There are two bacilliform, rhabdo-like viruses that cause citrus leprosis: Citrus leprosis virus C (CiLV-C), which accumulates in the cytoplasm of infected cells, and Citrus leprosis virus nuclear type (CiLV-N), which accumulates in their nucleus. The first one, the prototype of the new genus Cilevirus, is prevalent and occurs in several countries of the American continent, from Argentina to Mexico (1). The second type, still a tentative member of the Rhabdoviridae family, is of rare occurrence, with a few reports in Brazil and one in Panama (1). Leprosis is particularly important to the Brazilian citrus industry because of the 60 to 80 million dollars spent yearly for the control of Brevipalpus phoenicis (Geijskes, 1939) (Acari: Tenuipalpidae), the vector of the virus (1). For decades, the disease was considered unique to citrus plants; however, greenhouse experiments conducted in the 1990s demonstrated the mechanical transmission of CiLV-C to noncitrus plants (1). Years later, researchers were able to transmit the virus to nonrutaceous hosts using viruliferous mites (1,4). Recently, León et al. (2) reported the occurrence of the first noncitrus plant naturally infected by CiLV-C, the rutaceous Swinglea glutinosa Blanco (Merr.). Tropical spiderworts (Commelina benghalensis L.; Commelinaceae) are monocot weeds commonly found in citrus orchards in Brazil. In a survey conducted in orchards with high incidences of leprosis in the municipalities of Borborema and São José do Rio Preto, State of Sao Paulo, Brazil, tropical spiderworts were found exhibiting necrotic spots with a yellow halo in green leaves and green spots with necrotic center in senescent leaves. Since these symptoms are similar to those caused by CiLV-C in citrus, symptomatic plants were collected and subjected to transmission electron microscopy analyses and reverse transcription-PCR using primers that specifically amplify a region within the putative movement protein gene of the virus (3). Bacilliform virus particles and typical inclusions were seen in the lesions. Bands of the expected 344 bp size were seen in agarose gels of symptomatic samples only. The analysis of the consensus sequence showed 100% identity with CiLV-C sequence available in the GenBank (Accession No. YP_654542.1). Experimental transmission of CiLV-C by B. phoenicis reproduced the lesions in inoculated tropical spiderwort. Also, the virus could be easily transmitted back from C. benghalensis to sweet orange plants. Our data show that this widespread weed is the first monocot as a natural host for CiLV-C. Since tropical spiderwort is a host for B. phoenicis and symptomatic plants were found in two municipalities 130 km apart from each other, it is possible that this weed may serve as reservoir for the virus and play a relevant role in the spread of the disease in the field, but this issue still needs to be addressed in further experiments. References: (1) M. A. Bastianel et al. Plant Dis. 94:284, 2010. (2) M. G. A. Leon et al. Plant Dis. 90:682, 2008. (3) E. C. Locali-Fabris et al. Plant Dis. 87:1317. (4) M. A. Nunes et al. Plant Dis. Online publication. doi:10.1094/PDIS-06-11-0538, 2011.

Plant diseases caused by phytopathogens result in huge economic losses in agriculture. In addition, the use of chemical products to control such diseases causes many problems to the environment and to human health. However, some bacteria and fungi have a mutualistic relationship with plants in nature, mainly exchanging nutrients and protection. Thus, exploring those beneficial microorganisms has been an interesting and promising alternative for mitigating the use of agrochemicals and, consequently, achieving a more sustainable agriculture. Microorganisms are able to produce and excrete several metabolites, but volatile organic compounds (VOCs) have huge biotechnology potential. Microbial VOCs are small molecules from different chemical classes, such as alkenes, alcohols, ketones, organic acids, terpenes, benzenoids and pyrazines. Interestingly, volatilomes are species-specific and also change according to microbial growth conditions. The interaction of VOCs with other organisms, such as plants, insects, and other bacteria and fungi, can cause a wide range of effects. In this review, we show that a large variety of plant pathogens are inhibited by microbial VOCs with a focus on the in vitro and in vivo inhibition of phytopathogens of greater scientific and economic importance in agriculture, such as Ralstonia solanacearum, Botrytis cinerea, Xanthomonas and Fusarium species. In this scenario, some genera of VOC-producing microorganisms stand out as antagonists, including Bacillus, Pseudomonas, Serratia and Streptomyces. We also highlight the known molecular and physiological mechanisms by which VOCs inhibit the growth of phytopathogens. Microbial VOCs can provoke many changes in these microorganisms, such as vacuolization, fungal hyphal rupture, loss of intracellular components, regulation of metabolism and pathogenicity genes, plus the expression of proteins important in the host response. Furthermore, we demonstrate that there are aspects to investigate by discussing questions that are still not very clear in this research area, especially those that are essential for the future use of such beneficial microorganisms as biocontrol products in field crops. Therefore, we bring to light the great biotechnological potential of VOCs to help make agriculture more sustainable.

The emergence of citrus huanglongbing (HLB) has been a constraint for worldwide citrus growers. HLB disease is associated to species of the biothrophic bacteria Candidatus Liberibacter spp. (CaL). In this study, we assessed the transcriptional status of salicylic acid (SA) genes and associated defenses between two contrasting citrus genotypes during challenge with Ca. Liberibacter asiaticus or Ca. Liberibacter americanus. Citrus sinensis exhibited the most evident alterations in gene expression of evaluated genes, when compared with Poncirus trifoliata. Upstream pathway SA genes showed a slight upward regulation in C. sinensis. Salicylic acid biosynthesis and accumulation might be impaired as we observed a low expression level of SA biosynthesis related genes. Moreover, genes associated to SA metabolism showed a slight induction. These results may account for the absence of significant downstream defense response related to salicylic acid. Leaf anatomical analysis revealed callose accumulation in both HLB infected, C. sinensis and P. trifoliata sieve tube elements (STE), although only C. sinensis exhibited collapsed STE. Our data corroborate other studies and suggest that the SA biosynthesis and metabolism related genes might be involved in the contrasting response to CaL in different citrus genotypes. Additionally, we suggest that collapsed STE might have a prominent implication in symptomatology of highly susceptible plants. Index terms: SAR, plant-pathogen interaction, gene expression, callose deposition. Análises genéticas das respostas de defesas mediadas por ácido salicílicoe histopatologia no patossistema huanglongbing RESUMO A ocorrência do huanglongbing (HLB) dos citros tem sido um sério problema para os citricultores em todo o mundo. O HLB está associado a bactérias biotróficas da espécie Candidatus Liberibacter spp. (CaL). Nesse estudo, nós avaliamos o perfil transcricional dos genes da via do ácido salicílico (SA) e genes associados a defesa em dois genótipos contrastantes após desafio com Ca. Liberibacter asiaticus ou Ca. Liberibacter americanus. Citrus sinensis exibiu maiores alterações na expressão gênica dos genes avaliados, quando comparado com Poncirus trifoliata. Genes upstream da via do Oliveira et al.

No abstract