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Citrus leprosis (CL) is the main viral disease affecting the Brazilian citriculture. Sweet orange (Citrus sinensis L. Osbeck) trees affected by CL were identified in small orchards in Southern Brazil. Rod-like particles of 40 × 100 nm and electron lucent viroplasm were observed in the nucleus of infected cells in symptomatic tissues. RNA extracts from three plants, which proved negative by RT-PCR for known CL-causing viruses, were analyzed by high throughput sequencing and Sanger sequencing after RT-PCR. The genomes of bi-segmented ss(-)RNA viruses, with ORFs in a typical organization of members of the genus Dichorhavirus, were recovered. These genomes shared 98-99% nt sequence identity among them but <73% with those of known dichorhavirids, a value below the threshold for new species demarcation within that genus. Phylogenetically, the three haplotypes of the new virus called citrus bright spot virus (CiBSV) are clustered with citrus leprosis virus N, which is a dichorhavirus transmitted by Brevipalpus phoenicis sensu stricto. In CiBSV-infected citrus plants, B. papayensis and B. azores were found, but the virus could only be transmitted to Arabidopsis plants by B. azores. The study provides the first evidence of the role of B. azores as a viral vector and supports the assignment of CiBSV to the tentative new species Dichorhavirus australis.

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Aphids are worldwide pests, and in South America, they harm many crops including winter cereals. In the 1970s, the rapid expansion of the wheat crop area in the subtropical region of South America led to growth of aphid populations. The wide availability of food, associated with the low effectiveness of natural biological control, put the aphid populations out of balance, requiring intensive use of insecticides. At the end of the decade, biological control programs of aphids were initiated in Argentina, Brazil, and Chile, including the importation of natural enemies (mainly parasitoids), followed by their laboratory rearing and field release. With decreased use of highly hazardous pesticides, biological control by introduced and already-present parasitoid species was enhanced. The program was very successful and aphid populations have been kept at low levels. This review article explores the history of this program and its current status. In modern day agriculture, with intense multiple cropping systems, adoption of several conservation practices, and increased cultivation of wheat in tropical regions, we discuss ways to keep this program effective to maintain aphid populations on cereal crops at low acceptable levels through employing biological control agents.

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Since 1948, pale yellow wheat spike have been reported in southern Brazil. This symptom was associated with tenuiviruses due to the observation of cytoplasmic inclusions constituted by a mass of filamentous particles (7-10 nm in diameter) with indeterminate length, identical to those found in "leaf dip" preparations. Such symptoms are still seen in wheat crops; however, there is a lack of information regarding this pathosystem. Decades after the first report, the first sequences of wheat white spike virus were characterized. Wheat plants with symptoms such as pale yellowing, chlorotic streaks, and leaf mosaic were collected in Paraná State, Southern Brazil. High-throughput sequencing was used to determine the nearly complete nucleotide sequence of the viral genome. The genome is composed of five RNAs with a total size of 18,129 nucleotides, with eight open reading frames (ORFs). The virus identified in this study can be included in a new species in the family Phenuiviridae, genus Tenuivirus, and we have tentatively named this virus "wheat white spike virus".

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In different parts of the world, aphid populations and their natural enemies are influenced by landscapes and climate. In the Neotropical region, few long-term studies have been conducted, maintaining a gap for comprehension of the effect of meteorological variables on aphid population patterns and their parasitoids in field conditions. This study describes the general patterns of oscillation in cereal winged aphids and their parasitoids, selecting meteorological variables and evaluating their effects on these insects. Aphids exhibit two annual peaks, one in summer-fall transition and the other in winter-spring transition. For parasitoids, the highest annual peak takes place during winter and a second peak occurs in winter-spring transition. Temperature was the principal meteorological regulator of population fluctuation in winged aphids and parasitoids during the year. The favorable temperature range is not the same for aphids and parasitoids. For aphids, temperature increase resulted in population growth, with maximum positive effect at 25°C. Temperature also positively influenced parasitoid populations, but the growth was asymptotic around 20°C. Although rainfall showed no regulatory function on aphid seasonality, it influenced the final number of insects over the year. The response of aphids and parasitoids to temperature has implications for trophic compatibility and regulation of their populations. Such functions should be taken into account in predictive models.

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Wheat blast, caused by Pyricularia oryzae Triticum lineage, is a major constraint to wheat production, mainly in the tropics of Brazil, where severe epidemics have been more frequent. We analyzed disease and wheat yield data from 42 uniform field trials conducted over 9 years (2012 to 2020) to assess whether the percent control and yield response were influenced by fungicide type, region (tropical or subtropical), and year. Six treatments were selected, all evaluated in at least 19 trials. Two fungicides were applied as solo active ingredients (MANCozeb, and TEBUconazole), and four were premixes (AZOXystrobin plus TEBU, TriFLoXystrobin plus PROThioconazole, TFLX plus TEBU, and PYRAclostrobin plus EPOXiconazole). Percent control, calculated from back-transforming estimates by a meta-analysis network model fitted to the log of the means, ranged from 43 to 58%, with all but PYRA plus EPOX showing efficacy >52% on average, not differing among them. The variation in both efficacy and yield response was explained by region, and all but TEBU performed better in the subtropics than in the tropics. Yield response from using three sequential sprays was approximately two times greater in the subtropics (319 to 532 kg/ha) than in the tropics (149 to 241.3 kg/ha). No significant decline in fungicide efficacy or yield response was observed in 9 years of study for any of the fungicides. These results reinforce the need to improve control by adopting an integrated management approach in the tropics given poorer performance and lower profitability, especially for the premixes, than in the subtropics.

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Rice (Oryza sativa L.) is an important food crop for humanity, being cultivated in tropical and temperate regions of the world. This study reports the nearly complete genome sequences of four Brazilian rice stripe necrosis virus (RSNV) isolates. The nucleotide sequences of the RNA1 and RNA2 genome segments of these Brazilian isolates were 96.5 to 99.9% identical, indicating their close phylogenetic relationship to each other. Phylogeny and recombination analysis indicated that the genome of one of the isolates consisted of RNA segments of different origins, suggesting that a reassortment event had occurred.

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Fusarium head blight (FHB), caused mainly by Fusarium graminearum, is best controlled with demethylation inhibitor (DMI) fungicides during flowering. However, the use of premixes of DMI and quinone outside inhibitor (QoI) fungicides to control FHB has increased in Brazil. Data on FHB severity and wheat yields measured in field experiments conducted in Brazil were gathered from both peer- and nonpeer-reviewed sources published from 2000 to 2018. After selection criteria were applied, 73 field trials from 35 bibliographic sources were identified, among which 50% of the data were obtained from cooperative network trials conducted after 2011. To be included in the analysis, DMI plus QoI premixes or tebuconazole were tested in at least 14 trials and 3 years. Four premixes met the criteria. Estimates of percent control (and respective 95% confidence intervals) by a network model fitted to the log of the treatment means ranged from 44.1% (pyraclostrobin plus metconazole applied once; 32.4 to 53.7) to 64.3% (pyraclostrobin plus metconazole; 58.4 to 69.3); the latter did not differ from tebuconazole (59.9%; 53.6 to 65.3). Yield response was statistically similar for pyraclostrobin plus metconazole (532.1 kg/ha; 441 to 623) and trifloxystrobin plus prothioconazole (494.9 kg/ha; 385 to 551), and both differed statistically from a group composed of tebuconazole (448.2 kg/ha; 342 to 554), trifloxystrobin plus tebuconazole (468.2 kg/ha; 385 to 551), azoxystrobin plus tebuconazole (462.4 kg/ha; 366 to 558), and pyraclostrobin plus metconazole applied once (413.7 kg/ha; 308 to 518). The two categories of FHB index (7% cutoff) and yield (3,000 kg/ha cutoff), both in the nontreated check, did not explain the heterogeneity in the estimates. Considering only the fungicide effects on yield, two sequential sprays of tebuconazole or one spray of pyraclostrobin plus metconazole as management choices are likely more profitable than DMI plus QoI premixes sprayed twice during flowering.

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O tratamento de sementes (TS) é uma importante ferramenta no manejo de doenças na cultura do trigo, embora poucos produtos sejam indicados para esse fim. Por isso, a pesquisa deve realizar trabalhos relacionados à efetividade de diferentes produtos no TS e também o possível efeito fitotóxico. Os objetivos deste trabalho foram realizar testes fisiológicos em sementes e avaliar o desenvolvimento de duas cultivares de trigo (BRS Guamirim e TBIO Toruk), submetidas a 13 diferentes tratamentos de sementes. Para cada tratamento foram analisados a germinação e o vigor. As sementes tratadas também foram semeadas a campo, onde se determinou a emergência a campo e massa fresca de raiz e parte aérea. As sementes tratadas com azoxistrobina e Bacillus amyloliquefaciens resultaram em decréscimo na germinação da cultivar TBIO Toruk. Na análise do vigor houve diferença entre os tratamentos testados para as duas cultivares, sendo que houve redução do vigor em sementes tratadas com dimetomorfe para TBIO Toruk e azoxistrobina para a cultivar BRS Guamirim. As sementes submetidas ao tratamento Carboxamida A resultaram em plântulas com maiores valores de massa fresca de raiz e parte aérea. Os resultados apresentados permitem a seleção de produtos com baixa ou ausência de fitotoxidade para incorporação no manejo de doenças no trigo.

Seed treatment (ST) is an important tool in the management of diseases in the wheat crop, although few products are indicated for this purpose. The research must carry out studies related to the ST effectiveness using different products and the possible phytotoxic effect. The aim of this study was to perform physiological tests on seeds and evaluate the development of two wheat cultivars (BRS Guamirim and TBIO Toruk), submitted to 13 different ST. Germination and vigor were analyzed for each treatment. The treated seeds were also sown to the field, where the field emergence and fresh root and shoot mass were determined. In the germination test, the seeds treated azoxystrobin and Bacillus amyloliquefaciens presented a decrease in the cultivar TBIO Toruk. Vigor analyzes indicated differences between treatments in the two cultivars, and the dimethomorph treatment presented the lowest vigor for TBIO Toruk and azoxystrobin for the BRS Guamirim. The seeds submitted to the Carboxamide A treatment showed seedlings the highest values of fresh root and shoot mass. The results presented allow the selection of products with low or no phytotoxicity for incorporating in wheat disease management.

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RESUMO

O tratamento de sementes (TS) é uma importante ferramenta no manejo de doenças na cultura do trigo, embora poucos produtos sejam indicados para esse fim. Por isso, a pesquisa deve realizar trabalhos relacionados à efetividade de diferentes produtos no TS e também o possível efeito fitotóxico. Os objetivos deste trabalho foram realizar testes fisiológicos em sementes e avaliar o desenvolvimento de duas cultivares de trigo (BRS Guamirim e TBIO Toruk), submetidas a 13 diferentes tratamentos de sementes. Para cada tratamento foram analisados a germinação e o vigor. As sementes tratadas também foram semeadas a campo, onde se determinou a emergência a campo e massa fresca de raiz e parte aérea. As sementes tratadas com azoxistrobina e Bacillus amyloliquefaciens resultaram em decréscimo na germinação da cultivar TBIO Toruk. Na análise do vigor houve diferença entre os tratamentos testados para as duas cultivares, sendo que houve redução do vigor em sementes tratadas com dimetomorfe para TBIO Toruk e azoxistrobina para a cultivar BRS Guamirim. As sementes submetidas ao tratamento Carboxamida A resultaram em plântulas com maiores valores de massa fresca de raiz e parte aérea. Os resultados apresentados permitem a seleção de produtos com baixa ou ausência de fitotoxidade para incorporação no manejo de doenças no trigo.(AU)

Seed treatment (ST) is an important tool in the management of diseases in the wheat crop, although few products are indicated for this purpose. The research must carry out studies related to the ST effectiveness using different products and the possible phytotoxic effect. The aim of this study was to perform physiological tests on seeds and evaluate the development of two wheat cultivars (BRS Guamirim and TBIO Toruk), submitted to 13 different ST. Germination and vigor were analyzed for each treatment. The treated seeds were also sown to the field, where the field emergence and fresh root and shoot mass were determined. In the germination test, the seeds treated azoxystrobin and Bacillus amyloliquefaciens presented a decrease in the cultivar TBIO Toruk. Vigor analyzes indicated differences between treatments in the two cultivars, and the dimethomorph treatment presented the lowest vigor for TBIO Toruk and azoxystrobin for the BRS Guamirim. The seeds submitted to the Carboxamide A treatment showed seedlings the highest values of fresh root and shoot mass. The results presented allow the selection of products with low or no phytotoxicity for incorporating in wheat disease management.(AU)

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The majority of Old World monopartite begomoviruses (family Geminiviridae) are associated with satellite DNAs. Alphasatellites are capable of autonomous replication, but depend on the helper virus for movement, encapsidation and transmission by the insect vector. Recently, Euphorbia yellow mosaic alphasatellite (EuYMA) was found in association with Euphorbia yellow mosaic virus (EuYMV) infecting Euphorbia heterophylla plants in Brazil. The geographical range of EuYMA was assessed in a representative sampling of E. heterophylla plants collected in several states of Brazil from 2009 to 2014. Infectious clones were generated and used to assess the phenotype of viral infection in the presence or absence of the alphasatellite in tomato, E. heterophylla, Nicotiana benthamiana, Arabidopsis thaliana and Crotalaria juncea. Phenotypic differences of EuYMV infection in the presence or absence of EuYMA were observed in A. thaliana, N. benthamiana and E. heterophylla. Symptoms were more severe when EuYMV was inoculated in combination with EuYMA in N. benthamiana and E. heterophylla, and the presence of the alphasatellite was determinant for symptom development in A. thaliana. Quantification of EuYMV and EuYMA indicated that EuYMA affects the accumulation of EuYMV during infection on a host-dependent basis. Transmission assays indicated that EuYMA negatively affects the transmission of EuYMV by Bemisia tabaci MEAM1. Together, these results indicate that EuYMA is capable of modulating symptoms, viral accumulation and whitefly transmission of EuYMV, potentially interfering with virus dissemination in the field.

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