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Papaya ringspot virus-type W (PRSV-W) is the most prevalent and important viral pathogen of cucurbits in Brazil. It can be effectively controlled by the incorporation of genetic resistance into susceptible melon cultivars. The present study identified amplified fragment length polymorphic (AFLP) markers linked to the PRSV-W resistance Prv1 allele. The susceptible yellow-fleshed melon-breeding line AF426 prv1 and its nearly isogenic-resistant line AF426 Prv1, which carries the Prv1 allele resident in the Indian cantaloupe U.S. Plant Introduction (PI) 180280, were screened for AFLP marker polymorphisms. Of 30 251 AFLP loci, only three were polymorphic between the nearly isogenic lines. Segregation analyses for these three polymorphic markers and the Prv1 allele using a BC1 population of 197 plants indicated close linkage (0.5% recombination frequency) between marker EK190 ( HindIII-CGA and MseI-GTG; 190 bp) and Prv1. Thus, EK190 might be a useful marker in breeding programmes aiming to develop melon cultivars resistant to PRSV-W. The other two markers are closely linked to each other, but distantly linked to Prv1. [ABSTRACT FROM AUTHOR]

Two surveys (2005/2006 and 2009) were conducted in the state of São Paulo, Brazil, to investigate the incidence of ' Candidatus Liberibacter asiaticus' and ' Ca. L. americanus', two liberibacters associated with citrus huanglongbing (HLB) disease and both transmitted by Diaphorina citri, in orange jasmine ( Murraya exotica), a widespread ornamental tree in cities and villages. The graft-transmissibility of the two species, and their DNA relatedness to citrus-associated liberibacters, were also investigated. Quantitative PCR was applied to PCR-positive orange jasmine and HLB-positive citrus growing in backyards and orchards to assess their inoculum source potentials. Liberibacters were detected in 91 of 786 sampled orange jasmine plants in 10 of 76 sampled locations. PCR-positive trees exhibited yellow shoots and/or dieback symptoms indistinguishable from those on PCR-negative trees. ' Candidatus Liberibacter americanus' was more common in 2005/2006 (96·6%) and ' Ca. L. asiaticus' in 2009 (84·8%). rplJ nucleotide sequences were identical within all populations of either species. Graft transmission succeeded only in homologous host combinations, including ' Ca. L. americanus' (2/10) from/to orange jasmine and ' Ca. L. americanus' (5/18) and ' Ca. L. asiaticus' (5/9) from/to citrus. Symptoms were mild and developed less rapidly in orange jasmine than in citrus, probably as a result of lower liberibacter multiplication rates. Respective titres of ' Ca. L. americanus' and ' Ca. L. asiaticus' in orange jasmine averaged 4·3 and 3·0 log cells g tissue, compared with 5·5 and 7·3 in citrus. The results indicate that orange jasmine does not favour liberibacter multiplication as much as citrus. However, its importance in HLB epidemics should not be underestimated as it is a preferred host of D. citri and is not under any strict tree-eradication programme or measures for insect control. [ABSTRACT FROM AUTHOR]

Phytoplasmas are associated with several plant diseases occurring in Brazil. A phytoplasma of group 16SrIII found in tomato plants with symptoms of big bud was identified by polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) of 16S rDNA. RFLP patterns using HhaI and RsaI endonucleases were distinct from those exhibited by phytoplasmas representatives of diverse subgroups of group 16SrIII. Nucleotide sequence analyses demonstrated sequence heterogeneity expressed through a few base positions and restriction site among cloned fragments, revealing lineages different from members of currently known subgroups. The detection of lineages within tomato big bud phytoplasma present in Brazil revealed the diversity of representatives of group 16SrIII in tropical ecosystem and confirmed the genetic diversity of phytoplasmas of that group around the world. [ABSTRACT FROM AUTHOR]

Discusses a comparative analysis of seven genome sequences from plant-associated bacteria. Structural comparisons between the genomes; Mechanisms of DNA exchange; Genome sequencing of plant-associated bacteria; Gene category distribution of the genomes of plant-associated bacteria.

Ratoon stunting disease ( RSD), caused by the bacterium Leifsonia xyli subsp. xyli (Lxx), is one of the most economically important diseases of sugarcane worldwide. Because knowledge on the interaction of Lxx with its host at the microscopic level is limited, the development of tools to monitor Lxx during the colonization process could shed new light on the processes that control disease development. In this investigation, a transformation protocol was optimized and a mutant Lxx strain engineered that stably expressed the gfp gene in sugarcane tissues. In vitro, the growth of the mutant did not differ from that of the wild type. Also, plants inoculated with both strains showed comparable growth and development when analysed 180 days after inoculation (dai). Fluorescence microscopy of roots, stalks, meristems and leaf tissues of Lxx- GFP-inoculated plants was performed at 180 dai. In the leaves, Lxx-tagged cells were observed within the xylem vessels as has been described before but, in addition, they were found in a new niche within the host tissues, in the mesophyll and in the bundle sheath cells surrounding the vascular system. This finding indicates that Lxx is able to move from the xylem to the parenchyma of the leaf cells. This first report of an Lxx mutant expressing a heterologous gene revealed that colonization of sugarcane by this pathogen is not limited to the xylem vessels as commonly reported. [ABSTRACT FROM AUTHOR]

The application of silicon to the roots or leaves reduces the severity of powdery mildew ( Podosphaera xanthii) in melon but the latter treatment is less effective. This study compared key biochemical defence responses of melon triggered by P. xanthii after root or foliar treatment with potassium silicate ( PS). Treatments consisted of pathogen-inoculated or mock-inoculated plants supplied with PS via roots or foliarly, as well as a non-treated control. The activity of defence enzymes and the concentration of phenolic compounds, lignin and malondialdehyde were determined from leaf samples at different time points after inoculation. Pathogen-inoculated plants irrigated with PS showed both an accumulation of silicon and primed defence responses in leaves that were not observed in pathogen-inoculated plants either sprayed with PS or not treated. These responses included the anticipated activity of peroxidase and accumulation of soluble phenols, the activation of chitinase and repression of catalase, and the stronger activation of superoxide dismutase, peroxidase and β-1,3-glucanase. Moreover, the lignin concentration increased in response to inoculation, whereas the malondialdehyde concentration decreased. For the foliar treatment, however, only an increase in lignin deposition was observed compared with the control plants. The results show that silicon strongly plays an active role in modulating the defence responses of melon against P. xanthii when supplied to the roots as opposed to the foliage. [ABSTRACT FROM AUTHOR]

The effects of silicon (Si) supplied in the form of potassium silicate (PS) were evaluated on epidemic components of powdery mildew of melon under greenhouse conditions. The PS was applied to the roots or to leaves. In the first experiment, epidemic components were evaluated after inoculation with Podosphaera xanthii. In the second experiment, the disease progress rate was evaluated on plants subjected to natural infection. The area under the disease progress curve was reduced by 65% and 73% in the foliar and root treatments, respectively, compared to control plants, as a consequence of reductions in infection efficiency, colony expansion rate, colony area, conidial production and disease progress rate. However, root application of PS was more effective than foliar application in reducing most of the epidemic components, except for infection efficiency. This can be explained by the high Si concentration in leaf tissues with root application, in contrast to the foliar treatment where Si was only deposited on the external leaf surfaces. The effects of PS reported in this study demonstrated that powdery mildew of melon can be controlled, and that the best results can be achieved when PS is supplied to the roots. [ABSTRACT FROM AUTHOR]

The broadest based resistance to anthracnose of common bean (Phaseolus vulgaris L.) is conferred by the Co-4 locus. We sequenced a bacterial artificial chromosome clone harboring part of the Co-4 locus of the bean genotype Sprite and assembled a single contig of 106.5 kb for functional annotation. This region contained five copies of the COK-4 gene that encodes for a serine threonine kinase protein previously mapped to the Co-4 locus and 19 novel genes with no similarity to any previously identified genes of common bean. Several putative genes of the Co-4 locus seemed to be expressed as they matched perfectly with bean expressed sequence tags. The expression of the COK-4 genes was assessed by reverse transcription (RT)-PCR, and a single 850-bp cDNA fragment was sequenced and compared with the genomic sequences of the COK-4 homologs. Although the COK-4 cDNA was isolated from a different bean cultivar, it showed high similarity (95%) to the exons of genes BA17 and BA21, suggesting that they were expressed. In a phylogenetic tree including all currently available Pto-like sequences from Phaseolus species, the COK-4 homologs formed a single cluster with the Pto gene, whereas two sequences from P. coccineus and all sequences of P. vulgaris formed two closely related clusters. The Co-4 locus was physically mapped to the short arm of bean chromosome 3, which corresponds to linkage group B8. This study represents a first step in gaining an understanding of the genomic organization of an anthracnose resistance locus of common bean and provides molecular data for comparative analysis with other plant species. [ABSTRACT FROM AUTHOR]

In Brazil plants of Pfaffia glomerata with mosaic symptoms were found to be infected with a previously undescribed potyvirus, Pfaffia mosaic virus (PfMV). Virus particles were long and flexuous, c. 10 × 700–800 nm, and cylindrical inclusions typical of potyviruses were present in cells of infected tissue. Partial host-range studies revealed that in addition to P. glomerata, PfMV infected only Chenopodium amaranticolor and Chenopodium quinoa. It was efficiently transmitted by the aphids Aphis gossypii and Myzus persicae. Polyclonal antiserum produced against the PfMV coat protein (CP) reacted with Potato virus Y (PVY), but not with four other potyviruses in PTA-ELISA. The similarity of the nucleotide sequence of the PfMV coat-protein gene (CP) varied from 7 to 76% when compared with other members of the family Potyviridae. Similarity of the 3′ NTR sequence varied from 4 to 23%. In both cases the highest similarity was with PVY. These data indicate that PfMV is a new species in the genus Potyvirus. [ABSTRACT FROM AUTHOR]

During the spring of 2001, approximately 10 000 yellow passion flower plants, from two orchards in the county of Livramento de Nossa Senhora, Bahia State, Brazil, exhibited intense yellow mosaic symptoms and drastic reduction of the leaf lamina and plant development. A large population of whiteflies ( Bemisia tabaci) was also found colonizing the plants. All field samples collected tested positive for Passion fruit woodiness virus in DAS-ELISA. Five out of 20 passion flower plants inoculated with adult whiteflies collected from diseased plants in the field developed symptoms 20–30 days after inoculation. Two of these plants gave a positive reaction in TAS-ELISA using antiserum against a begomovirus. Degenerated PCR primers amplified viral DNA fragments from the DNA-A and DNA-B components of a begomovirus infecting these plants. The fragment corresponding to the core region of the coat protein (DNA-A) was cloned and sequenced. A phylogenetic analysis placed this begomovirus isolated from passion flower in the same clade of the New World begomoviruses as several other species from Brazil. Based on the symptoms induced by this virus alone, the disease was tentatively named passion flower little leaf mosaic. [ABSTRACT FROM AUTHOR]

Passiflora alata is one of the commercialized species of the passion vines, grown for its edible fruits. It is found in South America, mainly Paraguay, Argentina, Peru and Brazil. The development of a set of microsatellite markers was proposed to provide tools for analysing both genetic structure of wild populations and the reproductive system of the species, which are poorly understood. Seven markers were developed from a P. alata-genomic library enriched for simple sequence repeats (SSR). Twelve individuals were genotyped, and the levels of the expected heterozygosity ( HE) did show that those markers could be used to develop P. alata genetic studies. [ABSTRACT FROM AUTHOR]

Here we described the development of the first set of Passiflora microsatellite loci isolated from an enriched genomic library. A sample of 43 individuals from 12 accessions of the yellow passion fruit was used to characterize those loci, which revealed up to 20 alleles per locus. Two loci were monomorphic. The observed (HO) and expected (HE) heterozygosities were very similar, as expected for a self-incompatible species. A llelic diversity (HT) was 0.444. This set of markers will permit genetic structure analyses of cultivated and wild populations of Passiflora, and contribute for integrating genetic maps based on dominant markers, as they can provide bridge alleles. [ABSTRACT FROM AUTHOR]

An abstract of the article "First Report of Powdery Mildew on Flamboyant Tree Caused by Erysiphe quercicola in Brazil," by L. J. Dallagnol and colleagues is presented.