Serological survey of virus in cucurbit species in the Lower Middle São Francisco River Basin, BrazilAiming to get information about the virus that most frequently infects cucurbit plants of the species Benincasa hispida, Citrullus spp., Cucurbita spp., Cucumis melo, Lagenaria sp., Momordica charantia and also some F 1 hybrids of C. lanatus with C. lanatus var. citroides in irrigated areas of Petrolina-PE and Juazeiro-BA, experimental and farming areas were surveyed in the first and second half of each year (2005 to 2007). The samples were tested by indirect enzyme-linked immunosorbent assay (ELISA) against antisera specific for Papaya ringspot virus, type watermelon (PRSV), Watermelon mosaic virus (WMV), Zucchini yellow mosaic virus (ZYMV) and Cucumber mosaic virus (CMV), and by Agar Double Diffusion against antiserum specific for Squash mosaic virus (SqMV) at the Plant Virus Laboratory of the Federal University of Ceará. Leaf samples from 967 plants were analyzed and 608 of them were infected. Among 125 samples from symptomless plants, 42 allow replication. PRSV-W was predominant, followed by WMV and ZYMV, and mixed infections occurred in all infected species. CMV was detected only in one sample and SqMV was not found. This is an indication that a breeding program for virus resistance in cucurbit species in the region must consider the three potyviruses. Keywords: Citrullus lanatus, Cucumis melo, Serology, Potyvirus, mixed infection.Entre as famílias de plantas utilizadas para a produção de alimentos, as cucurbitáceas ocupam lugar de destaque em importância econômica e social, em particular para o Nordeste brasileiro onde seu cultivo é praticado por pequenos produtores em regime de agricultura familiar. Por outro lado, nessa região, as cucurbitáceas são também exploradas por empresas exportadoras de frutas. Entre as cucurbitáceas de importância econômica para o Nordeste brasileiro destaca-se o melão (Cucumis melo L.), sendo a região a maior produtora nacional, com a produção concentrada nos estados do Rio Grande do Norte e Ceará, a melancia [Citrullus lanatus (Thunb.) Matsum. & Nakai] e as abóboras (Cucurbita spp.), produzidas em toda região. Nessa região, onde as empresas produtoras e exportadoras de frutas utilizam da irrigação, um grande volume dessas e outras cucurbitáceas é produzido por pequenos produtores em condições de sequeiro. Esses cultivos apresentam variabilidade genética para vários caracteres que podem ser utilizadas no melhoramento das culturas. As variedades utilizadas nos cultivos irrigados não foram desenvolvidas 123 Tropical Plant Pathology 34 (2)
Papaya (Carica papaya) is an important tropical fruit crop in northeastern Brazil. Lethal yellowing is a disease caused by Papaya lethal yellowing virus (PLYV) that occurs only in northeastern Brazil. The symptoms are characterized by progressive leaf yellowing and greenish circular spots on the fruits. The virus has isometric particles (30 nm), genomic single-stranded (ss)RNA (1.6 × 106 Da), and a coat protein with a single component (35 kDa). Although no biological vector has been confirmed, the virus is spreading every year. In the present study, an isolate of the virus was characterized biologically, serologically, physically, and molecularly, and its survival in dried tissue was evaluated. Approximately 309.5 mg of virus was purified per kilogram of infected papaya leaves, and a high-titer polyclonal antiserum (1:1,024,000) was obtained from an immunized rabbit. The virus was detected in dried roots and leaves maintained up to 120 days. Its physical properties were thermal inactivation point (80°C), longevity in vitro (60 days), and dilution end point (10-6). The virus was inactivated in leaves and roots eradicated from infected plants when they were submitted to a solarization period of 12 days, but maintained its infectivity when leaves and roots were maintained over the soil at natural conditions for 32 days. Among 58 plant species from 13 botanical families, the PLYV isolate infected only C. papaya, Jacaratia heterophylla, J. spinosa, Vasconcella cauliflora, V. quercifolia, and V. monoica, all from the family Caricaceae. A fragment of 1,098 nt of the virus isolate, corresponding to the 3′ replicase (RdRp) and 5′ coat protein (CP) cistron, was cloned and sequenced. Phylogenetic analysis of the RdRp nucleotide sequences indicated some similarity of PLYV with members of the genus Sobemovirus.
Amostras foliares de Crotalaria paulinea apresentando mosaico foram coletadas em São Luiz, MA, e enviadas ao Laboratório de Virologia Vegetal da UFC. As amostras foram testadas por Elisa indireto, contra anti-soros para Cowpea aphid-borne mosaic virus (CABMV) e Cucumber mosaic virus (CMV) e por dupla difusão em àgar contra anti-soro para Cowpea severe mosaic virus (CPSMV). As amostras reagiram somente com o anti-soro para CPSMV, indicando ser C. paulinea mais um hospedeiro natural do vírus. Extratos das folhas de C. paulinea foram inoculados em plantas de caupi (Vigna unguiculata subsp. unguiculata) mantidas em casa de vegetação. Dez dias após a inoculação, as plantas passaram a exibir sintomas de mosaico e a presença do CPSMV foi confirmada por sorologia. Nos estudos de gama de hospedeiros, envolvendo oito espécies botânicas, o isolado de CPSMV obtido de C. paulinea (CPSMV-Cp) infetou sistemicamente somente cultivares de caupi. Estudos de reações de RT-PCR revelaram a presença de uma banda no gel de agarose de 594 pb para o CPSNV-Cp semelhante às de outros isolados de CPSMV. O CPSMV-Cp foi multiplicado em caupi cv. Pitiúba e purificado por clarificação com n-butanol, precipitação viral com PEG e ultracentrifugação. A preparação purificada apresentou um espectro de absorção ultravioleta típico de núcleoproteína com uma razão A260/A280 de 1,7. Coelho da raça Nova Zelândia Branca imunizado com a preparação viral purificada, produziu anti-soro policlonal reativo com CPSMV em dupla difusão em àgar. Este é o primeiro relato sobre a infecção natural de CPSMV em C. paulinea.
No abstract
The Northeastern Brazil has a great potential for production of melon (Cucumis melo) and watermelon (Citrullus lanatus). More than 20 virus species have been found naturally infecting cucurbit species around the world, but only seven of them were already found infecting those cucurbit crops in Northeastern Brazil. Plant viruses have been identified by several methods involving their morphological, physical, biological, cytological, serological and molecular properties, but serology is one of the most specific and accessible methods to obtain a rapid and precise diagnosis of a plant disease caused by virus. Several serological techniques were developed and the advent of the enzyme-linked immunosorbent assay (ELISA) has facilitated the use of serology in the identification and characterization of plant viruses, including those infecting melon and watermelon. Virus infections in melon and watermelon are considered of great importance because they can seriously affect yield all over the world, mainly in developing countries. The present review describes biological, morphological, serological and molecular properties of important virus species infecting melon and watermelon in commercial fields of Northeastern Brazil. The review covers the virus species from the following family and genera: Potyviridae
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