Department of Agriculture, Wageningen University, 6708 PB Wageningen, THE NETHERLANDS.
Glycoalkaloids are secondary metabolites that are characterised by an undesirable taste, and which are known to be toxic when consumed in large quantities. Some wild potato germplasms that are used for the introgression of genes encoding heat tolerance contain high concentrations of glycoalkaloids in the tubers. However, heat tolerance is not necessarily associated with high glycoalkaloid content in the tubers and it is feasible to detect heat tolerant clones that will not accumulate excessive glycoalkaloid levels in the tubers when exposed to heat stress. Breeding and selection should therefore take place to lower the glycoalkaloid content in potato tubers and DNA markers can significantly facilitate the selection process.
The main objective of this study was to develop DNA markers associated with total glycoalkaloid (TGA) content in the potato tubers. For this purpose two tetraploid resource populations segregating for TGA-content were constructed and analysed in two consecutive experiments. The populations were characterised for the genetic control of total glycoalkaloid content in the tubers. Although tuber glycoalkaloid content was the most important trait under study, additional agronomic and morphological traits were also recorded and analysed. These additional traits were used to characterise the phenotypic and genetic architectures of the two segregating populations used in this study.
In both populations, the parental clones differed markedly in TGA-content and the progeny population was normally distributed for this trait after logarithmic transformation. Broad sense heritability estimate of TGA-content was 0.54 in Cara Å~ LT7 and 0.50 in NT8 Å~ LT7 and the trait proved to be inherited in a non-dominant manner. The minimum number of genes contributing to TGA-content was estimated to be between 3 and 7. None of the other traits recorded in this study showed a statistically significant genetic association with TGA-content. This suggests that tuber TGA-content may be genetically modulated without any significant adverse effects on other agronomic traits. Broad sense heritability was estimated for all traits assessed. Heritability estimates that were similar in both populations ranged from 0.1 for the number of main stems to 0.5 for total tuber glycoalkaloid content. In both populations, most heritabilities estimated were about 0.3. Main agronomic traits, such as tuber dormancy, tuber weight, and maturity, appeared to be controlled by several additive genes.
Three hundred and forty-two Inter-Simple Sequence Repeat (ISSR) single primers or two such primer combinations were used to amplify random PCR products. Two single ISSR markers were found significantly associated with TGA-content. A multiple regression analysis was also carried out using a ‘stepwise’ procedure. In this analysis TGA-content was the dependent variable whereas the polymorphic PCR products and all possible two-way interactions among them were the independent variables. The resulting best model consisted of an interaction between two loci in addition to a single locus effect. This interaction suggests that the expression of TGA-content is partially modulated by two interacting loci.
A single copy DNA marker for a morphological leaf characteristic, vein depth, was generated in a study of the association of molecular markers with morphological characteristics. ISSR primers were used to generate random PCR products followed by the design of a CAPS marker. A multiple regression analysis showed that the best model consisted of the ISSR-PCR product and a CAPS-PCR product. The results suggest that these products represent separate alleles at the same DNA locus. Vein depth is apparently controlled by one or several genes that modulate the lamina expansion, either during cell division or during cell elongation. Vein depth is shown to be regulated in an additive way and hence allelic differences are supposedly accountable for small differences in lamina growth. In this study, the feasible generation of a single copy DNA marker in tetraploids and its possible use in the study of tetrasomic inheritance are demonstrated.
Progress has been made in the development of a DNA marker associated with TGA-content in potato tubers. When the development of such DNA marker will be completed, it may be valuable in programmes which include the introgression of genes from wild species while discarding genotypes high in TGA-content, contributing considerably to breeding potatoes adapted to warm climates.