Incidence and Geographic Distribution of Sweet Clover Necrotic Mosaic Virus in Alberta
1986; American Phytopathological Society; Volume: 70; Issue: 12 Linguagem: Inglês
10.1094/pd-70-1129
ISSN1943-7692
Autores Tópico(s)Plant Pathogens and Resistance
Resumowas removed with minimum disturbance. Hiruki, C. 1986. Incidence and geographic distribution of sweet clover necrotic mosaic virus in The plants were grown in the greenhouse Alberta. Plant Disease 70: 1129-1131. for further observation and testing. ELISA. Antiserum to SCNMV was During a survey period from 1979 to 1983, sweet clover necrotic mosaic virus (SCNMV), a member produced as reported previously (11). of the dianthovirus group, was found widespread in the central and northern areas of Alberta Basic procedures for ELISA were the where major soil types are black soil and dark gray soil, respectively. In these areas, SCNMV same as those reported earlier (3). The occurred predominantly on sweet clover; the only exception was a SCNMV variant found on absorbance values were read at 405 nm alfalfa (Medicago sativa). The virus was not detected in alsike clover (Trifolium hybridum), red on a Titertek Multiskan (Flow Laboraclover (T. pratense), white clover (T. repens), and crown vetch (Coronilla varia) growing in the areas where the virus was prevalent. Root and leaf infection occurred when sweet clover seedlings tories, Mississauga, Ontario). were dip-inoculated in a virus suspension or inoculated by pouring virus inoculum around the Vector transmission. For Olpidium seedlings. The presence of Olpidium brassicae zoospores in the inocula caused no significant transmission, a virus-free culture of differences in SCNMV infection rates. Sweet clover weevil (Sitona cylindricollis) was found Olpidium brassicae (Wor.) Dang. infesting both SCNMV-infected and uninfected sweet clovers (Melilotus officinalis and M. alba). established previously (6) was used in this When virus-free S. cylindricollis was fed on SCNMV-infected sweet clover for 5-10 min, the virus investigation. Methods of maintaining was detected in the head, body, and feces. However, weevil transmission experiments to young and testing the Olpidium culture and test sweet clover seedlings were unsuccessful. plant seedlings were the same as those described previously (7). Dip- or pourinoculations with virus suspensions (1 Sweet clover is an introduced species necrotic mosaic virus (SCNMV) (10). In mg/ml), in the presence (1 X 106 that was reported growing in North this paper, the results of investigations on zoospores per milliliter) or in the absence America as early as 1739. Its value as a virus distribution in Alberta and on virus of zoospores, were made using 10-dayforage crop has been recognized since transmission are reported. old sweet clover seedlings. Assays of both 1875. It is a fast-growing legume that is inoculated and uninoculated seedlings valuable for land reclamation and soil MATERIALS AND METHODS were performed by ELISA 1,2, and 3 wk improvement, hay and silage production, Virus. The virus used as an immunogen after inoculation, using root and leaf and nutritious pasturage. It is also useful was originally isolated from sweet clover, samples. At the same time, root samples as a source of nectar and pollen for subjected to several single-lesion transfers were examined microscopically for honeybees and is important for the in Phaseolus vulgaris L. 'Red Kidney,' Olpidium infection. For insect transproduction of high-quality honey (5). and further multiplied in the same host or mission, sweet clover weevils (Sitona Sweet clover, a biennial crop in short in Nicotiana clevelandii Gray. cylindricollis Fbhraeus) were collected in rotations, is well adapted to the dry Test plants. For routine assay of field the field. After a fasting period of at least conditions of western Canada. It is specimens, about 50-60 samples were 3 days, they were kept on healthy sweet winter-hardy and productive, especially tested at a time. Chenopodium clover plants. In certain experiments, the on fertile, well-drained clay and clay- amaranticolor Coste & Reyn., weevils were used directly after the loam soils. However, it has also adapted Gomphrena globosa L., and P. vulgaris fasting period. Assays for SCNMV were successfully to sandy loams and heavy L. 'Red Kidney' were used for virus performed by ELISA, using extracts of clay loams as well as Gray Luvisol soils. recovery and identification of the virus, test plants and insects. It grows best on neutral or alkaline soils Growth conditions. All plants were and is one of the best legumes to grow on grown in 12-cm-diameter pots containing RESULTS highly alkaline soils (1). an autoclaved mixture of loam, sand, and Sensitivity of virus assay methods. In 1979, an unidentified virus was peat (3:2:1l, v/ v), at 25 ± 2 C. Before using ELISA for detecting discovered infecting yellow-blossomed Collection of field samples. We SCNMV in field specimens, we established sweet clover plants (Melilotus officinalis collected the samples at the edge of the that under the present experimental Lam.) in the Athabasca area (10) and was field and in the crop stand by walking in a conditions, ELISA was capable of later found elsewhere in Alberta infecting crisscross manner. Samples were also detecting 10 ng of SCNMV antigen. In a M. alba Medik. Diseased plants showed collected from sweet clover plants comparison of results from inoculation ringspot and systemic veinal necrosis growing on the road shoulders and tests and from ELISA, in more than associated with mosaic, and virus banks. Young shoots with a few leaves 1,000otests performed, there was complete infection resulted in pronounced reduction were cut and placed in a plastic bag. A agreement between them, except for one in foliage growth. The causal virus was series sample number was assigned and a alfalfa isolate that was initially not characterized and named sweet clover record made of the exact location and detected by ELISA. symptoms observed. The samples were Virus distribution. SCNMV infection tested within 1-2 days of sampling by sap of sweet clover caused systemic necrosis
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