Effect of light exposure on the glycoalkaloid content of Solanum phureja tubers

The individual glycoalkaloid contents of tubers from eleven Solanum phureja genotypes have been determined prior to and following exposure to light. In all genotypes, light exposure resulted in a statistically significant increase in total glycoalkaloid content. In nine of the genotypes studied, this was not only due to an increase in the levels of the solanidine-based glycoalkaloids, alpha-solanine and alpha-chaconine, but also due to the light-induced synthesis of a tomatidenol-based glycoalkaloid, alpha-solamarine. Those genotypes that accumulated alpha-solamarine in their tubers also contained tomatidenol-based glycoalkaloids in their leaves, but only solanidine-based glycoalkaloids were detected in the sprouts.

Predictive correlates of shoot regeneration from potato protoplast culture

Adaptation of protoplast regeneration systems for use on untested or recalcitrant potato genotypes can be a time-consuming exercise. Callus growth and xylogenesis were evaluated as early correlates of shooting potential to shorten this process. Callus growth was of limited value for predicting organogenesis but a linear relationship was observed between xylogenesis and shooting frequency. Increases in xylem content above a minimum threshold corresponded with increases in shooting frequency. The predictive value of the relationship was tested using a simple protocol modification (the culture of calli on a filter paper base). Calli on filter paper produced more xylem elements and shoots than those plated directly on medium. The potential of xylem content as a predictive test of shooting frequency is discussed.

Use of seedling progeny tests for genetical studies as part of a potato (Solanum tuberosum subsp. tuberosum) breeding programme

A diallel set of crosses, including selfs and some reciprocal crosses, was made between 15 parents chosen for their male fertility from those included in a tetraploid potato (Solanum tuberosum subsp. tuberosum) breeding programme at the Scottish Crop Research Institute. Seedling progeny tests were used to evaluate the progenies for non-race-specific resistance to late blight (Phytophthora infestans) in both foliage and tubers, quantitative resistance to the white potato cystnematode (PCN) (Globodera pallida) and the commercial worth of their tubers as judged by breeders' visual preference. No reciprocal differences were found. Comparisons of the selfs and crosses revealed inbreeding depression for breeders' preference, which varied among the parents from negligible to severe, whilst there were also statistically significant differences for foliage and tuber blight, but not for PCN. When the selfs were omitted from the combining ability analyses, large differences in general combining ability (GCA) were found for all four traits, and smaller differences in specific combining ability for tuber blight and breeders' preference. The only statistically significant correlation between GCAs for different traits was a favourable one of r = 0.56 between foliage and tuber resistance to late blight. It was concluded that prospects were good for simultaneously improving all four traits by multitrait genotypic recurrent selection.

The use of cross prediction methods in a practical potato breeding programme

Most previous studies on cross prediction methods have examined relatively few crosses, particularly in relation to the numbers involved in most breeding programmes. In this paper the feasibility of using cross prediction methods was examined in a practical potato (Solanum tuberosum) breeding scheme by the analyses of progeny from 52 crosses. The variate considered was breeder's preference, a visual assessment made of the harvested tubers to estimate their commercial potential. The results showed that it was possible to identify the superior crosses. Cross prediction based simply on the mean preference scores, averaged over scorers and clones within progenies, estimated on seedlings or first clonal year plants, provided the best estimate of a progeny's performance in the third clonal generation. Predictions based on the expected proportion of clones that would transgress a given target value also provided a good indication of a progeny's potential. The poorest prediction was obtained by using the observed frequency of desirable clones in a progeny sample. The implications for potato breeding are discussed.