José Ricardo Pfeifer Silveira

Incidence of pectolytic erwinias associated with blackleg of potato in Rio Grande do Sul

Erwinia carotovora subsp. atroseptica (Eca), E. carotovora subsp. carotovora (Ecc) and E. chrysanthemi (Ech) may cause potato (Solanum tuberosum) blackleg. To determine the occurrence of these pathogens in the conditions found in the State of Rio Grande do Sul (RS), potato plants showing blackleg symptoms were harvested from 22 fields in nine counties in Serra do Nordeste, Planalto, Depressao Central, and Grandes Lagoas, from September to December of 1999 (Spring-Summer season). Green pepper (Capsicum annuum) fruits were used as a host to enrich for pectolytic erwinia from potato stems with blackleg symptoms. Bacteria were subsequently isolated on non-selective medium. Isolates that were Gram-negative, facultatively anaerobic, and pitted crystal-violet-pectate medium were tested for biochemical traits to identify the species and subspecies. Four hundred strains were identified as either Eca, Ecc or Ech. Although the three erwinias were found in RS potato fields, only three strains of Ech were found in one field. Frequencies of Eca and Ecc were 55 and 42%, respectively. Eight strains could not be assigned based on the biochemical characterization.

Diversidade genética e eficiência simbiótica de rizóbios noduladores de acácia-negra de solos do Rio Grande do Sul

Black wattle is the third most cultivated forest species in Brazil. Besides its economic importance, black wattle is also used to restore degraded areas, where soils are generally acid and Al levels high. This study intended to investigate the genetic diversity of indigenous rhizobia in soils in Rio Grande do Sul and to select isolates that fix N2 efficiently at low pH. Fifty Bradyrhizobium sp. isolates were obtained, which, along with the recommended strains BR 3067 and BR 3068, were molecularly characterized by PCR with primer BOX A 1-R. DNA band patterns of the isolates were used to construct a dendrogram by which the Shannon diversity index was calculated. Ten isolates were further tested for low pH tolerance and Al presence. Eight isolates were selected for a nitrogen-fixing greenhouse trial. High genetic diversity was observed among the isolates. Ten clusters were formed based on a 70 % similarity cut-off level and a diversity index of 4.3. The presence of Al did not affect the tested isolates, while growth decreased at pH 4.5. With respect to the symbiotic efficiency, T6-16 and V-7 were the most effective isolates, similar to the recommended strain BR 3068.

Eficiência de Trichoderma harzianum e Gliocladium viride na redução da incidência de Botrytis cinerea em tomateiro cultivado sob ambiente protegido

A producao de tomates no Estado do RS ocupa um importante papel socio-economico, que pode ser constatado pelo crescimento do cultivo dessa hortalica em ambiente protegido. Essa tecnica permite a producao de tomates em periodo de entressafra; no entanto, ocorrem tambem condicoes favoraveis para o desenvolvimento de doencas fungicas como o mofo cinzento provocado por Botrytis cinerea. O surgimento de racas de patogenos resistentes a fungicidas quimicos vem fazendo com que o controle biologico torne-se uma alternativa necessaria. Neste trabalho foi realizada selecao in vitro de 24 isolados do fungo Trichoderma harzianum e 12 de Gliocladium viride que inibiram o desenvolvimento do patogeno B. cinerea. Foram selecionados dois isolados (TRIC-30 e GLIO-10) para serem testados em experimentos em condicoes de campo com tomates cultivados sob ambiente protegido, nos quais a pulverizacao foliar semanal com uma suspensao com 2x107 conidios mL-1 reduziu significativamente a incidencia do mofo cinzento, enquanto a aplicacao dos antagonistas nas sementes, no substrato e na cova, no momento do plantio, nao reduziu a incidencia do patogeno.

Caracterização de estirpes de Ralstonia solanacearum isoladas de plantas de batata com murcha bacteriana, por PCR-Rep e RAPD

Considered one of the most important potato (Solanum tuberosum) pathogens in tropical and subtropical regions, as well as in temperate regions with warmer climate, Ralstonia solanacearum is a species with significant genetic diversity. It has been characterized in a binary system of races and biovars based on the range of host species and on the ability to use carbon sources. The attempts to use genetic resistance as a strategy to control R. solanacearum were shown to be unstable due to climatic changes in different regions and due to the variability of the pathogenic strains. Due to different epidemiological characteristics of the biovars, strains of biovar 2 are more likely to be eradicated in an integrated control system. In a survey performed in four regions where potato is produced in Rio Grande do Sul, isolates of R. solanacearum were obtained from 25 crop fields in ten municipalities. The biochemical analyses of the isolates revealed the occurrence of biovars 1 and 2, the latter being predominant. The isolates obtained were evaluated for their genetic variability by PCR, using repetitive sequences ERIC and BOX and random primers (RAPD). The PCR-ERIC and BOX were able to clearly differentiate the biovars 1 and 2. However, neither analysis was able to demonstrate variability among isolates of biovar 2 and only PCR-BOX showed some degree of variability among isolates of biovar 1. The amplification by RAPD demonstrates the distinction between the biovars and revealed that they show characteristic profiles that are closely related to the region where they were obtained.

Ocorrência das biovares 1 e 2 de Ralstonia solanacearum em lavouras de batata no estado do Rio Grande do Sul

Occurrence and distribution of biovars of Ralstonia solanacearum in the State of Rio Grande do Sul were assessed by harvesting potato (Solanum tuberosum) plants showing bacterial wilt symptoms in the spring of 1999. Plants were collected from 25 potato fields in ten counties in the four main production regions: Serra do Nordeste, Planalto Superior, Depressao Central and Grandes Lagoas. Species and biovar determinations were based on serological test with ELISA and the oxidative metabolism of sugars and alcohols. Ninety-four percent of 490 strains were identified as biovar 2. Occurrence of biovar 1 was recorded in Serra do Nordeste and Depressao Central. The incidence of biovars showed no correlation with local temperature or potato cultivars.

Epidemiological analysis of clones and cultivars of potato in soil naturally infested with Ralstonia solanacearum biovar 2

Os objetivos deste estudo foram avaliar o progresso da murcha bacteriana, a resistencia do clone MB 03, selecionado para a raca 1 em Brasilia, e detectar a presenca do patogeno em tuberculos colhidos de plantas assintomaticas. Durante a primavera (setembro a final de novembro no hemisferio sul) de 1999 e 2000, 14 cultivares ou clones foram cultivados num campo naturalmente infestado com R. solanacearum biovar 2, em Caxias do Sul, RS. O numero de plantas com sintomas de murcha foi registrado semanalmente para a obtencao da curva de progresso da doenca. Para comparar a resistencia dos genotipos de batata a murcha bacteriana foi calculada a area sob a curva de progresso da doenca. Dentre os modelos avaliados para ajuste das curvas, o modelo logistico foi o que melhor se ajustou. Ao final das avaliacoes, em cada periodo de cultivo, os tuberculos produzidos por plantas assintomaticas foram coletados e armazenados ate o inicio da brotacao, quando foram submetidos a testes para detectar a presenca de R. solanacearum. A cultivar Cruza 148 e o clone MB 03 foram os genotipos mais resistentes, mas ambos apresentaram tuberculos com infeccoes latentes. As implicacoes epidemiologicas da incidencia de R. solanacearum raca 3 em lavouras de batata, bem como da resistencia de determinados genotipos que podem propiciar tuberculos com infeccoes latentes, sao aspectos de importância para o manejo integrado da murcha bacteriana no RS.

Bradysia sp. em morangueiro

This paper describes the first record of Bradysia sp. (Insecta; Diptera; Sciaridae) in strawberry (Fragaria x ananassa), cultivated in the city of Eldorado do Sul, RS, Brazil. Strawberry was planted in plastic bags filled with a mixture of burnt rice hulls and peat and cultivated in a greenhouse. The presence of Bradysia sp was noticed in the second fortnight of August, 2005. The symptoms in strawberry and the probable consequences in terms of disease arising were described in the present study, as well as the morphological characterization of Bradysia sp. and its illustrations.

Caracterização da região espaçadora 16-23S rDNA para diferenciação de estirpes de rizóbios utilizadas na produção de inoculantes comerciais no Brasil

The identification of strains of rhizobia has been made by host specificity and regular microbiological tests. By forming a phylogenetically heterogeneous group, different molecular techniques have been employed to assist in the genetic characterization and identification of efficient and competitive strains for production of inoculants. This study aimed to characterize the spacer region 16S-23S rDNA of the strains of rhizobia used in commercial inoculants in Brazil for legume species, using PCR combined with RFLP, and assess the possibility of using this molecular marker as an auxiliary method for identification of strains. The amplification of the 16-23 S rDNA spacer region of rhizobium strains generated fragments with sizes ranging between 700 and 1350bp. Products from the amplification were subjected to digestion with Mps I, Dde I and Hae III endonucleases. The results indicated the possibility of using the technique of PCR-RFLP of 16S-23S spacer region rDNA as molecular marker to differentiate most strains tested and recommended for production of inoculants, in addition to the traditional microbiological techniques. However, this marker is not sufficiently discriminatory to be used in the identification of the strains recommended for the production of commercial inoculants.

Densidade populacional de Ralstonia solanacearum em cultivares de batata a campo

The occurrence of latent populations of Ralstonia solanacearum on potato (Solanum tuberosum) plants may represent inoculum source of unknown potential. Besides, it is also unknown if the latent population of the bacterium is lower in resistant than in susceptible cultivars. In order to study these points, an experiment was conducted in the field in two locations in Rio Grande do Sul State, Brazil. The objective was to verify the relationship between R. solanacearum population density and the potato cultivar resistance. The experiment was conducted in Eldorado do Sul, during the Spring, and in Caxias do Sul, during the Fall. Tubers of Achat, Baronesa, Elvira, Macaca, Monte Bonito, and Trapeira cultivars were inoculated with a R. solanacearum strain, biovar II, and planted in the field. Population density of the bacterium was estimated in the assymptomatic and wilted plants, by ELISA and imunofluorescence techniques. No evidence of relationship between population density of R. solanacearum and cultivar was found. Besides, the population density on Achat, known as the most resistant, one was similar to the other cultivars.

Incidence of Biovars 1 and 2 of Ralstonia solanacearum in Potato Fields at Rio Grande do Sul State, Brazil

Bacterial wilt caused by Ralstonia solanacearum is one of the most serious limitations to potato (Solanum tuberosum L.) crop at tropical, sub-tropical, and warmer areas of temperate zones of the world. R. solanacearum strains are grouped in races by host range and biovars according to their oxidative metabolism of sugars and alcohols. Strains of biovars 1 and 2 are able to infect potato. The first group has a wide host range, survives in the soil for long periods, and predominates in high temperature regions. The second one basically infects potato, occurs in temperate regions and presents higher incidence of latent infections. These different pathogen traits determine different measures on disease management. Biovar 2 is considered endemic in the South and Southeast regions of Brazil. Rio Grande do Sul State is located at South, latitude 28 to 34 and humid subtropical climate. Potato is grown yearly in two seasons, comprising an area larger than 48,000 ha, represented by at least four distinct production regions. The purpose of this research was to study the incidence and distribution of biovars 1 and 2 of R. solanacearum in those potato production regions.