BackgroundPlanthoppers not only severely affect crops by causing mechanical damage when feeding but are also vectors of several plant virus species. The analysis of gene expression in persistently infected planthoppers might unveil the molecular basis of viral transmission. Quantitative real-time RT-PCR (RT-qPCR) is currently the most accurate and sensitive method used for quantitative gene expression analysis. In order to normalize the resulting quantitative data, reference genes with constant expression during the experimental procedures are needed.ResultsPartial sequences of the commonly used reference genes actin (ACT), α1-tubulin (TUB), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), elongation factor 1 alpha (EF1A), ribosomal protein S18 (RPS18) and polyubiquitin C (UBI) from Delphacodes kuscheli, a planthopper capable of persistently transmitting the plant fijivirus Mal de Río Cuarto virus (MRCV), were isolated for the first time. Specific RT-qPCR primers were designed and the expression stability of these genes was assayed in MRCV-infective and naïve planthoppers using geNorm, Normfinder and BestKeeper tools. The overall analysis showed that UBI, followed by 18S and ACT, are the most suitable genes as internal controls for quantitative gene expression studies in MRCV-infective planthoppers, while TUB and EF1A are the most variable ones. Moreover, EF1A was upregulated by MRCV infection.ConclusionsA RT-qPCR platform for gene expression analysis in the MRCV-infected planthopper vector Delphacodes kuscheli was developed. Our work is the first report on reference gene selection in virus-infected insects, and might serve as a precedent for future gene expression studies on MRCV and other virus-planthopper pathosystems.

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Delphacodes kuscheli Fennah (Hemiptera: Delphacidae) is the main natural vector of Mal de Rio Cuarto virus (family Reoviridae, genus Fijivirus, MRCV), which infects different gramineae and causes the most important maize (Zea mays L.) disease in Argentina. MRCV—vector interactions usually are studied using different winter cereals as hosts. Under experimental conditions, <50% of D. kuscheli planthoppers fed on a MRCV-infected plant can transmit the virus to wheat (Triticum aestivum L. ). This fact is influenced by insect development stage at acquisition and the latency period. This work describes the relation between transmission efficiency and MRCV accumulation in its planthopper vector. First- and third-instar D. kuscheli nymphs were allowed to feed on MRCV-infected plants, and 9 or 17 d after the acquisition access period (AAP), viral load of transmitting and nontransmitting planthoppers was quantified by quantitative polymerase chain reaction. The transmitting planthoppers showed significantly higher viral titers than nontransmitting ones, suggesting that successful transmission is positively associated to viral accumulation in the insect. However, planthoppers of the third-instars group did not transmit the virus 9 d after AAP, even when 46% had similar titers to the transmitting insects of the other treatments. These results indicate that additional factors influence MRCV transmission efficiency when acquisition occurs in older planthoppers. This is the first precise quantitative analysis of MRCV in its main vector species and will definitely contribute to better understand planthopper—Fijivirus interactions and its epidemiological implications.

The wheat curl mite, Aceria tosichella Keifer (Acari: Eriophyidae), is reported for the first time in South America from Argentina. Aceria tosichella specimens were collected from Wheat Streak Mosaic Virus-infected wheat plants from Buenos Aires Province. The risk of dissemination of this eriophyid mite into unaffected neighboring countries of South America and need to adopt quarantine measures to avoid its dissemination are discussed.

<p class="normal">En ambientes severos, la presencia de hongos micorrícicos arbusculares (HMA) es clave para la supervivencia de las plantas y el balance ecosistémico. El objetivo de este trabajo fue caracterizar los hongos micorrícicos presentes en sitios de algarrobales (<em>Prosopis alba</em>) del Parque Chaqueño argentino de condiciones climáticas contrastantes: húmedo, Colonia Benítez, y semiárido, Padre Lozano. Los sitios de Colonia Benítez y Padre Lozano presentaron diferencias edafológicas significativas, destacándose el menor contenido de materia orgánica y fósforo, y el mayor porcentaje de sodio intercambiable en Colonia Benítez, asociados a una mayor capacidad infectiva y mayor potencial micorrícico de inóculo. En los suelos sólo se encontró una especie común: <em>Acaulospora laevis</em>, propia de ambientes áridos. En los inóculos se registraron tres especies en común: <em>Funneliformis mosseae</em>, <em>Rhizophagus intraradices</em>, <em>Claroideoglomus</em> <em>etunicatum</em>; dos especies exclusivas de Colonia Benítez, <em>Septoglomus constrictum </em>y <em>Rhizophagus clarus</em>; y dos especies exclusivas de Padre Lozano, <em>Claroideoglomus claroideum</em> y <em>Diversispora spurca</em>. Este es el primer estudio en Argentina en el cual se reporta la diversidad de HMA en suelos de algarrobales y se mide la infectividad de los suelos y de los inóculos obtenidos a partir de esos suelos.</p>

Breeding selection of germplasm under fertilized conditions may reduce the frequency of genes that promote mycorrhizal associations. This study was developed to compare variability in mycorrhizal colonization and its effect on mycorrhizal dependency (MD) in improved soybean genotypes (I-1 and I-2) with differential tolerance to drought stress, and in unimproved soybean genotypes (UI-3 and UI-4). As inoculum, a mixed native arbuscular mycorrhizal fungi (AMF) was isolated from soybean roots, showing spores mostly of the species Funneliformis mosseae. At 20 days, unimproved genotypes followed by I-2, showed an increase in arbuscule formation, but not in I-1. At 40 days, mycorrhizal plants showed an increase in nodulation, this effect being more evident in unimproved genotypes. Mycorrhizal dependency, evaluated as growth and biochemical parameters from oxidative stress was increased in unimproved and I-2 since 20 days, whereas in I-1, MD increased at 40 days. We cannot distinguish significant differences in AMF colonization and MD between unimproved and I-2. However, variability among improved genotypes was observed. Our results suggest that selection for improved soybean genotypes with good and rapid AMF colonization, particularly high arbuscule/hyphae ratio could be a useful strategy for the development of genotypes that optimize AMF contribution to cropping systems.

Prosopis alba Griseb. (algarrobo blanco) is an important tree legume in semiarid regions of South America. Under field conditions, their seedlings are subjected to a wide range of environmental conditions that might produce stress, reducing their survival and/or growth. The aim of this work was to evaluate the combined effect of two native arbuscular mycorrhizal fungi (AMF) inocula and fertilization on growth variables of P. alba seedlings under nursery conditions and after drought stress. P. alba seedlings received different levels of basic fertilization (0%, 25% and 100%) and were inoculated with native AMF isolated from different rainfall regions of Parque Chaqueño Argentino: Colonia Benítez (CB, 1300 mm rainfall) and Padre Lozano (PL, 650 mm rainfall) or a mixture of both inocula (MIX), while the control group remained uninoculated. The combined application of native AMF and fertilization did not affect mycorrhizal colonization but allowed the formation of the different AMF structures. Moreover, when comparing the PL inoculum from a low rainfall region with other treatments, it significantly increased growth and development under nursery conditions and drought stress tolerance in the greenhouse. Therefore, AMF benefits for P. alba were related to inoculum source, being improved by the application of low fertilizer rates. This work supports the development of sustainable P. alba seedlings production and their field establishment under symbiotic conditions with native AMF.Keywords ''Algarrobo blanco'' Á Mineral nutrition Á Mycorrhizae Á Nursery Á Water stress

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