Cytopathological characterization of Mal de Río Cuarto virus in corn, wheat and barley

Abstract

The Mal de Río Cuarto disease is caused by Mal de Río Cuarto virus (MRCV) transmitted by Delphacodes kuscheli. Comparative studies were carried out on the cytopathological alterations produced by MRCV in corn (Zea mays), wheat (Triticum aestivum) and barley (Hordeum vulgare), as seen with a transmission electron microscope. Corn plants were infected with viruliferous D. kuscheli collected from the endemic disease area (i.e. Río Cuarto County, Córdoba, Argentina). For the viral transmission to small grain cereal plants, laboratory rared insects were used. In this case, the inoculum source was wheat and barley plants infected with MRCV isolate grown in a greenhouse. Leaf samples with conspicuous symptoms were collected: enations and size reduction in corn; crenatures, swelling veins and dark green color in small grain cereals. Viral infection was corroborated by DAS-ELISA. Viroplasms containing complete and incomplete virus particles and fibrillar material were found in the cytoplasm of infected cells in all species. Mature virions were between 60 and 70 nm diameter. In wheat and barley, viroplasms and dispersed particles were observed only in phloem, while in corn virions were also found in cells of the bundle sheath. Crystalline arrays of particles were detected in corn enation constitutive cells. Tubular inclusions were found only in wheat samples. The three species showed abnormalities in the chloroplasts of affected cells. The results showed that MRCV cytopathology has similarities with other viruses from the genus Fijivirus, family family Reoviridae, but slight differences depending upon the host plant.

Feeding behavior of the vectorDelphacodes kuscheli(Hemiptera: Fulgoromorpha: Delphacidae) on maize and oat

“…Th is result reveals a less eff ective feeding behavior on this host and is consistent with demographic studies on fi eld and laboratory reported by which indicate the non-preference of D. kuscheli feeding and reproduction on maize. Likewise, these results could explain the observations of Arneodo et al (2002b) who detected viroplasms and dispersed MRCV particles only inside the phloem (parenchyma cells cytoplasm, sieveelements and companion cells), on wheat (Triticum aestivum) and barley (Hordeum vulgare); whereas, in infected maize leaves, viral particles were found outside the phloem, in the bundle sheath cells that surround the vascular region. Furthermore, the feeding behavior of D. kuscheli observed on maize might explain the low transmission rate of MRCV reported on this species by Ornaghi et.…”

Caenodelphax teapae (Fowler) (Hemiptera: Delphacidae): nuevo vector natural del Mal de Río Cuarto virus (MRCV, Fijivirus) en Argentina

“…Las características y el tamaño de las partículas observadas fueron similares a las descriptas por otros autores para el MRCV (Nome et al, 1981;Truol et al, 2001;Arneodo et al, 2002b).…”

“…Posteriormente fueron teñidos con acetato de uranilo al 2% y citrato de plomo y observadas en un microscopio electrónico de transmisión JEOL JEM 1200 EX II en magnificaciones de 10000X. La presencia de partículas virales y posibles alteraciones fueron analizadas y comparadas con las alteraciones descriptas para diversos aislamientos del MRCV (Nome et al, 1981;Arneodo et al, 2002b).…”

“…El principal vector del MRCV en la naturaleza es Delphacodes kuscheli Fennah (Remes Lenicov et al, 1985). Este virus, al igual que otros miembros del grupo, se halla confinado al tejido floemático de las plantas infectadas (Nome et al, 1981;Truol et al, 2001;Arneodo et al, 2002b) y luego que ha sido adquirido por D. kuscheli, el vector permanece infectivo (transmisor) y es capaz de transmitirlo hasta su muerte (Arneodo et al, 2002a). Esta capacidad de transmitir que adquiere el insecto se denomina infectividad.…”

Mal de Río Cuarto virus (MRCV) genomic segment S3 codes for the major core capsid protein

“…Complete particles are about 65 nm in diameter and have a dark core surrounded by a less contrasted region. Incomplete particles (or ''empty'' inner capsids not filled with nucleic acids) form large masses [16,17]. Unlike plant-infecting viruses of other genus of the Reoviridae family, very little is known about the function and localization of Fijivirus structural and nonstructural proteins [18][19][20][21][22][23][24].…”