Knowledge on the genetic variation of populations of Bemisia tabaci (Genn.) can improve the understanding of genetic diversity found in their biotypes and, consequently, offer guidelines for its management. In this study, the molecular characterization was performed and genetic diversity data were obtained for this insect from three regions of Brazil on different crops [cotton and soybean (Mato Grosso - MT); cabbage (Distrito Federal - DF); soybean and potato (São Paulo - SP)], using RAPD markers. RAPD analysis indicated 80.6% polymorphic loci and the average genetic similarity obtained by the Jaccard coefficient was 0.67. The whitefly populations collected on potato (SP) and soybean (MT) had higher genetic diversity values (0.75 and 0.72, respectively). Shannon's index (Ho) showed higher values for potato and soybean (SP e MT), and a smaller value for cabbage (DF). A high genetic divergence within and among the collected populations occurred, structured according to the regions of collection. Moreover, the great genetic similarity observed between potato (SP) and soybean (SP) populations suggested that both belong to the same biotype B and reinforces the polyphagous behavior of the species.

Knowledge on the genetic variation of populations of Bemisia tabaci (Genn.) can improve the understanding of genetic diversity found in their biotypes and, consequently, offer guidelines for its management. In this study, the molecular characterization was performed and genetic diversity data were obtained for this insect from three regions of Brazil on different crops [cotton and soybean (Mato Grosso - MT); cabbage (Distrito Federal - DF); soybean and potato (São Paulo - SP)], using RAPD markers. RAPD analysis indicated 80.6% polymorphic loci and the average genetic similarity obtained by the Jaccard coefficient was 0.67. The whitefly populations collected on potato (SP) and soybean (MT) had higher genetic diversity values (0.75 and 0.72, respectively). Shannon's index (Ho) showed higher values for potato and soybean (SP e MT), and a smaller value for cabbage (DF). A high genetic divergence within and among the collected populations occurred, structured according to the regions of collection. Moreover, the great genetic similarity observed between potato (SP) and soybean (SP) populations suggested that both belong to the same biotype B and reinforces the polyphagous behavior of the species.

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.

Premise of the study: Intron Targeting (IT) primers were developed for potato using expressed sequence tags (EST) and NCBI database records to study genetic diversity. METHODS: and Results: Twenty-nine polymorphic intron targeting (IT) markers were generated and characterized from 30 samples of potato and 22 samples of Solanum nigrum to detect polymorphism. The number of alleles (A) per locus ranged from 2 to 7 in the analyzed populations, and the observed heterozygosity (HO) and expected heterozygosity (HE) from 0 to 0.833 and 0.750, respectively. All of the primers also amplified in the related species S. nigrum. CONCLUSIONS: The developed markers will provide valuable tools for genetic diversity analysis, genetic mapping, and marker-assisted breeding of potato and related Solanum species.

In 2005, an extensive survey of bacterial wilt in Cameroon collected 110 strains of #Ralstonia solanacearum# from wilting tomato, potato, pepper, huckleberry (Solanum scabrum), sesame, and amaranth. The genetic diversity and phylogeny of selected strains from Cameroon were assessed by multiplex-polymerase chain reaction (PCR), race 3/biovar 2-specific PCR, and sequence analyses of the mutS and egl genes. These data were compared with those from 33 reference strains covering the known diversity within the R. solanacearum species complex. Strains isolated in Cameroon clustered into three of the four known phylotypes: I (Asian), II (American), and III (African). Lowland tomato strains belonged to phylotype I and were quite homogeneous. The strains belonging to phylotype II were genetically diverse, and partitioned into subclusters IIA and IIB (sequevar 1, race 3/biovar 2). Cameroon strains in the African phylotype III were distinct from reference strains from Zimbabwe or the Indian Ocean, highlighting the genetic diversity present within this phylotype. Strains from potatoes growing in the highlands of West Cameroon fell into both phylotypes II (race 3/biovar 2) and III. These phylotype II and III highland strains attacked both potato and tomato and could therefore pose an economic threat to potato and tomato crops throughout Central Africa. This is the first comprehensive report on the genetic diversity of #R. solanacearum# strains in Cameroon. (Résumé d'auteur)

The plant pathogenic soil-borne fungus Rhizoctonia solani causes severe damages in crops all around the world. Tubers of potato are frequently affected by R. solani leading to the downgrading of the production. Generally the isolates involved in the sclerotia occurring at the surface of the tuber are assigned to the anastomosis group (AG) 3 but a more precise characterization of the diversity of this deleterious group is needed to set up appropriate control strategies. The diversity of 73 French isolates from the mains potato seed production areas and 31 isolates originating from 9 other countries was assessed according to 3 molecular approaches. Three phylogenetic trees were built up based on the sequences of the internal transcribed spacer (ITS) region and the gene tef-1α as well as the comparison of 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 3 different AGs among our collection (60 AG 3, 8 AG 2-1 and 5 AG 5). Grouping of the isolates belonging to the same AG was confirmed by the sequencing of the gene tef-1α used for the first time to study the genetic diversity of R. solani. About 42 % of the ITS sequences and 73 % of the gene tef-1α sequences contained polymorphic sites where several nucleotides are possible, suggesting that the cells of R. solani strains contain several copies of ITS and gene tef-1α within the same nucleus or between different nuclei. Phylogenetic trees showed a greater genetic diversity within AGs in tef-1α 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 potato variety from which they were isolated and their genetic diversity. This important and under evaluated genetic diversity as the lack of population structure suggest important genetic mixings leading to a constant evolution within R. solani and could explain the difficulties to control it successfully.

The plant pathogenic soil-borne fungus Rhizoctonia solani causes severe damages in crops all around the world. Tubers of potato are frequently affected by R. solani leading to the downgrading of the production. Generally the isolates involved in the sclerotia occurring at the surface of the tuber are assigned to the anastomosis group (AG) 3 but a more precise characterization of the diversity of this deleterious group is needed to set up appropriate control strategies. The diversity of 73 French isolates from the mains potato seed production areas and 31 isolates originating from 9 other countries was assessed according to 3 molecular approaches. Three phylogenetic trees were built up based on the sequences of the internal transcribed spacer (ITS) region and the gene tef-1α as well as the comparison of 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 3 different AGs among our collection (60 AG 3, 8 AG 2-1 and 5 AG 5). Grouping of the isolates belonging to the same AG was confirmed by the sequencing of the gene tef-1α used for the first time to study the genetic diversity of R. solani. About 42 % of the ITS sequences and 73 % of the gene tef-1α sequences contained polymorphic sites where several nucleotides are possible, suggesting that the cells of R. solani strains contain several copies of ITS and gene tef-1α within the same nucleus or between different nuclei. Phylogenetic trees showed a greater genetic diversity within AGs in tef-1α 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 potato variety from which they were isolated and their genetic diversity. This important and under evaluated genetic diversity as the lack of population structure suggest important genetic mixings leading to a constant evolution within R. solani and could explain the difficulties to control it successfully.

Affiche, résumé<br/>Affiche, résumé | The plant pathogenic soil-borne fungus Rhizoctonia solani causes severe damages in crops all around the world. Tubers of potato are frequently affected by R. solani leading to the downgrading of the production. Generally the isolates involved in the sclerotia occurring at the surface of the tuber are assigned to the anastomosis group (AG) 3 but a more precise characterization of the diversity of this deleterious group is needed to set up appropriate control strategies. The diversity of 73 French isolates from the mains potato seed production areas and 31 isolates originating from 9 other countries was assessed according to 3 molecular approaches. Three phylogenetic trees were built up based on the sequences of the internal transcribed spacer (ITS) region and the gene tef-1α as well as the comparison of 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 3 different AGs among our collection (60 AG 3, 8 AG 2-1 and 5 AG 5). Grouping of the isolates belonging to the same AG was confirmed by the sequencing of the gene tef-1α used for the first time to study the genetic diversity of R. solani. About 42 % of the ITS sequences and 73 % of the gene tef-1α sequences contained polymorphic sites where several nucleotides are possible, suggesting that the cells of R. solani strains contain several copies of ITS and gene tef-1α within the same nucleus or between different nuclei. Phylogenetic trees showed a greater genetic diversity within AGs in tef-1α 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 potato variety from which they were isolated and their genetic diversity. This important and under evaluated genetic diversity as the lack of population structure suggest important genetic mixings leading to a constant evolution within R. solani and could explain the difficulties to control it successfully.

We assessed the geographic distribution, biovar, phylotype, DNA fingerprints (rep-PCR), and/or endoglucanase sequence of potato bacterial wilt pathogen, Ralstonia solanacearum (Rs), in Japan. Rs has been isolated from potato fields in southwestern, warm, temperate regions. Of the 188 isolates, 74 belonged to biovar N2 (39%), 44 to biovar 3 (24%), and 70 to biovar 4 (37%). Biovars N2 and 4 strains were widely distributed, from northern (Hokkaido) to southern (Okinawa) Japan. Based on the results of multiplex-PCR analysis, every potato strains belonged to either phylotype I or IV. Phylotype I comprised both biovars 3 and 4 strains. On the other hand, phylotype IV included biovar N2 strains. None of the strains belonged to phylotype II or III or biovar 1 or 2. Phylogenetic analysis based on DNA fingerprints and endoglucanase gene sequences clarified the genetic diversity of the Japanese potato strains and the close genetic relationship between the Japanese strains and the Asian strains in phylotypes I and IV.