Selection of monoploids for protoplast fusion and generation of intermonoploid somatic hybrids of potato

Abstract

The union of potato monoploid genotypes (2n=1x =12) through protoplast fusion may result in vigorous somatic hybrids due to a reduction of the genetic load normally present in this highly heterozygous tetraploid (2n=4x=48) crop. More than 100 androgenic monoploids derived from diploid (2n=2x=24) Solanum phureja Juz. & Buk. and S. chacoense Bitt. x S. phureja clones were evaluated in field trials during 1996 and 1997 to identify the most promising genotypes for protoplast fusion experiments. Compared to the total population, the 1996 selected genotypes had higher means for tuber number (30.1 vs 11.2 tubers/plant), average tuber weight (3.0 vs 1.8 g/tuber) and total yield (66.1 vs 20.4 g/plant). Similarly, the 1997 selected genotypes had higher means for tuber number (42.8 vs 25.4 tubers/plant), average tuber weight (3.6 vs 2.5 g/tuber) and total yield (114.0 vs 63.4 g/plant) compared to the total population. The 31 selected monoploid genotypes from 1996-97 varied in their response to protoplast isolation and culture from no growth (9), cell enlargement (5), limited cellular divisions (8), callus formation (5) to plant regeneration from callus (4). Chemical fusion and electrofusion produced three groups of intermonoploid somatic hybrids. Polymorphic simple sequence repeat (SSR) loci enabled distinction of somatic hybrids from parental somaclones. Rapid DNA extraction with SSR analysis enabled screening of calluses to identify somatic hybrid tissue prior to plant regeneration. The somatic hybrids were highly polyploid, mostly hexaploid (2n=6x=72), possibly due to fusion of endopolyploid protoplasts and/or chromosomal doubling during plant regeneration.