Maurício Rossato

The Host Status Of Coffee (Coffea arabica) To Ralstonia solanacearum Phylotype I Isolates

The Solanaceae and Rubiaceae families have close phylogenetic relationship, being members of the same Asterid clade of Eudicots. Species of the Solanaceae family are among the most important hosts for Ralstonia solanacearum (Rs), the causal agent of the bacterial wilt disease. In the present work, we investigated the potential host status of the genus Coffea to a diverse collection of Rs isolates. Pathogenicity tests were carried out under greenhouse conditions with nine Rs isolates from distinct geographic areas and host plants. Seedlings of three coffee (Coffea arabica) cultivars were inoculated via root dipping into a bacterial suspension. Plants of all cultivars were infected with three out of nine Rs isolates. Xylem vessels were colonized and plants developed typical wilt symptoms, although milder when compared with tomato seedlings used as controls. All isolates pathogenic to coffee were classified as phylotype I (previously race 1/biovar3). This finding, together with the remarkable pathogen plasticity, the reallocation of the coffee agricultural frontier to warm climate areas, and the current global warming trend are major driving forces of a stronger selection pressure towards Rs isolates pathogenic to coffee trees under natural conditions.

Evaluation of Solanum peruvianum (sensu lato) germplasm to a standard Ralstonia solanacearum race 1/biovar 1 isolate and to a novel ‘Hawaii 7996’ resistance-overcoming race 3/biovar 2A isolate from Brazil

A major strategy to control the bacterial wilt (BW), caused by the Ralstonia species complex in tomato has been the employment of resistant cultivars and/or root-stocks. The tomato line ‘Hawaii 7996’ is a major source of stable and broad-spectrum resistance against BW. However, the detection of R. solanacearum isolates that overcome the ‘Hawaii 7996’ resistance in Brazil and elsewhere highlights the need for preemptive breeding actions. In the present work, 72 accessions of Solanum peruvianum (sensu lato) and other four wild species were evaluated against two R. solanacearum isolates: ‘CNPH-RS 488’ (race 3/biovar 2A/phylotype II/sequevar 1), virulent on ‘Hawaii 7996’, and ‘CNPH-RS 489’ (race 1/biovar 1/phylotype IIA/sequevar 50), a standard isolate that is avirulent on Hawaii 7996′. The responses to inoculation of the tested accessions were compared to that of ‘Hawaii 7996’ and ‘L390’ (BW-susceptible). The clear-cut differences in the responses among accessions to both isolates suggested the presence of distinct BW resistance mechanisms in this germplasm. Sixteen accessions displayed resistant reactions to ‘CNPH-RS 488’ and 31 to ‘CNPH-RS 489’. However, only seven accessions (predominantly of the species S. corneliomulleri) displayed resistance reactions to both isolates. These new sources of resistance to R. solanacearum may be useful for breeding programs aiming to anticipate potential problems with the further dissemination of bacterial populations with a virulence profile similar to that of R. solanacearum ‘CNPH-RS 488’.

Breeding potatoes for resistance to bacterial blight in Brazil: a quick review in face of a more effective screening protocol.

Abstract Bacterial wilt (BW), caused by Ralstonia solanacearum , is one of the most important diseases of potato ( Solanum tuberosum subsp. tuberosum ) in Brazil and the main cause of rejection of fields for tuber seed certification. Genetic resistance is not a feasible control currently since no commercially-appealing BW resistant cultivars are available. The development of resistant cultivars is challenging due to the genetic complexity of resistance, pathogen variability, lack of resistance sources in the species, and the tetraploid background of the crop. In addition, to date, only field selection has been effective in identifying stable resistance in progenies derived from crosses involving resistant wild relatives. Field selection is laborious and demands uniformly infested fields. After many years of germplasm breeding, we succeeded in developing two resistant clones, MB-03 and MB9846-01, both producing tubers with rather reasonable characteristics. These clones are being crossed with elite genotypes. To speed up progeny evaluation, we developed a straightforward screening protocol in greenhouse conditions, based on selection at the seedling stage. The methodology is presented and discussed here. Briefly, the early selection was very effective to screen a large number of seedlings in a rather short period of time. It considerably increased the rates of selection of resistant clones in the field when compared to selection directly in the field, without the prior greenhouse seedling stage. Nevertheless, field selection remains crucial for confirming resistance, testing for genotype-environment interaction and evaluating agronomic and tuber characteristics. Among the resistant clones previously identified in our program, progenies of clone MB9846-01 resulted in higher selection indexes in the field (BW resistance + tuber characteristics) than those of clone MB-03 when both clones were crossed with the susceptible cultivar Baraka. We adjusted the protocol to allow screening around 5,000 seedlings per year, counting with eight part-time workers, four in the laboratory/screenhouse and four in the field in critical periods. Keywords: Ralstonia solanacearum , Solanum tuberosum ssp. tuberosum , greenhouse screening, early selection, selection rates, germplasm breeding

Complete Genome Sequences of Sweet potato feathery mottle virus and Sweet potato virus G from Brazil

ABSTRACT In Brazil, Potyvirus species in sweet potatoes have been detected mostly by serology. Here, we report the complete genome sequences of two Potyvirus species, Sweet potato feathery mottle virus strain (SPFMV-UNB-01) and Sweet potato virus G strain (SPVG-UNB-01).

Relationships among Brazilian and worldwide isolates of Fusarium oxysporum f. sp. lactucae race 1 inferred from ribosomal intergenic spacer (IGS-rDNA) region and EF-1α gene sequences

Fusarium wilt, caused by Fusarium oxysporum f. sp. lactucae (FOLac), is amongst the main diseases affecting lettuce in subtropical regions. Although nationwide surveys indicated the exclusive presence of FOLac race 1 in Brazil, no detailed studies are available providing molecular evidences if these isolates were introduced into the country via contaminated seeds or if they are endemic populations. The translation elongation factor 1α (EF-1α) gene and rDNA intergenic spacer (IGS-rDNA) region represent the most comprehensive databases for comparative analyses of Fusarium isolates. Our aim was to assess the genetic relationships of 23 Brazilian FOLac race 1 isolates with a collection of FOLac isolates of worldwide origin, using the information from these genomic regions. A consistent single-cluster pattern was observed for FOLac race 1 isolates from Brazil, California-USA, Arizona-USA, Japan, Italy, as well as the novel FOLac race 4 isolates from the Netherlands based upon the EF-1α (604 nucleotides) and the IGS-rDNA (1859 nucleotides) sequences. Our analysis (based upon six single nucleotide polymorphisms identified only in the IGS-rDNA sequence) allowed the identification of intra-race 1 variation with the discrimination of four haplotypes. Isolates from Brazil, Italy, and a subset from the USA were classified into a single haplotype. The low diversity levels and the presence of only a single haplotype across the entire country are strong indications that Brazilian FOLac race 1 isolates are result of recent introduction event(s). This fast and widespread distribution of FOLac race 1 in Brazil has occurred more likely via importation and planting of contaminated seeds.