Basic aspects of potato breeding via the diploid level

In this thesis research is presented on all steps in a potato breeding program via the diploid level: dihaploid induction, selection at the diploid level and sexual polyploidization. In spite of the significant seed parent x pollinator interaction estimated, IVP 101 was found to have a significant higher dihaploid induction ability than the widely used pollinators IVP 35 and IVP 48. Significant differences in dihaploid production ability between seed parents were also found. Dihaploid populations from 31 varieties or breeding lines were evaluated for occurrence and frequency of mutant phenotypes, for tuberization, flowering, pollen stainability, 2n-pollen production and resistance to Ro-1. The expression of yield, yield components, vine maturity, under water weight and chip colour at the diploid and tetraploid level and the parental effects on these characters of 4x . 2x progenies were investigated to find an answer to the question whether at the diploid level other selection criteria should be employed than at the tetraploid level when selecting tetraploid breeding lines. For yield direct selection at the diploid level had no effect on the performance of tetraploid progeny. For under water weight more stringent and for vine maturity less stringent selection criteria were required at the diploid level than at the tetraploid level. The frequently reported superiority of FDR 2n-gametes versus SDR 2n-gametes could be confirmed for yield only. For vine maturity, under water weight and chip colour no considerable differences were found between means of FDR and SDR progenies from reciprocal 4x-2x crosses

Pyramiding of Meloidogyne hapla resistance genes in potato does not result in an increase of resistance

High levels of resistance against Meloidogyne hapla have been identified in wild species of tuber-bearing potatoes, but only QTL with partial effects have been identified so far in back crosses with cultivated potato. This study was designed to test if pyramiding of two previously identified resistance genes, R Mh-tar and R Mh-chc A, will result in improved or even an absolute level of resistance. R Mh-tar and R Mh-chc A introgressed from the wild tuber-bearing potato species Solanum tarijense and Solanum chacoense were combined in a segregating diploid Solanum tuberosum population. With the aid of AFLP markers, descendants from this segregating population were classified into four groups, carrying no R gene, with only R Mh-tar , with only R Mh-chc A and a group with the pyramided R Mh-tar and R Mh-chc A. Upon inoculation with M. hapla isolate Bovensmilde, the group containing only R Mh-chc A showed a decline of 88% in average number of developed egg masses compared to the group without R Mh-chc A and R Mh-tar . The group of genotypes containing only R Mh-tar , but not R Mh-chc A, showed a decline of 55% in the number of developed egg masses compared to the group without R Mh-chc A and R Mh-tar . Unfortunately, the latter effect of R Mh-tar was not significant. The effect of both loci, R Mh-tar and R Mh-chc A combined, did not further reduce the number of egg masses compared to the level of R Mh-chc A alon

Towards F1 Hybrid Seed Potato Breeding

Compared to other major food crops, progress in potato yield as the result of breeding efforts is very slow. Genetic gains cannot be fixed in potato due to obligatory out-breeding. Overcoming inbreeding depression using diploid self-compatible clones should enable to replace the current method of out-breeding and clonal propagation into an F1 hybrid system with true seeds. This idea is not new, but has long been considered unrealistic. Severe inbreeding depression and self-incompatibility in diploid germplasm have hitherto blocked the development of inbred lines. Back-crossing with a homozygous progenitor with the Sli gene which inhibits gametophytic self-incompatibility gave self-compatible offspring from elite material from our diploid breeding programme. We demonstrate that homozygous fixation of donor alleles is possible, with simultaneous improvement of tuber shape and tuber size grading of the recipient inbred line. These results provide proof of principle for F1 hybrid potato breeding. The technical and economic perspectives are unprecedented as these will enable the development of new products with combinations of useful traits for all stakeholders in the potato chain. In addition, the hybrid’s seeds are produced by crossings, rendering the production and voluminous transport of potato seed tubers redundant as it can be replaced by direct sowing or the use of healthy mini-tubers, raised in greenhouses

Societal Costs of Late Blight in Potato and Prospects of Durable Resistance Through Cisgenic Modification

In the European Union almost 6 Mha of potatoes are grown representing a value of close to ¿6,000,000,000. Late blight caused by Phytophthora infestans causes annual losses (costs of control and damage) estimated at more than ¿1,000,000,000. Chemical control is under pressure as late blight becomes increasingly aggressive and there is societal resistance against the use of environmentally unfriendly chemicals. Breeding programmes have not been able to markedly increase the level of resistance of current potato varieties. New scientific approaches may yield genetically modified marker-free potato varieties (either trans- and/or cisgenic, the latter signifying the use of indigenous resistance genes) as improved variants of currently used varieties showing far greater levels of resistance. There are strong scientific investments needed to develop such improved varieties but these varieties will have great economic and environmental impact. Here we present an approach, based on (cisgenic) resistance genes that will enhance the impact. It consists of five themes: the detection of R-genes in the wild potato gene pool and their function related to the various aspects in the infection route and reproduction of the late blight causing pathogen; cloning of natural R-genes and transforming cassettes of single or multiple (cisgenic) R-genes into existing varieties with proven adaptation to improve their value for consumers; selection of true to the wild type and resistant genotypes with similar qualities as the original variety; spatial and temporal resistance management research of late blight of the cisgenic genetically modified (GM) varieties that contain different cassettes of R-genes to avoid breaking of resistance and reduce build-up of epidemics; communication and interaction with all relevant stakeholders in society and transparency in what research is doing. One of the main challenges is to explain the different nature and possible biological improvement and legislative repercussions of cisgenic GM-crops in comparison with transgenic GM-crops. It is important to realize that the present EU Directive 2001/18/EC on GM crops does not make a difference between trans- and cisgenes. These rules were developed when only transgenic GM plants were around. We present a case arguing for an updating and refinement of these rules in order to place cisgenic GM-crops in another class of GM-plants as has been done in the past with (induced) mutation breeding and the use of protoplast fusion between crossable species. Keywords Cisgenesis - Cloning - Communication - Late blight - Phytophthora infestans - Potato - Resistance management - Selection - Transformatio

Participatory potato breeding model involving organic farmers and commercial breeding companies in the Netherladns

Organic farmers urgently need cultivars resistant to Phytophthora infestans. Such cultivars also need to be adapted to other traits important for organic farming systems. One goal in the first five years of this ten-year, public-private partnership was to establish a program within the Dutch potato breeding system that includes farmer breeders working in close collaboration with six commercial breeding companies and two research institutes. To meet the goals we have involved 14 organic farmer breeders through setting up a yearly breeding course. A pre-breeding program is now running to introgress late blight resistance from wild relatives into cultivated material, and to make crossings with advances genitors to distribute seeds to farmer and commercial breeders for selection. In this paper a short overview is given of the results of 2009-2013

Basic aspects of potato breeding via the diploid level

In this thesis research is presented on all steps in a potato breeding program via the diploid level: dihaploid induction, selection at the diploid level and sexual polyploidization. In spite of the significant seed parent x pollinator interaction estimated, IVP 101 was found to have a significant higher dihaploid induction ability than the widely used pollinators IVP 35 and IVP 48. Significant differences in dihaploid production ability between seed parents were also found. Dihaploid populations from 31 varieties or breeding lines were evaluated for occurrence and frequency of mutant phenotypes, for tuberization, flowering, pollen stainability, 2n-pollen production and resistance to Ro-1. The expression of yield, yield components, vine maturity, under water weight and chip colour at the diploid and tetraploid level and the parental effects on these characters of 4x . 2x progenies were investigated to find an answer to the question whether at the diploid level other selection criteria should be employed than at the tetraploid level when selecting tetraploid breeding lines. For yield direct selection at the diploid level had no effect on the performance of tetraploid progeny. For under water weight more stringent and for vine maturity less stringent selection criteria were required at the diploid level than at the tetraploid level. The frequently reported superiority of FDR 2n-gametes versus SDR 2n-gametes could be confirmed for yield only. For vine maturity, under water weight and chip colour no considerable differences were found between means of FDR and SDR progenies from reciprocal 4x-2x crosses

Peditree: Pedigree Database Analysis and Visualization for Breeding and Science

At the Wageningen Laboratory of Plant Breeding, a software package has been developed to query a simple structured database with variety pedigree data. The package, called Peditree, creates a tree-shaped representation of pedigree information and has several visualization and lookup options. Estimates of inbreeding coefficient within a pedigree or coefficients of coancestry among pedigrees can be obtained. Furthermore trait data -if available- can be linked, displayed within the pedigree tree, and used to highlight pedigree entries that comply with set criteri