This study aimed to evaluate the genetic diversity and identify potato cultivars by RAPD and SSR markers. The genomic DNA of 16 potato cultivars was amplified with 25 RAPD primers that generated 92 polymorphic bands and 20 SSR primer pairs that produced 136 polymorphic bands. The dendrograms generated by cluster analysis distinguished the cultivars genetically although the dendrograms were not correlated in the comparison of the two markers used. The PIC values demonstrated the high information content of the primers used and 16 potato varieties were identified based on six RAPD primers and three SSR primer pairs. Thus, by means of RAPD and SSR markers the genetic diversity was assessed and the 16 commercial potato cultivars analyzed in this study were identified.

In the United States, two sweet potato begomoviruses, sweet potato leaf curl virus (SPLCV) and sweet potato leaf curl Georgia virus (SPLCGV), were previously identified in Louisiana. In recent years, at least seven additional sweet potato begomoviruses have been identified in other parts of the world. In an effort to determine the genetic diversity and distribution of sweet potato begomoviruses in the U.S., we focused our efforts on molecular characterization of field-collected begomovirus isolates in two states: Mississippi and South Carolina. Using rolling-circle amplification, a total of 52 clones of the full genome were obtained. Initial inspection of alignments of the end sequences in these clones revealed a strong genetic diversity. Overall, 10 genotypes could be assigned. A majority of the isolates (50/52) in eight genotypes were shown to be closely related to SPLCV. A representative clone of each genotype was fully sequenced and analyzed. Among them, four genotypes from South Carolina with 91-92% sequence identity to the type member of SPLCV were considered a new strain, whereas four other genotypes from Mississippi with >95% sequence identity to SPLCV were considered variants. In addition, a member of a proposed new begomovirus species was identified after comparative sequence analysis of the isolate [US:SC:646B-9] from South Carolina with less than 89% sequence identity to any known begomovirus. Hence, the provisional name Sweet potato leaf curl South Carolina virus (SPLCSCV) is proposed. Moreover, a natural recombinant consisting of two distinct parental genomic sequences from SPLCV and SPLCGV was identified in the sample [US:MS:1B-3] from Mississippi. Two recombinant breakpoints were identified, one in the origin of replication and the other between C2 and C4. This knowledge about the genetic diversity of begomoviruses infecting sweet potato will likely have a major impact on PCR-based virus detection and on disease management practice through breeding for virus resistance.

Genetic variability of Potato virus Y (PVY) isolates infecting potato has been characterized but little is known about genetic diversity of PVY isolates infecting tobacco crops. In this study, PVY isolates were collected from major tobacco-growing areas in China and single-lesion isolates were produced by serial inoculation on Chenopodium amaranticolor. Most isolates (88%) caused systemic veinal necrosis symptoms in tobacco. Of these, 16 isolates contained a PVYO-like coat protein (CP) and PVYN-like helper component proteinase (HC-pro) and, in this respect, were similar to the PVYN-Wi, PVYN:O, and PVY-HN2 isolates characterized from potato in Europe, the United States, and China, respectively; two isolates contained a PVYO-like HC-pro and a PVYN-like CP; another two isolates had recombination junctions in the CP-encoding region. Both the HC-pro and CP of PVY were under negative selection as a whole; however, seven amino acids in HC-pro and six amino acids in CP were under positive selection. Selection pressures differed between the subpopulations of PVY distinguished by phylogenetic analysis of HC-pro and CP sequences. When PVY isolates from potato were included, no host-specific clustering of the PVY isolates was observed in phylogenetic and nucleotide diversity analyses, suggesting frequent spread of PVY isolates between potato and tobacco crops in the field.

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699 | International audience | The soilborne fungus Rhizoctonia solani is a pathogen of many plants and causes severe damage in crops around the world. Strains of R. solani from the anastomosis group (AG) 3 attack potatoes, leading to great yield losses and to the downgrading of production. The study of the genetic diversity of the strains of R. solani in France allows the structure of the populations to be determined and adapted control strategies against this pathogen to be established. The diversity of 73 French strains isolated from tubers grown in the main potato seed production areas and 31 strains isolated in nine other countries was assessed by phylogenetic analyses of (i) the internal transcribed spacer sequences (ITS1 and ITS2) of ribosomal RNA (rRNA), (ii) a part of the gene tef-1a and (iii) the total DNA fingerprints of each strain established by amplified fragment length polymorphism (AFLP). The determination of the AGs of R. solani based on the sequencing of the ITS region showed three different AGs among our collection (60 AG 3 PT, 8 AG 2-1 and 5 AG 5). Grouping of the strains belonging to the same AG was confirmed by sequencing of the gene tef-1a used for the first time to study the genetic diversity of R. solani. About 42% of ITS sequences and 72% of tef-1a sequences contained polymorphic sites, suggesting that the cells of R. solani strains contain several copies of ITS and the tef-1a gene within the same nucleus or between different nuclei. Phylogenetic trees showed a greater genetic diversity within AGs in tef-1a sequences than in ITS sequences. The AFLP analyses showed an even greater diversity among the strains demonstrating that the French strains of R. solani isolated from potatoes were not a clonal population. Moreover there was no relationship between the geographical origins of the strains or the variety from which they were isolated and their genetic diversity.

In Florida, air-potato is an invasive weed with high management priority, which may soon be targeted using classical biological control. This yam was introduced during the early 20th century by the United States Department of Agriculture (USDA) from areas throughout its extensive range. Our objectives were to characterize the genetic diversity of the invasive population in Florida and to identify the source regions of introduction. Authorities have often asserted the African provenance of the species in Florida, but our analyses, conducted using chloroplast markers, indicate that Florida air-potato is more similar to specimens examined from China than to those from Africa. Low intraspecific genetic diversity in Florida indicates that the invasive population was the result of at least two introductions becoming established in Florida.

International potato germplasm (Solanum tuberosum L.) has been long introduced to and bred in Kenya and the accumulated Kenyan Solanum germplasm is unique in its geographical and climatic ranges of adaptation to tropical highlands. However, little is known about the genetic diversity of these improved Solanum accessions. A representative set of 48 potato accessions grouped as farmer varieties, local genotypes and modern varieties was selected and studied using the simple sequence repeat (SSR) technique. Twenty-two SSR primer pairs were applied and 122 polymorphic bands were scored. The frequencies of polymorphic bands ranged from 0.02 to 0.98 and averaged 0.35. The proportion of total SSR variation occurring among four origin categories (International Potato Centre (CIP), Europe, Kenya and Unknown) of accessions was 6.32%; between accessions introduced before and after 1980 4.79%; and among three germplasm classes of accessions 4.36%. Accessions from the CIP displayed more SSR variation than those from Europe. More SSR variation was detected in the accessions introduced/bred after 1980. The modern varieties displayed slightly more diversity than the farmer varieties and local genotypes. Some dominant groups of accessions largely from CIP and Europe were found, but these groups were not distantly separated. Both the genetically most distinct accessions and the possibly genetically related accessions were identified. These results not only demonstrate the considerable genetic variation harbored in the Kenyan potato germplasm, but also are significant for developing effective strategies of acquiring genetically diverse germplasm and for selecting genetically distinct potato materials to widen the Kenyan improved gene pool.

This thesis aims to fill the gap of information on the potato landrace diversity present in farmer fields of Ecuador. Passport data from previous collections (1970’s and 1980’s) were used to identify Carchi, Chimborazo and Loja as representative areas of potato diversity. The status of on-farm conservation in these three selected areas is covered in Chapter 2. Microsatellites (SSRs) helped us to describe the genetic relationships among the landraces found in these areas (Chapter 3). The characterization of potato landraces with respect to late blight resistance (Chapter 4) and quality traits (Chapter 5) complement the description. Previous reports suggested loss of potato diversity (genetic erosion) in Ecuadorian farmer fields, but our collection of a total of 174 landraces showed that these areas still hold a substantial amount of potato landrace diversity (Chapter 2). More potato landraces were found in Chimborazo and Loja than previously sampled in the 70’s and 80’s. A comparison between the two collections, in each of the three areas, indicated only a small overlap in landrace names suggesting that the sampling of local landraces was far from exhaustive, both during the 70’s and 80’s and during the present collection trips. This is further supported by the fact that the diversity fair, which was organized after our collection trips in Chimborazo, resulted in many new landraces. Surveys and farmer meetings in the study areas were used to describe the landrace-holders and the characteristics of the farming system they use. Mostly elderly people and small-scale farmers are currently maintaining potato landraces. These farmers look for income alternatives besides agriculture, resulting in migration. The vulnerability of the potato conservation varies among our study areas. In Carchi younger farmers demonstrate a lack of interest in cropping potato landraces. In Loja farming is not seen as the only sustainable source of income and there is a perceived lack of support from the government for the activities necessary to maintain local landraces. In Chimborazo farmers are culturally more attached to their land and see agriculture as a family activity, rendering the potato landrace conservation less vulnerable. Externally driven on-farm conservation interventions, such as diversity fairs or re-introduction of landraces, were highly appreciated by the farmers and could help to conserve the potatoes. Diploid, triploid and tetraploid potato landraces are found in farmers fields. The material sampled at the three areas shows a high allelic diversity. At the tetraploid level (the most abundant) this was comparable to the variation present in an European collection of more than 800 varieties. More alleles are expected to be found when more material from other areas will be screened. There was no clear grouping of material collected according to study region, suggesting extensive movement of seed potatoes all over Ecuador. A comparison of the application of variety names with the genetic relationships among potato landraces can result in either under- or over-estimation of the variability present in farmer fields (Chapter 3). In a number of cases landraces with identical common names proved to be genetically different or individual collection samples were actually a mixture of two landraces, pointing at under-estimation of diversity present. On the other hand, cases that might lead to over-estimation were also evident, e.g. genetically identical material was present under different names. Our sampling of genetically different landraces for late blight (LB) resistance characterization (Chapter 4) confirmed that there was some variation for this trait among the landraces. Most of the landraces were susceptible to moderately resistant, but also some landraces with field resistance were identified. The observed field resistance was comparable to that in the widespread improved variety Fripapa. Possible strategies to improve late blight resistance in potato in Ecuador could include the identification of accessions with resistance among the local landraces, although only a few accessions may be expected to present field resistance. The introduction of new sources of resistance from other origins is a more viable alternative. One could attempt to introduce novel R-genes in material that already contains some level of quantitative resistance. We found varying levels of dry matter, total polyphenol and total carotenoid contents among Ecuadorian potato landraces, some were comparable to the improved varieties. Based on the dry matter content most of the Ecuadorian landraces evaluated were suitable for processing as French fries or chips. The total polyphenol content of these potatoes were quite similar to those reported by the International Potato Center (Peru) for a set of accessions representing more than 60% of the variability in their potato collection. The total carotenoid content values of the Ecuadorian potatoes included in our study were similar or lower compared to previous studies on improved or Andean potatoes. The identified outstanding potato materials could be used to develop new potato varieties through plant breeding. In Chimborazo and Loja farmers select landraces mainly based on their nutritional characteristics. However, in Carchi farmers prefer commercial improved varieties. Farmers´ preferences include empirical valuation of potato-quality rather than specific knowledge on nutritional characteristics of these potatoes. This thesis provides important knowledge about the potato landraces in Ecuador. Our results can serve as the basis for further description and use of Ecuadorian native potatoes by breeders and local communities.