF FERTILITY AND COMPLEMENTATION OF GLOBODERA-PALLIDA PA2 AND PA3 RESISTANCE

Fourteen somatic hybrids generated by electrofusion of mesophyll proto plasts from a non-flowering dihaploid S. tuberosum clone, DHAK-11, and a male-sterile dihaploid clone S. tuberosum, DHAK-33, were grown in t he greenhouse and subjected to morphological assessments and tests for fertility and resistance to the white potato cyst nematode Globodera pallida pathotypes Pa2 and Pa3. The ploidy level of the hybrids ranged from 38 to 63 chromosomes. All hybrids developed flowers with violet petals except for one, hy-56, that possessed red petals. The colour of the tuber skin was purple in all hybrids except in hy-56 where the tu ber skin was red. All of the hybrids were female fertile and generated viable seeds. Near-tetraploid hybrids produced the highest number of seeds per fruit and these seeds had a normal size. Hybrids with 58 or more chromosomes produced smaller seeds and less seeds per fruit. The germination frequency of the seeds was not influenced by the chromosom e number of the hybrids. Pollen viability was determined and the male fertility of three hybrids was tested. Pollination with these three hy brids gave rise to fruit development, but only one produced viable see ds. The hybrids were tested for resistance to G. pallida pathotypes Pa 2 and Pa3. A high level of resistance to Pa3, inherited from one paren tal clone, DHAK-11, and a high level of resistance to Pa2, inherited f rom the other parental clone, DHAK-33, was combined in four hybrids. T hese results demonstrate, that protoplast fusion is an efficient metho d for restoring the fertility of somatic hybrids generated from steril e parent clones, and is a powerful procedure for the complementation o f multigenetic disease resistance traits in potato breeding lines.