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

Phenotypic analyses of multi-environment data for two diverse tetraploid potato collections: comparing an academic panel with an industrial panel

Phenotypic analyses of two different association panels of tetraploid potato cultivars are presented. Association panels are sets of variously related genotypes assembled for association analysis purposes. The aims of this research were to inspect, analyse and compare two phenotypic data sets, a first step in association mapping analysis. A first panel of 205 contemporary and historical cultivars, selected to represent the commercial potato germplasm pool, was evaluated in two trials in 2006, one on sandy soil and the other on clay soil, both with two replications. It was called the academic panel. Data for the second panel with 299 genotypes were compiled from contributions from five breeding companies and included 66 locations and 18 years. Each of the participating breeding companies contributed data from their clonal selection programmes for 38 advanced breeding clones and a series of standard cultivars. It was called the industrial panel. Variance components for genotypic main effects and genotype-by-environment interactions were calculated, and estimates for the random genotypic main effects were produced. The genotypic main effects for 19 agro-morphological and quality traits were used to study trait by trait correlations within each panel. In addition, for the genotypes shared by both panels, the correlation of genetic main effects between the panels was investigated. The heritability of all traits was high and no large differences were observed between panels. Coefficients of trait variation were highly correlated (r¿=¿0.9) for both panels and trait by trait correlations in both panels showed highly similar patterns. These results demonstrate that a single-year balanced field trial as well as using breeders’ records yields robust phenotypic information that can be used in a genome-wide association study. Issues related to data management and definition of traits are discussed

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

Localisation of morphological traits on the genetic map of potato using RFLP and isozyme markers = [Localisatie van morfologische eigenschappen op de genetische kaart van de aardappel door middel van RFLP en isozym merkers]

The thesis describes the construction of a genetic linkage map of the potato genome, comprising molecular, isozyme and morphological markers. The linkage map is based on the offspring from non-inbred parents. The computer program JOINMAPallowed to combine the maternal and paternal linkage groups, which are a consequence of using non-inbred parents. The map was applied for the analysis and localisation of morphological and agronomically important traits, with special emphasis on the inheritance of anthocyanin pigmentation. The presence of multiple alleles was demonstrated at the Ro locus which harbours a QTL involved in tuber shape. The accurate analysis of quantitative genetic variation caused by the segregation of a QTL with multiple alleles requires molecular markers which can distinguish all possible four allele combinations

Comparing powder magnetization and transport critical current of Bi,Pb(2223) tapes

The magnetic field dependence of the critical current in (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10+x/ tapes is compared with the magnetization response of isolated grains extracted from the tapes. Special attention is paid to the low-field behavior. The goal of the experiment is to test the widely-used hypothesis that current paths in these tapes contain both weak- and strong- linked branches, which in low field act in parallel. The data agree with this hypothesis; at temperatures above 50 K the powder magnetization drops off exponentially from the self-field to the irreversibility field, while the transport and magnetization currents in the intact tapes show an extra low-field component. Below 50 K the powder behavior becomes less straightforward, but the parallel-path picture in the tapes still holds

Strain effects in high temperature superconductors investigated with magneto-optical imaging

In order to determine the influence of intermediate deformation steps on the mechanical behavior of Bi-based tapes, the effect of longitudinal applied strain is investigated by means of magneto-optical imaging. The strain is applied in a helium flow-cryostat. Cracks appear soon after the critical current in Bi-based tapes is degraded. All filaments form multiple cracks that grow into tape-wide cracks, running from one filament to the next. The crack location is not caused by stress concentrations in the matrix, but by the mechanically weak colony boundaries. Because of the absence of intermediate rolling steps in the production of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub x/ tapes, a different crack structure is observed compared to Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ tapes. The relation between the critical current and the formation of cracks is studied. The degradation in critical current before the critical strain is reached may be caused by microcracks that remain undetected by magneto-optical imaging. The influence of strain on the microstructure of YBa/sub 2/Cu/sub 3/O/sub x/ coated conductors is also investigated with magneto-optical imaging. The formation of cracks is believed to be determined by the nickel substrate and related to the Ni-grain size

Critical current versus strain research at the University of Twente

At the University of Twente a U-shaped spring has been used to investigate the mechanical properties of a large variety of superconducting tapes and wires. Several mechanisms are responsible for the degradation of critical current as a function of applied strain. A change in its intrinsic parameters causes a reversible critical current dependence in Nb3Sn. The critical current reaches a maximum at a wire-dependent tensile strain level, and decreases when this tensile strain is either released or further increased. In Bi-based tapes the critical current is virtually insensitive to tensile strain up to a sample-dependent irreversible strain limit. When this limit is exceeded, the critical current decreases steeply and irreversibly. This behaviour is attributed to microstructural damage to the filaments. This cracking of the filaments is verified by a magneto-optical strain experiment. Recent experiments suggest that in MgB2 the degradation of critical current is caused by a change in intrinsic properties and damage to the microstructure. Magneto-optical imaging can be used to investigate the influence of applied strain on the microstructure of MgB2, as is done successfully with Bi-based tapes. In all these conductors the thermal precompression of the filaments plays an important role. In Nb3Sn it determines the position of the maximum and in Bi-based and MgB2 conductors it is closely related to the irreversible strain limit