In this study, RAPD and pedigree data were used to investigate the genetic relationships in a group of 45 diploid hybrid potato clones used in the breeding and genetics program of the Agriculture and Agri-Food Canada Potato Research Centre in Fredericton, New Brunswick, and used for the potato after-cooking darkness program at the Nova Scotia Agricultural College. These hybrids were derived from crossing primitive cultivated South American diploid species such as Solanum phureja or Solanum stenotomum and wild diploid species such as Solanum chacoense and other wild Argentine species with haploids of Solanum tuberosum. These hybrids have subsequently undergone up to 30 years of breeding and selection, for adaptation to local growing and storage conditions, processing traits and pest resistances. The objectives of this study were to estimate the level of genetic similarity (GS) among these sets of clones and to investigate the correlation between RAPD-based GS and f, based on pedigree information. Genetic similarity coefficients varied from 0.29 to 0.90 with a mean of 0.65 when based on the RAPD data, whereas the coefficient of parentage varied from zero to 0.75 with a mean of 0.11. The degree of relationship between the similarity matrices based on RAPD and pedigree was measured by comparing the similarity matrices with the normalized Mantel test. A low positive correlation (R = 0.104, p = 0.999) between the two matrices was observed. Cluster analysis using GS divided the clones into many subgroups that did not correspond well with the grouping based on pedigree. The level of genetic variation present in this set of potato clones is very high. Rigorous selection pressure aimed at different breeding purposes may result in the genetic differentiation of the clones from the same origin.

Sixteen Swedish PCN populations (nine Globodera rostochiensis and seven G. pallida populations) were compared with 20 other European populations (nine G. rostochiensis and 11 G. pallida populations) from Germany, the Netherlands, Norway and the United Kingdom in an AFLP study. Seven AFLP primer combinations were used to amplify genomic DNAs extracted from cysts. A dendrogram, based on UPGMA and evaluated by bootstrap analysis, contained two main clusters, one for each species. The Swedish Ro1 populations were very similar to corresponding populations from other parts of Europe. Remaining G. rostochiensis populations appeared as a genetically heterogeneous group with two Swedish populations being most dissimilar. Within G. pallida there was strong support for differentiating Pa1 populations from Pa2/3 populations. All Swedish G. pallida populations were grouped in the Pa2/3 cluster, and there were indications that they might have two main European origins. On the whole, the study indicates that there is considerable heterogeneity in Swedish PCN populations, justifying the maintenance of effective phytosanitary regulations.

This series of monographs intends to draw attention to a number of species which have been neglected in a varying degree by researchers or have been underutilized economically. It is hoped that the information compiled will contribute to: (1) identifying constraints in and possible solutions to the use of the crops, (2) identifying possible untapped genetic diversity for breeding and crop improvement programmes and (3) detecting existing gaps in available conservation and use approaches. Mashua (Tropaeolum tuberosum R. & P.), along with several potato species (Solanum spp.), ulluco (Ullucus tuberosus Caldas) and oca (Oxalis tuberosa Molina), pertains to the group of edible tuber crops indigenous to the cool-temperate Andes. Mashua is economically much less important than the other Andean tuber crops, but, as this monograph is intended to show, the crop's potential has been largely overlooked and opportunities for wider use within its native range and beyond have remained unexplored (Fano and Benavides 1992; Hermann and Heller 1997). Mashua contributes to tuber diversity, resulting in greater production stability in the heterogeneous Andean environments.

The population structure of Phytophthora infestans in the Toluca Valley of central Mexico was assessed using 170 isolates collected from cultivated potatoes and the native wild Solanum spp., S. demissum and S. xendinense. All isolates were analyzed for mitochondrial DNA (mtDNA) haplotype and amplified fragment length polymorphism (AFLP) multi-locus fingerprint genotype. Isolate samples were monomorphic for mtDNA haplotype because all isolates tested were of the Ia haplotype. A total of 158 multilocus AFLP genotypes were identified among the 170 P. infestans isolates included in this study. P. infestans populations sampled in the Toluca Valley in 1997 were highly variable and almost every single isolate represented a unique genotype based on the analysis of 165 AFLP marker loci. Populations of P. infestans collected from the commercial potato-growing region in the valley, the subsistence potato production area along the slopes of the Nevado de Toluca, and the native Solanum spp. on the forested slopes of the volcano showed a high degree of genetic diversity. The number of polymorphic loci varied from 20.0 to 62.4% for isolates collected from the field station and wild Solanum spp. On average, 81.8% (135) of the AFLP loci were polymorphic. Hetero-zygosity varied between 7.7 and 19.4%. Significant differentiation was found at the population level between strains originating from cultivated potatoes and wild Solanum spp. (P = 0.001 to 0.022). Private alleles were observed in individual isolates collected from all three populations, with numbers of unique dominant alleles varying from 9 to 16 for isolates collected from commercial potato crops and native Solanum spp., respectively. Four AFLP markers were exclusively found present in isolates collected from S. demissum. Indirect estimation of gene flow between populations indicated restricted gene flow between both P. infestans populations from cultivated potatoes and wild Solanum hosts. There was no evidence found for the presence of substructuring at the subpopulation (field) level. We hypothesize that population differentiation and genetic isolation of P. infestans in the Toluca Valley is driven by host-specific factors (i.e., R-genes) widely distributed in wild Solanum spp. and random genetic drift.

This series of monographs intends to draw attention to a number of species which have been neglected in a varying degree by researchers or have been underutilized economically. It is hoped that the information compiled will contribute to: (1) identifying constraints in and possible solutions to the use of the crops, (2) identifying possible untapped genetic diversity for breeding and crop improvement programmes and (3) detecting existing gaps in available conservation and use approaches. Mashua (Tropaeolum tuberosum R. & P.), along with several potato species (Solanum spp.), ulluco (Ullucus tuberosus Caldas) and oca (Oxalis tuberosa Molina), pertains to the group of edible tuber crops indigenous to the cool-temperate Andes. Mashua is economically much less important than the other Andean tuber crops, but, as this monograph is intended to show, the crop's potential has been largely overlooked and opportunities for wider use within its native range and beyond have remained unexplored (Fano and Benavides 1992; Hermann and Heller 1997). Mashua contributes to tuber diversity, resulting in greater production stability in the heterogeneous Andean environments | A. Grau, R.O. Dueñas, C.N. Cabrera, M. Hermann, 'Mashua: Tropaeolum tuberosum Ruíz & Pav', p.55, 2003

Ploidy manipulations consist on scaling up and down chromosome numbers of a species within a polyploid series. Chromosome sets are manipulated with haploids, 2n gametes, and through interspecific-interploidy crosses. Analytical breeding schemes rely mainly on ploidy manipulations to “capture” diversity from exotic (wild or non-adapted germplasm) and use 2n gametes to incorporate this genetic diversity through unilateral (USP; n x 2n or 2n x n) or bilateral (BSP; 2n x 2n) polyploidization. Most interesting examples of analytical breeding in crop improvement are in vegetatively propagated species such as potato, sweetpotato, cassava, among roots and tubers, and plantain/banana among fruit crops. This breeding approach appears promising in blackberry, blueberry, strawberry and other fruits. An evolutionary crop breeding method was developed for further improvement of the plantain genome. This method ensued from the genetic knowledge accumulated during the analytical breeding of this triploid (3x) crop. Heterozygous 3x landraces are crossed with diploid (2x) wild or cultivated accessions showing the desired characteristic(s). Primary tetraploid (4x) hybrids are recovered after USP, i.e., 2n eggs from 3x x n pollen from 2x. Secondary triploids result by crossing selected 4x with selected 2x stocks, both producing n gametes. Triploid Musa hybrids may also occur due to USP among 2x, i.e., one 2x producing 2n gametes. Hybrids may result from artificial hand-pollination or through polycrosses among selected 4x and 2x parents according to their specific combining ability. Synthetic populations derived from the polycrosses may be tested in other locations to identify promising offspring for cultivar selection. Local selections may lead to dynamic conservation of genetic resources because farmers will preserve distinct locally adapted, improved genotypes across environments. Analytical breeding, coupled with this evolutionary breeding approach, offers an option for broadening the genetic base of fruit crops, enhancing their adaptation, and sustaining breeding gains in respective gene pools.

The common potato, Solanum tuberosum spp. tuberosum (tbr), is a tetraploid species with a narrow genetic base, but with a large number of related species that harbor great genetic diversity for numerous characters of agronomic interest. S. kurtzianum (ktz) and S. ruiz-lealii (rzl) are wild diploid relatives with potential resistance to adverse biotic and abiotic factors. To evaluate if this wild germplasm can be incorporated by conventional crosses into the tbr gene pool, pollen-pistil compatibility relations and seed set in interspecific crosses with tbr were investigated. In 4x tbr x 2x ktz crosses and the reciprocals, 89% and 52.2% of genotypic combinations (respectively) were compatible at the pollen-pistil level. Seeds were obtained from some genotypic combinations in both directions of the cross, suggesting that functional 2n gametes might be produced by particular ktz genotypes. In 2x rzl x 4x tbr crosses and their reciprocals, 35% and 11.7% (respectively) of the genotypic combinations were compatible at the pollen-pistil level, but no seeds were obtained. These results indicate that the reproductive isolation between 4x tbr and 2x ktz is incomplete, and that gene exchange between them is feasible. Moreover, further studies will have to be carried out with rzl to ascertain its crossability with 4x tbr.

The objective of this work was to look at the variability between isolates of the three fungal species, Colletotrichum gloeosporioides, Fusarium solani and Phoma caricae-papayae associated with stem-end rot in papaya fruits (Carica papaya L.) which were produced in different regions of Brazil. In one trial, comparisons were made considering morphological and cultural characteristics exhibited by the fungi grown in different media: Potato dextrose agar (PDA), Papaya extract agar (PEA) and Czapek. In general, mycelial growth of all fungi was higher in PDA and PEA and no correlation was seen between growth rates and other morphocultural characteristics such as color, colony type and others for all isolates compared. The analysis of AFLP markers revealed that there is a huge genetic variation between isolates as demonstrated by the production of 339 bands in eletrophoretic gel. With basis on genetic diversity it was possible to characterize four groups of C. gloeosporioides, F.solani and P. caricae-papayae. No correlation was seen between morphocultural characteristics and AFLP analysis. | Objetivou-se, com este trabalho, verificar a variabilidade morfocultural e genética de fungos associados à podridão peduncular do mamão (Carica papaya L.). As avaliações morfoculturais foram feitas pelo índice de crescimento micelial e características das colônias, como coloração e tipo de micélio, quando os isolados foram crescidos em diferentes meios de cultura (BDA, MDA e Czapek). A variabilidade genética foi verificada por meio de análises de AFLP. Os isolamentos foram feitos em frutos obtidos de diferentes regiões produtoras do Brasil. Foram estudados oito isolados de cada uma das três espécies mais incidentes (Colletotrichum gloeosporioides, Phoma caricae-papayae e Fusarium solani). Foi verificado que os meios BDA e MDA promoveram um maior e mais rápido crescimento micelial para a maioria dos isolados testados e houve variações nas colorações das colônias desses isolados nos diferentes meios. A análise de AFLP gerou um total de 339 bandas polimórficas, indicando uma variabilidade genética entre os isolados de cada espécie fúngica, com alguns desses microrganismos formando grupos divergentes dos demais. Não foi observada uma correlação entre características morfológicas e análises de AFLP.

<jats:title>Abstract</jats:title><jats:p>Asexual organisms that naturally coexist with sexual relatives may hold the key to understanding the maintenance of sex and recombination, a long‐standing problem in evolutionary biology. This situation applies to the peach‐potato aphid, <jats:italic>Myzus persicae</jats:italic>, in southeastern Australia where cyclical parthenogens form mixed populations with obligate parthenogens. We collected <jats:italic>M. persicae</jats:italic> from several areas across Victoria, genotyped them at seven microsatellite loci and experimentally determined their reproductive mode. The geographic distribution of reproductive modes was correlated with two environmental variables that differentially affect obligate and cyclical parthenogens; obligate parthenogens were less frequent in areas with cold winters because they cannot produce frost‐resistant eggs while cyclical parthenogens were limited by the availability of their primary host, peach, on which sexual reproduction takes place. Clonal diversity increased with the proportion of cyclical parthenogens in a sample because they tended to have unique microsatellite genotypes, whereas many obligate parthenogens were copies of the same genotype. Two obligately asexual genotypes stood out as being very abundant and widespread, one constituting 24% and the other 17.4% of the entire collection. Both of these highly successful genotypes were present in the majority of all collection sites. Genetic population structure was weak, albeit significant, with a multilocus <jats:italic>F</jats:italic><jats:sub>ST</jats:sub> of only 0.021 when samples were reduced to only one representative of each genotype. Interestingly, obligate parthenogens were, on average, more heterozygous and exhibited larger allele size differences between the two alleles at individual loci than cyclical parthenogens. This striking pattern could result from hybridization, for which we have no evidence, or may reflect the previously proposed model of biased mutational divergence of microsatellite alleles within asexual aphid lineages.</jats:p> | Christoph Vorburger, Melanie Lancaster, Paul Sunnucks