Somaclonal variation in tuber disc-derived populations of potato. II. Differential effect of genotype.

Three somaclonal populations of potato (Solanum tuberosum L.), each comprised of at least 1,000 plants, were regenerated from the cultivars Kennebec, Russet Burbank, and Superior. The frequency of formation of adventitious meristems from tuber disc explants varied significantly between these potato genotypes. Only 1.0-1.3% of each somaclonal population exhibited morphological aberrations. Regenerated populations of 'Kennebec' and 'Superior', when compared to respective control populations over three asexual generations, were similarly enriched with somaclones having more elongated tubers, a higher total tuber number and weight, a higher cull tuber number and weight, and earlier maturity. Somaclones of 'Russet Burbank' also produced more elongated tubers, a higher total tuber number, and a higher cull tuber number and weight but, in contrast, these somaclones were lower in total tuber weight, lower in U.S. 1 tuber number and weight, shorter in stem length, and lower in vigor. Of the three cultivars, 'Russet Burbank' somaclones possessed the greatest variability for most traits. Besides this significant genotype effect, quantitative traits differed amongst each other in respect of relative changes resulting from somaclonal variation. Observed differences among genotypes and quantitative traits will undoubtedly affect the success or failure of plant improvement programs attempting to utilize somaclonal variation.

Somaclonal variation in tuber disc-derived populations of potato : I. Evidence of genetic stability across tuber generations and diverse locations.

Approximately 1,600 potato (Solanum tuberosum L.) plants of the cultivar 'Superior' were regeneratedin vitro from meristems adventitiously initiated on tuber disc expiants. Direct regeneration from tuber disc cells, by passing a callus intermediary, is efficient and results in low frequencies of plants with gross phenotypic aberrations. The somaclonal plant population was statistically characterized in field plots over five asexual generations and in three diverse locations. When compared in advanced generations to a large population of control plants propagated from stem cuttings, the means of the somaclonal population were significantly different, often shifted in the desirable direction, for 16 of 22 horticulturally important traits. Somaclonal population variances statistically exceeded those of the controls for 13 of the 22 traits. Regressions between consecutive tuber generations and between locations or replications (blocks) within a generation were significant in the somaclonal population for all traits analyzed. In a few instances, significant control population regressions occurred that are interpreted to be the result of non-random, non-genetic factors primarily affecting control plants of low vigor. Selected somaclones exhibiting desirable alterations for yield, tuber number and shape, and vigor were stable over more than two consecutive asexual generations.