Comparative transmission of two cucumber mosaic virus isolates by two color morphs of Acyrthosiphon pisum (Harris)

 Cucumber mosaic virus (CMV) is one of the most important legume-infecting viruses, which is transmitted effectively by pea aphid Acyrthosiphon pisum (Harris) (Hem: Aphididae). Transmission efficiency of two CMV isolates (As and Kh from cowpea and bean hosts, resp.) by red and green color morphs of pea aphid were evaluated on bean plants. Triple-antibody sandwich ELISA (TAS-ELISA) using CMV-specific monoclonal antibodies revealed that both CMV isolates belonged to the serotype II. Bean plants inoculated by viruliferous aphids were assayed by double-antibody sandwich ELISA (DAS-ELISA) at 16 days post inoculation (dpi). The results showed that the transmission rate of CMV-As by the red morph was significantly higher than by the green morph, resulting in significantly higher transmission rate of the virus (As + Kh) by the red morph than by the green morph, with p≤ 0.1. Similarly, the efficiency of CMV transmission by the red morph of A. pisum was higher than the efficiency of transmission by the green morph. The higher transmission rate and efficiency of CMV by red pea aphid would be important in the epidemiology. Based on these results, we hypothesize that the transmission efficiency of CMV is affected more by the difference in transmission determinants of A. pisum color morphs than by the sequence of virus coat protein determinants.

KEYWORDS

Aphididae; Bromoviridae; color polymorphism; transmission efficiency.

Carnation mottle virus, an important viral agent infecting carnation cut-flower crops in Mahallat of Iran

One of the most important cut-flower crops grown worldwide on commercial scale is Carnation (Dianthus caryophyllus L.). It's the main production of Mahallat where is one of the most important ornamental plants production centers of Iran. Infection of carnation with pathogens Like viral agents causes economic losses in carnation cut-flower crop. One of the viral agents of this flower is Carnation mottle virus (CarMV) which is the type member of genus Carmovirus and belongs to the Tombusviridae family. It is naturally transmitted by grafting and contacting between plants. Although its infection lead to mild symptims, it weakens the plant to infection by other pathogens. The carnation greenhouses of Mahallat were visited during 2008 January to April and 100 samples with mild mosaic symptom were collected and tested by DAS-ELISA using CarMV specific polyclonal antibody. The results showed that 75% of samples wrere infected with this virus. Mechanical inocubation of Chenopodium quinoa, C. amaranticolor and Spinacea oleracea with extracted crude sap of CarMV infected carnation Leaves in phosphate buffer (pH, 7) resulted in appearance of chlorotic and necrotic local lesions on inoculated leaves 4-7 days after incubation. The virus was partially purified using C. amaranticolor locally symptomatic leaves. Total soluble proteins were extracted from healthy and CarMV infected C. amaranticolor plants and beside partially purified preparation electrophoresed through 15% poly acrylamide get according to SDS-PAGE standard procedure. Protein bands were electroblotted onto nitrocelluse membrane and incubated with CarMV polyclonal during western immunoblot analysis according to standard method. The result revealed a distinc protein band with Mr of 35.5 kDa in total protein preparation of infected plant and viral partial pure preparation, without any reaction in those of healthy plant. RT-PCR carried out using total RNA extracted from infected plant by Rneasy Plant Mini Kit (Qiagen)and a pair of primers, CPu, CPd, corresponding to the flanking region of the virus CP resulted in amplification of a DNA fragment in expected size around 1 kbp.

Characterisation of lettuce virus X, a new potexvirus infecting lettuce in Iran

A virus with flexuous rod-shaped particle morphology was found in samples from lettuce during a survey of viruses infecting lettuce in Tehran province in Iran. This virus was subjected to a complete analysis of its biological and molecular features. The entire nucleotide sequence of the virus was determined, revealing a polyadenylated ssRNA genome consisting of 7,212 nucleotides [without poly (A) tail] and possessing an organization typical for potexviruses. Comparative genome analysis showed that the lettuce virus is closely related to Alstroemeria virus X, narcissus mosaic virus and asparagus virus 3. Based on particle morphology, physico-chemical properties and the complete genome sequence, this virus is a member of a new species in the genus Potexvirus, for which the name lettuce virus X (LeVX) is proposed. Biological assays using an infectious cDNA clone and a wild-type isolate of LeVX revealed that the virus, despite reaching high concentrations in all lettuce cultivars tested, does not cause symptoms in lettuce.