The wheat curl mite (WCM), Aceria tosichella, and the plant viruses it transmits represent an invasive mite-virus complex that has affected cereal crops worldwide. The main damage caused by WCM comes from its ability to transmit and spread multiple damaging viruses to cereal crops, with Wheat streak mosaic virus (WSMV) and Wheat mosaic virus (WMoV) being the most important. Although WCM and transmitted viruses have been of concern to cereal growers and researchers for at least six decades, they continue to represent a challenge. In older affected areas, for example in North America, this mite-virus complex still has significant economic impact. In Australia and South America, where this problem has only emerged in the last decade, it represents a new threat to winter cereal production. The difficulties encountered in making progress towards managing WCM and its transmitted viruses stem from the complexity of the pathosystem. The most effective methods for minimizing losses from WCM transmitted viruses in cereal crops have previously focused on cultural and plant resistance methods. This paper brings together information on biological and ecological aspects of WCM, including its taxonomic status, occurrence, host plant range, damage symptoms and economic impact. Information about the main viruses transmitted by WCM is also included and the epidemiological relationships involved in this vectored complex of viruses are also addressed. Management strategies that have been directed at this mite-virus complex are presented, including plant resistance, its history, difficulties and advances. Current research perspectives to address this invasive mite-virus complex and minimize cereal crop losses worldwide are also discussed.

Triazole and benzimidazole fungicides have been used for controlling Fusarium head blight (FHB) in wheat for over two decades. In Brazil, it was only during the last five years that uniform fungicide trials for FHB control have been established yearly, thus contributing to a new large body of fungicide efficacy data for this country. A systematic review of both peer- and non-peer-reviewed studies on chemical control conducted since 2000 in Brazil was performed. Fungicides of interest were the triazoles tebuconazole (TEBU_1x and TEBU_2x) and propiconazole (PROP_2x), and the benzimidazole carbendazim (CARB_2x). Most fungicides were applied twice, the first at early to mid-flowering and the second 7 to 10 days later. Only TEBU was tested as one or two applications, and thus four treatments were evaluated. For these fungicides, there were 35 trials reporting FHB index and 48 reporting mean yield. Network meta-analytic models were fitted to the data of the log of the means of FHB index for each fungicide and for the nontreated check. The meta-analytic estimates were used to obtain control efficacy ([ ]), or percent disease reduction relative to the nontreated check. The absolute mean difference ([ ]) in yield (kg/ha) between the fungicide-treated and the nontreated check plots was also estimated. Yield response relative to the nontreated check ([ ]) was also calculated based on the difference in the logs of the means of yield between fungicide-treated and nontreated check. The TEBU_1x, TEBU_2x, and CARB_2x treatments performed similarly with regards to control efficacy (= 59%, 53% and 55%, respectively), and although better than PROP_2x (47%), the difference was marginally significant. Yield response ([ ]) was highest for TEBU_2x, ([ ] = 558 kg/ha, [ ] = 19.2%) followed by PROP_2x (497 kg/ha, 16.0%), TEBU_1x (457 kg/ha, 17.3%), and CARB_2x (456 kg/ha, 12.8%). For an average 2016 scenario of fungicide plus application costs (F_C = $18 U.S./ha) and average wheat price (W_P = $215 U.S./MT), the probability of breaking even on the financial investment in the four treatments ranged from 59 to 63%. For 140 scenarios (four fungicides) created based on the combination of five W_P ($133 to 266 U.S./MT) and seven F_C ($5 to 35 U.S./ha), the probability of breaking even was >50% for all but two scenarios. The information may serve as a guide for planning future trials and provides a baseline and first step toward optimizing FHB management in Brazil.

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.

Begomoviruses (whitefly‐transmitted, single‐stranded DNA plant viruses) are among the most damaging pathogens causing epidemics in economically important crops worldwide. Besides cultivated plants, many weed and wild hosts act as virus reservoirs where recombination may occur, resulting in new species. The aim of this study was to further characterise the diversity of begomoviruses infecting two major weed genera, Sida and Leonurus. Total DNA was extracted from samples collected in the states of Rio Grande do Sul, Paraná and Mato Grosso do Sul during the years 2009–2011. Viral genomes were enriched by rolling circle amplification (RCA), linearised into unit length genomes using various restriction enzymes, cloned and sequenced. A total of 78 clones were obtained: 37 clones from Sida spp. plants and 41 clones from Leonurus sibiricus plants. Sequence analysis indicated the presence of six bipartite begomovirus species and two alphasatellites. In Sida spp. plants we found Sida micrantha mosaic virus (SiMMV), Euphorbia yellow mosaic virus (EuYMV), and three isolates that represent new species, for which the following names are proposed: Sida chlorotic mottle virus (SiCMoV), Sida bright yellow mosaic virus (SiBYMV) and Sida golden yellow spot virus (SiGYSV), an Old World‐like begomovirus. L. sibiricus plants had a lower diversity of begomoviruses compared to Sida spp., with only Tomato yellow spot virus (ToYSV) and EuYMV (for the first time detected infecting plants of the genus Leonurus) detected. Two satellite DNA molecules were found: Euphorbia yellow mosaic alphasatellite, for the first time detected infecting plants of the genus Sida, and a new alphasatellite associated with ToYSV in L. sibiricus. These results constitute further evidence of the high species diversity of begomoviruses in non‐cultivated hosts, particularly Sida spp.

Eucalypts are susceptible to a wide range of diseases. One of the most important diseases that affect Eucalyptus plantations worldwide is caused by the rust fungus Puccinia psidii. Here, we provide evidence on the complex genetic control of rust resistance in Eucalyptus inter-specific hybrids, by analyzing a number of full-sib families that display different patterns of segregation for rust resistance. These families are totally unrelated to those previously used in other inheritance studies of rust resistance. By using a full genome scan with 114 genetic markers (microsatellites and expressed sequence tag derived microsatellites) we also corroborated the existence and segregation of a resistance locus, explaining 11.5% of the phenotypic variation, on linkage group 3, corresponding to Ppr1. This find represents an additional validation of this locus in totally unrelated pedigree. We have also detected significant additive × additive digenic interactions with LOD >10.0 on several linkage groups. The additive and epistatic QTLs identified explain between 29.8 and 44.8% of the phenotypic variability for rust resistance. The recognition that both additive and non-additive genetic variation (epistasis) are important contributors to rust resistance in eucalypts reveals the complexity of this host-pathogen interaction and helps explain the success that breeding has achieved by selecting rust-resistant clones, where all the additive and non-additive effects are readily captured. The positioning of epistatic QTLs also provides starting points to look for the underlying genes or genomic regions controlling this phenotype on the upcoming E. grandis genome sequence.