RESUMO

ABSTRACT Some psyllids transmit 'Candidatus Liberibacter solanacearum' (Lso), the causal agent of devastating plant diseases of cultivated Solanaceae and Apiaceae. The recent detection of Bactericera cockerelli and Lso in Ecuador seriously threatens these crops in South America. There, neither the role of native psyllids in the Lso epidemiology nor the psyllid fauna of vegetables are known. With the aim to identify potential vectors and risk scenarios for the spread of Lso in South America, a survey of the psyllid fauna of Solanaceae and Apiaceae crops and associated weeds was conducted in Brazil. Samples were taken at 29 localities in four states. A total of 2857 specimens were sampled, representing at least 37 species of 23 genera and seven families. The most frequent species on carrot, chilli pepper and potato were Russelliana solanicola, R. capsici and Isogonoceraia divergipennis, respectively. Immatures of R. capsici were found on chilli pepper and of R. solanicola on carrot and potato, confirming these plants as hosts. The two psyllid species have been suspected previously to transmit plant pathogens of unknown identity. Russelliana solanicola is one of the few polyphagous species. Here the species is reported for the first time from carrot. Recent collections in Rio Grande do Sul suggest that Solanum laxum represents the original host of R. capsici, which subsequently shifted to chilli pepper. Both, adaptation to agricultural crops and the possibility of ability to transmit pathogens, make the two Russelliana species dangerous potential vectors of Lso and other plant pathogens in South America.

RESUMO

Maize striate mosaic virus (MSMV; genus Mastrevirus) was recently reported in maize plants in Brazil and also detected by metagenomic analyses in the corn leafhopper, Dalbulus maidis (DeLong & Wolcott). Although these findings suggested that D. maidis is a potential vector, no transmission studies have been performed. Here, we tested the transmission of MSMV by D. maidis from field-collected infected plants and plants infected with MSMV via leafhopper-mediated transmission in the laboratory; all plants were confirmed positive for MSMV by PCR. In each one of three transmission replicates, aviruliferous D. maidis nymphs and adults were confined together on a source plant during a 4-day acquisition access period (AAP) and subsequently transferred to healthy maize seedlings (10 individuals per test plant) in a series of 4-day inoculation access periods (IAPs). We also tested transmission by the corn aphid, Rhopalosiphum maidis (Fitch) and by mechanical inoculation of healthy maize seedlings. Only D. maidis transmitted MSMV, with overall transmission rates of 29.4 and 39.5% on field-collected infected plants and 18.5% on infected plants in laboratory. D. maidis transmitted MSMV until the third (8 to 12 days after the AAP) or fourth successive IAP (12 to 16 days), with gradual loss in transmission efficiency and rate of viruliferous insects over time, suggesting a persistent but nonpropagative mode of transmission. Infected test plants showed mottling symptoms with mild chlorotic streaks and height reduction. This is the first report of transmission of a mastrevirus by D. maidis, facilitating the completion of Koch's postulate for MSMV.

Assuntos

RESUMO

In Brazil, the host expansion of Xylella fastidiosa subsp. pauca was recently demonstrated with the report of diseased olive trees (Olea europaea), whose symptoms were associated with olive quick decline syndrome previously described in southern Italy. We employed both polymerase chain reaction-based techniques and culture medium isolation to investigate the geographic distribution of X. fastidiosa as well as the genetic signatures of 21 strains isolated from 11 olive orchards in both São Paulo and Minas Gerais States in Brazil. X. fastidiosa subsp. pauca was detected in 83% of the orchards examined in the region, and was positively diagnosed in 43.7% of all sampled plants with typical scorching symptoms. Of the 21 strains characterized with fast-evolving microsatellite (single sequence repeat [SSR]) markers, 20 different multilocus microsatellite genotypes were observed with the overall allelic diversity of HNei = 0.38. Principal component analysis using the SSR markers clustered all strains, except for three, in one cluster demonstrating a limited range of genetic diversity. Multilocus sequence typing analysis showed the prevalence of a sequence type (ST16) in 75% of the samples; three other novel STs (84, 85, and 86), were detected, all belonging to the X. fastidiosa subsp. pauca cluster. These results show that genetically diverse strains of X. fastidiosa subsp. pauca are widely present in olive orchards in southeastern Brazil, which is consistent with the long history of this bacterium in that region.

Assuntos

RESUMO

Homologous recombination affects the evolution of bacteria such as Xylella fastidiosa, a naturally competent plant pathogen that requires insect vectors for dispersal. This bacterial species is taxonomically divided into subspecies, with phylogenetic clusters within subspecies that are host specific. One subspecies, pauca, is primarily limited to South America, with the exception of recently reported strains in Europe and Costa Rica. Despite the economic importance of X. fastidiosa subsp. pauca in South America, little is known about its genetic diversity. Multilocus sequence typing (MLST) has previously identified six sequence types (ST) among plant samples collected in Brazil (both subsp. pauca and multiplex). Here, we report on a survey of X. fastidiosa genetic diversity (MLST based) performed in six regions in Brazil and two in Argentina, by sampling five different plant species. In addition to the six previously reported ST, seven new subsp. pauca and two new subsp. multiplex ST were identified. The presence of subsp. multiplex in South America is considered to be the consequence of a single introduction from its native range in North America more than 80 years ago. Different phylogenetic approaches clustered the South American ST into four groups, with strains infecting citrus (subsp. pauca); coffee and olive (subsp. pauca); coffee, hibiscus, and plum (subsp. pauca); and plum (subsp. multiplex). In areas where these different genetic clusters occurred sympatrically, we found evidence of homologous recombination in the form of bidirectional allelic exchange between subspp. pauca and multiplex. In fact, the only strain of subsp. pauca isolated from a plum host had an allele that originated from subsp. multiplex. These signatures of bidirectional homologous recombination between endemic and introduced ST indicate that gene flow occurs in short evolutionary time frames in X. fastidiosa, despite the ecological isolation (i.e., host plant species) of genotypes.

Assuntos

RESUMO

Two haplotypes of Xylella fastidiosa subsp. pauca (Xfp) that correlated with their host of origin were identified in a collection of 90 isolates infecting citrus and coffee plants in Brazil, based on a single-nucleotide polymorphism in the gyrB sequence. A new single-nucleotide primer extension (SNuPE) protocol was designed for rapid identification of Xfp according to the host source. The protocol proved to be robust for the prediction of the Xfp host source in blind tests using DNA from cultures of the bacterium, infected plants, and insect vectors allowed to feed on Xfp-infected citrus plants. AMOVA and STRUCTURE analyses of microsatellite data separated most Xfp populations on the basis of their host source, indicating that they were genetically distinct. The combined use of the SNaPshot protocol and three previously developed multilocus SSR markers showed that two haplotypes and distinct isolates of Xfp infect citrus and coffee in Brazil and that multiple, genetically different isolates can be present in a single orchard or infect a single tree. This combined approach will be very useful in studies of the epidemiology of Xfp-induced diseases, host specificity of bacterial genotypes, the occurrence of Xfp host jumping, vector feeding habits, etc., in economically important cultivated plants or weed host reservoirs of Xfp in Brazil and elsewhere.

Assuntos

RESUMO

Aphids are the most important vectors of viruses infecting potato (Solanum tuberosum). We focused on the response of the aphid vector Myzus persicae (Sulzer) to five commercial potatocultivars: Ágata, Jaette Bintje, Mondial, Monalisa and Santè, by traditional antibiosis and antixenosis tests and by the EPG (Electrical Penetration Graph) technique, as a step forward to the design of effective management practices. Our aim was to identify plant factors involved in resistance of these cultivars against M. persicae, both at the surface and in deeper plant tissues. Results from the antixenosis test confirmed a strong preference of M. persicae for the Mondial cultivar. The antibiosis study indicated a lower population development of the aphid in 'Monalisa' when compared to 'Ágata' and 'Jaette Bintje'. EPG assays indicated that 'Santè' inhibited the initial feeding process of M. persicae, whereas 'Monalisa' showed a physical-type of resistance as demonstrated by a very high number of short probes. The cultivar Mondial showed average values for all EPG variables analyzed. The behavior in 'Jaette Bintje' indicated this cultivar was an ideal host for aphid feeding and reproduction. Together, the EPG data revealed the existence of pre and post-phloematics factors in the cultivars under study, which have important implications on the efficiency of transmission and spread of virus in potato by M. persicae.

Assuntos

RESUMO

In some American countries, grapevines are affected by Pierce's disease (PD), which is caused by a particular strain of Xylella fastidiosa not yet reported in Brazil. In order to investigate the potential for PD spread in Brazil in case of pathogen introduction, we conducted a faunistic analysis of leafhoppers (Hemiptera: Cicadellidae) associated to vineyards in the State of Rio Grande do Sul, with emphasis in the subfamily Cicadellinae (sharpshooters), which includes the main potential vectors of X. fastidiosa. Leafhopper samplings were carried out fortnightly during two years (9/2004-9/2006) in four Vitis vinifera vineyards in the municipalities of Bento Gonçalves and Farroupilha (RS). Thirtyfour leafhopper and six spittlebug species were collected, but most (98.4%) of the 3,893 specimens trapped were leafhoppers, distributed in the subfamilies Cicadellinae (60.2%), Gyponinae (34.1%), Deltocephalinae (3.8%) and Coelidinae (0.3%). The sharpshooter specimens were divided in the tribes Cicadellini (68.5%; 12 species) and Proconiini (31.5%; 11 species). Based on the faunistic indices, five species of Cicadellini, Bucephalogonia xanthophis (Berg), Dilobopterus dispar (Germar), Macugonalia cavifrons Stal, Sibovia sagata (Signoret) and Spinagonalia rubrovittata Cavichioli, and three of Proconiini, Molomea consolida (Schöder), Oncometopia facialis (Signoret) and Oncometopia fusca Melichar were prevalent in the vineyards. The high diversity of native sharpshooters in Rio Grande do Sul indicates the existence of a high risk of PD spread if the pathogen is introduced in grapevines.

Assuntos

RESUMO

In some American countries, grapevines are affected by Pierce's disease (PD), which is caused by a particular strain of Xylella fastidiosa not yet reported in Brazil. In order to investigate the potential for PD spread in Brazil in case of pathogen introduction, we conducted a faunistic analysis of leafhoppers (Hemiptera: Cicadellidae) associated to vineyards in the State of Rio Grande do Sul, with emphasis in the subfamily Cicadellinae (sharpshooters), which includes the main potential vectors of X. fastidiosa. Leafhopper samplings were carried out fortnightly during two years (9/2004-9/2006) in four Vitis vinifera vineyards in the municipalities of Bento Gonçalves and Farroupilha (RS). Thirtyfour leafhopper and six spittlebug species were collected, but most (98.4 percent) of the 3,893 specimens trapped were leafhoppers, distributed in the subfamilies Cicadellinae (60.2 percent), Gyponinae (34.1 percent), Deltocephalinae (3.8 percent) and Coelidinae (0.3 percent). The sharpshooter specimens were divided in the tribes Cicadellini (68.5 percent; 12 species) and Proconiini (31.5 percent; 11 species). Based on the faunistic indices, five species of Cicadellini, Bucephalogonia xanthophis (Berg), Dilobopterus dispar (Germar), Macugonalia cavifrons Stal, Sibovia sagata (Signoret) and Spinagonalia rubrovittata Cavichioli, and three of Proconiini, Molomea consolida (Schõder), Oncometopia facialis (Signoret) and Oncometopia fusca Melichar were prevalent in the vineyards. The high diversity of native sharpshooters in Rio Grande do Sul indicates the existence of a high risk of PD spread if the pathogen is introduced in grapevines.

Assuntos

RESUMO

Aphids are the most important vectors of viruses infecting potato (Solanum tuberosum). We focused on the response of the aphid vector Myzus persicae (Sulzer) to five commercial potatocultivars: Ágata, Jaette Bintje, Mondial, Monalisa and Santè, by traditional antibiosis and antixenosis tests and by the EPG (Electrical Penetration Graph) technique, as a step forward to the design of effective management practices. Our aim was to identify plant factors involved in resistance of these cultivars against M. persicae, both at the surface and in deeper plant tissues. Results from the antixenosis test confirmed a strong preference of M. persicae for the Mondial cultivar. The antibiosis study indicated a lower population development of the aphid in 'Monalisa' when compared to 'Ágata' and 'Jaette Bintje'. EPG assays indicated that 'Santè' inhibited the initial feeding process of M. persicae, whereas 'Monalisa' showed a physical-type of resistance as demonstrated by a very high number of short probes. The cultivar Mondial showed average values for all EPG variables analyzed. The behavior in 'Jaette Bintje' indicated this cultivar was an ideal host for aphid feeding and reproduction. Together, the EPG data revealed the existence of pre and post-phloematics factors in the cultivars under study, which have important implications on the efficiency of transmission and spread of virus in potato by M. persicae.

Assuntos

RESUMO

The causal agent of citrus variegated clorosis, Xylella fastidiosa, is transmitted by leafhoppers of the subfamily Cicadellinae, whose species vary regionally. The goal of this study was to identify potential vectors of this pathogen in citrus groves of Bahia North Coast, Brazil. The survey was done from March/2002 to February/2003 in three seven- to nine-year-old sweet orange (Citrus sinensis, Pêra variety) groves located in Rio Real, BA. Fifteen yellow sticky cards (8.5x11.5 cm) were installed 40 m apart in each grove, hanged at 1.5 m high on the upper north side of citrus canopies, and replaced fortnightly. A sweep net was periodically used to sample leafhoppers on herbaceous weeds inside the groves, by selecting five points at random and performing 30 sweeps in each point. A total of 1,360 specimens of 49 Auchenorrhyncha species were collected in this study, mostly in the family Cicadellidae (90.2 percent). The subfamily Cicadellinae, which includes the sharpshooter vectors of X. fastidiosa, showed the largest number of species (14) and specimens (84.8 percent). Acrogonia flagellata Young, A. citrina Marucci & Cavichioli, Homalodisca spottii Takiya, Cavichioli & McKamey and an unidentified Cicadellini (species 1) were the dominant species trapped on citrus canopies, while Hortensia similis (Walker) and Erythrogonia dubia (Medler) were dominant in the weedy vegetation. Among the Cicadellinae species already known as vectors of X. fastidiosa in citrus, only A. citrina, Bucephalogonia xanthophis (Berg) e Ferrariana trivittata (Signoret) were found. The two latter species were accidentally trapped by sweep net in the weedy vegetation.

O agente causal da clorose variegada dos citros, Xylella fastidiosa, é transmitido por cigarrinhas da subfamília Cicadellinae, cujas espécies variam regionalmente. O objetivo deste trabalho foi identificar potenciais vetores do patógeno em pomares cítricos do Litoral Norte da Bahia. Os levantamentos foram conduzidos de mar/2002 a fev/2003, em três propriedades no município de Rio Real, em pomares de laranjeira doce (Citrus sinensis) variedade Pêra, com sete a nove anos. Em cada pomar, 15 cartões adesivos amarelos foram dispostos a 40 m entre si, instalados a 1,5 m de altura em ramos da face norte, na periferia da copa, sendo substituídos quinzenalmente. Também foram realizadas amostragens com rede de varredura na vegetação rasteira dos pomares, em cinco pontos escolhidos aleatoriamente, efetuando-se 30 redadas por ponto. No total, foram coletados 1360 espécimes pertencentes a 49 espécies de Auchenorrhyncha, a maioria da família Cicadellidae (90,2 por cento). A subfamília Cicadellinae, que inclui os vetores de X. fastidiosa, apresentou maior número de espécies (14) e de indivíduos coletados (84,8 por cento). Entre as espécies de Cicadellinae, Acrogonia flagellata Young, A citrina Marucci & Cavichioli, Homalodisca spottii Takiya, Cavichioli & McKamey e uma espécie não-identificada de Cicadellini (espécie 1) foram dominantes na copa das plantas cítricas, enquanto que Hortensia similis (Walker) e Erythrogonia dubia (Medler) foram dominantes na vegetação rasteira. Entre os cicadelíneos já conhecidos como vetores de X. fastidiosa em citros, apenas A. citrina, Bucephalogonia xanthophis (Berg) e Ferrariana trivittata (Signoret) foram observados, sendo que as duas últimas espécies tiveram ocorrência acidental na vegetação rasteira.

Assuntos