Subclonal variation and skin russeting in potato, (Solanum tuberosum L.)

Abstract

Selection of subclonal variants for improved characters is an accepted method of potato cultivar improvement. These variants are similar to a commercially acceptable cultivar, but possess one or more unique characters such as russeting or increased vine vigor which can make them more acceptable or better adapted than the original cultivar. While these subclonal variants have been observed and selected for clonal propagation for years, their origin has yet to be explained. A two year study of subclonal selection for putative russet skin mutations of 'Century Russet' was conducted in Texas and Colorado to improve the russeting character in 'Century Russet'. RAPD analysis of a segregating F I family derived from a russet x white cross and of three sets of russet/nonrusset near-isogenic lines was conducted to identify a marker(s) for the russeting gene(s) to help explain the origin of subclonal variants for the russeting trait. RAPD analysis was also used to attempt to fingerprint subclones, or strains, of 'Russet Norkotah' selected for improved vine vigor for use as genetic evidence for Plant Variety Protection. Location did affect russeting, with Texas producing darker russeted tubers. Differences between years was not significant. Two Hunter spectrocolorimeter instruments were used to quantify degrees of russeting. The A-value scale of the spectrocolorimeters was the best single predictor of visual russet rankings. After using morphological characters to eliminate non-'Century Russet' types, 18 of the remaining selections were darker than the 'Century Russet' control, and 5 selections were significantly lighter. Although 8% of the 2527 bands scored in the F I progeny from the russet x white cross were polymorphic, none of these suggested linkage to the russeting gene(s). Of these, 5.8% were estimated to be repeatable based on a subsample which was repeated four times. An average of nine bands per primer were produced. No polymorphic bands were identified in any of the russet/non-russet near-isogenic lines. An average of nine bands per primer were produced for 'Russet Norkotah' and its three subclones, but none of the 2966 bands scored were polymorphic.