Amplifier Hosts May Play an Essential Role in Tomato Begomovirus Epidemics in Brazil.

Current control of tomato golden mosaic disease, caused in Brazil predominantly by tomato severe rugose virus (ToSRV), is dependent on both, planting resistant/tolerant hybrids and intensive insecticide sprays (two to three per week) for controlling Bemisia tabaci, the vector of ToSRV. Resistant hybrids only confer moderate resistance to infection by ToSRV and some tolerance to the disease. Insecticide sprays, although widely used, have failed in most tomato production areas in Brazil, as they are unable to reduce primary spread, i.e., infection caused by the influx of viruliferous whiteflies coming from external sources of inoculum. Severe epidemics are recurrently observed in some tomato fields in several Brazilian regions, which prompted us to postulate the existence in the agroecosystem, in some places and time, of amplifier hosts that provide the necessary force of infection for epidemics to occur, even in the absence of secondary spread in the target crop. Amplifier hosts are ideally asymptomatic, occur in high density near the target crop, and support growth of both virus and vector. Soybean and common bean are potential amplifier hosts for begomovirus in tomato crops. Our results support the hypothesis that soybean plants may play an important role as an amplifier host of ToSRV for tomato crops in the field, although this does not seem to be a frequent phenomenon. Successful amplification will depend on several factors, including the soybean cultivar, the soybean stage of development at the moment of infection, the ToSRV isolate, and the perfect synchrony between the beginning of a soybean field and the end of a ToSRV-infected crop, and, later, between the senescence of the ToSRV-infected soybean plants and the new tomato crop. The concept of amplifier hosts has been widely used in ecology of zoonoses but, to our knowledge, has never been used in botanical epidemiology.

Rearing Frankliniella zucchini Nakahara & Monteiro (Thysanoptera: Thripidae) on zucchini (Cucurbita pepo L. 'Caserta') fruits

Abstract Frankliniella zucchini transmits zucchini lethal chlorosis virus, causal agent of lethal chlorosis of zucchini squash. The characteristics of relationship between this virus with its vector have not been studied, one of the reasons being the lack of a method for rearing the thrips for laboratory studies. This work proposes a system for the rearing of F. zucchini on fresh virus free zucchini 'Caserta' fruits, offering a practical and efficient alternative for the supply of a large number of insects for later study of virus/vector relationship. In addition, to aid in the identification of this species of thrips, the immature and adult forms obtained from the colony were described.

Expanding Knowledge of the Host Range of Tomato chlorosis virus and Host Plant Preference of Bemisia tabaci MEAM1.

The crinivirus Tomato chlorosis virus (ToCV) is often found infecting tomato crops in Brazil, with variable incidence, but associated with prevalence of its primary vector, Bemisia tabaci MEAM1. ToCV control is difficult because there are no resistant commercial tomato varieties or hybrids available and chemical spray for control of the whitefly vector has not been effective. The present study evaluated the partial host range of a Brazilian isolate of ToCV and the preference of B. tabaci MEAM1 for oviposition on those species identified as susceptible to the virus. Subsequently, transmission tests were performed using plants of each ToCV host species as sources of inoculum to elucidate the epidemiological importance of nontomato sources of inoculum for infection of tomato. Among 80 species experimentally inoculated, 25 were susceptible, including 6 previously not known to be hosts (Jaltomata procumbens, Physalis pruinosa, Solanum aculeatissimum, S. viarum, Beta vulgaris var. cicla, and Chenopodium quinoa). Preference of whitefly for oviposition and infection by ToCV under free-choice transmission tests varied among the susceptible species. When ToCV-infected tomato, eggplant, and C. quinoa were used separately as sources of inoculum for virus transmission to tomato plants, mean percentages of infected plants were 76.6, 3, and 0%, respectively. Average oviposition of Bemisia tabaci on these three hosts were 2.7, 10.6, and 0.0 eggs/cm2, respectively. Additional studies will be necessary to evaluate the importance of ToCV host plants under field conditions and their efficiency as sources of inoculum for virus acquisition and transmission to tomato crops.

Biological and molecular characterization of a putative new potexvirus infecting Senna occidentalis.

In this work, we report the complete genome sequence of, production of polyclonal antibodies against, and development of biological assays for a putative new potexvirus, named senna mosaic virus (SenMV), found infecting Senna occidentalis in the state of São Paulo, Brazil. The complete genome sequence of SenMV comprises 6775 nucleotides excluding the poly(A) tail. The genome organization is similar to those of other potexviruses, with five open reading frames coding for RNA-dependent RNA polymerase (RdRp), the triple gene block (TGB 1, 2, and 3) proteins, and coat protein (CP). The virus was transmitted to S. occidentalis by mechanical inoculation and trimming scissors, but not by seeds.

Genome organization and host range of a Brazilian isolate of johnsongrass mosaic virus.

This work reports the complete genome sequence, production of a polyclonal antiserum, and host range of a Brazilian strain of johnsongrass mosaic virus (JGMV) found infecting Panicum maximum in the state of São Paulo, Brazil. The complete genome sequence of this potyvirus, comprising 9874 nucleotides, showed 82 % amino acid sequence identity in the polyprotein to that of an isolate of JGMV from Australia. The experimental host range of this virus included mainly fodder species. Cultivated species such as rice, oats, sugarcane, rye, corn and wheat were not infected, suggesting that current isolates of this potyvirus do not represent a threat to these crops in Brazil.

Genetic Transformation of Passionflower and Evaluation of R1 and R2 Generations for Resistance to Cowpea aphid borne mosaic virus.

We report on the production and evaluation of passionflower transgenic lines for resistance to Cowpea aphid borne mosaic virus (CABMV). Genetic transformation was done using Agrobacterium tumefaciens and transgene integration was confirmed by Southern blot analyses, resulting in nine transgenic lines for 'IAC 275' and three for 'IAC 277'. Transgenic lines were clonally propagated and evaluated for resistance to CABMV. After the third inoculation, under higher inoculum pressure, only propagated plants of the transgenic line T16 remained asymptomatic, indicating a high resistance to infection with CABMV. This transgenic line was self-pollinated and the R1 generation was evaluated together with the R1 generation of another resistant transgenic line (T2) identified previously. Plants were inoculated with CABMV by means of viruliferous Myzus nicotianae. All 524 T2R1 plants became infected, whereas 13 of 279 T16R1 remained asymptomatic after four successive inoculations. A T16R2 generation was obtained and plants were inoculated with CABMV mechanically or by aphids. After successive inoculations, 118 of 258 plants were symptomless, suggesting that the resistance to CABMV was maintained in the plant genome as the homozygous condition was achieved. Five selected resistant T16R2 plants which contained the capsid protein gene are being crossed for further analyses.

First report and differential colonization of Passiflora Species by the B biotype of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) in Brazil / Primeiro relato e colonização diferencial de espécies de Passiflora pelo biótipo B de Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) no Brasil

This note is the first report of Bemisia tabaci (Gennadius) biotype B colonizing passionvine in Brazil. We examined the colonization of nine Passiflora species by a wild B type population under greenhouse conditions. P. amethystina Mikan was the most preferred species for oviposition and colonization, whereas P. suberosa L., P. coriacea Juss. and two commercially cultivated species, P. alata Curtis and P. edulis Sims f. flavicarpa Degener, were mostly uncolonised. P. morifolia Mast., P. cincinnata Mast., P. foetida L. and P. caerulea L. showed intermediate levels of colonization. Such differential colonization might suggest some degree of resistance by certain Passiflora species or oviposition preference by B. tabaci.

Esse trabalho descreve pela primeira vez a ocorrência do aleirodídeo Bemisia tabaci (Gennadius) biótipo B colonizando maracujazeiros no Brasil. Também foi examinada a colonização de nove espécies de Passiflora pelo inseto em condições de telado. P. amethystina Mikan foi a espécie de maior preferência para oviposição e colonização, enquanto P. suberosa L., P. coriacea Juss. e duas espécies cultivadas comercialmente, P. alata Curtis e P. edulis Sims f. flavicarpa Degener, foram pouco colonizadas pelo aleirodídeo. P. morifolia Mast., P. cincinnata Mast., P. foetida L. e P. caerulea L. exibiram níveis intermediários de colonização. Esses resultados sugerem que certas espécies de Passiflora exibem diferentes graus de resistência à colonização ou preferência para oviposição de B. tabaci biótipo B.

First report and differential colonization of Passiflora species by the B biotype of Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) in Brazil.

This note is the first report of Bemisia tabaci (Gennadius) biotype B colonizing passionvine in Brazil. We examined the colonization of nine Passiflora species by a wild B type population under greenhouse conditions. P. amethystina Mikan was the most preferred species for oviposition and colonization, whereas P. suberosa L., P. coriacea Juss. and two commercially cultivated species, P. alata Curtis and P. edulis Sims f. flavicarpa Degener, were mostly uncolonised. P. morifolia Mast., P. cincinnata Mast., P. foetida L. and P. caerulea L. showed intermediate levels of colonization. Such differential colonization might suggest some degree of resistance by certain Passiflora species or oviposition preference by B. tabaci.

Transmissão do Passion fruit woodiness Virus por Aphis gossypii ( Glover ) ( Hemiptera: Aphididae ) e colonização de maracujazeiro pelo vetor / Transmission of Passion fruit woodiness virus by Aphis gossypii ( Glover ) ( Hemiptera: Aphididae ) and colonization of Passion flower by the vector

Avaliou-se a transmissão de Passion fruit woodiness virus (PWV) por Aphis gossypii (Glover). Em dois experimentos independentes, o afídeo transmitiu o PWV para maracujazeiros com taxas de 75 por cento e 100 por cento, ao se depositarem oito e doze afídeos virulíferos por planta, respectivamente. No final dos testes, observaram-se, em algumas plantas de maracujá, formas ápteras e ninfas de A. gossypii, sugerindo a colonização dessas plantas pelo afídeo. Esse parece ser o primeiro relato da colonização de Passiflora edulis f. flavicarpa (Deneger) por uma espécie de afídeo.

A new eriophyid mite-borne membrane-enveloped virus-like complex isolated from plants.

A decade ago, a new mite-transmitted disease was described on wheat (Triticum aesativum) and maize (Zea mays) that due to its geographical location was referred to as High Plains Disease (HPD). To determine the etiology, we established colonies of HPD pathogen-transmitting eriophyid wheat curl mites (Aceria tosichella) on wheat plants for maintenance of a continuous source of infected material. Analyses of nucleic acid obtained from infected plants showed the presence of HPD-specific RNAs ranging from 1.5 to 8 kilobases, but comparisons between the sequence of cDNAs and the databases did not reveal any clear identity with known viruses. We demonstrate that a diagnostic HPD-specific 32-kDa protein that accumulates in plants is encoded by a small RNA species (RNA-s). Upon infestation of upper wheat parts with viruliferous mites, the RNA-s encoded protein becomes detectable within a few days in the roots, indicative of an effective virus-like mode of transport. Membranous particles, resembling those observed in thin sections of infected plants, were isolated and shown to envelope a thread-like ribonucleoprotein complex containing the RNA-s encoded 32-kDa protein. This complex was associated with single-stranded (-)-sense RNAs, whereas free (+)-sense RNA was only detected in total RNA of infected plants. Based on the collective properties, we conclude that HPD is caused by a newly emerged mite-borne virus, for which we propose the name Maize red stripe virus (MRStV).

[Transmission of Passion fruit woodiness virus by Aphis gossypii (Glover) (Hemiptera: Aphididae) and colonization of passion flower by the vector]. / Transmissão do Passion fruit woodiness virus por Aphis gossypii (Glover) (Hemiptera: Aphididae) e colonização de maracujazeiro pelo vetor.

The transmission of Passion fruit woodiness virus (PWV) by Aphis gossypii (Glover) was evaluated. In two independent experiments, A. gossypii transmitted PWV to passion fruit plants at the rates of 75% and 100%, when eight and twelve viruliferous aphids were deposited by plant, respectively. At the end of the tests, nymphs of A. gossypii were observed in some of the passion fruit plants, suggesting that the aphid species was colonizing the plants. This seems to be the first report of Passiflora edulis f. flavicarpa (Deneger) colonization by a species of aphid.

Host-specific generation and maintenance of Tomato bushy stunt virus defective interfering RNAs.

The accumulation of Tomato bushy stunt virus (TBSV) defective interfering RNAs (DIs) has been observed in several species of plants, but the involvement of host-specific processes and the functional role of DIs are still poorly understood. In this study, the accumulation of DIs was compared after several passages of TBSV through Nicotiana benthamiana and pepper (Capsicum annuum). As anticipated, passages of wild-type TBSV through N. benthamiana resulted in the accumulation of significant levels of TBSV DIs, which caused symptom attenuation and prevented the plants from lethal necrosis. On the contrary, TBSV infection of pepper plants caused severe local and systemic chlorosis, but continuous virus passages did not result in detectable levels of DIs accumulation. In addition, the inoculation of pepper plants with a mixture of helper virus and DI either from in vitro generated transcripts or from infected N. benthamiana did not yield DI in upper pepper leaves. Our cumulative results suggest that complex host-specific determinants play an important role in TBSV DI generation and their subsequent maintenance and accumulation.