RESUMO
Rice stripe necrosis virus (RSNV) was first described in 1977 as a new virus infecting rice in Cote d'Ivoire (3) and was subsequently observed in Liberia, Nigeria, and Sierra Leone (2). RSNV is a soil-borne virus transmitted by the fungus Polymyxa graminis (1) and belongs to the genus Benyvirus (4). During a survey carried out in April of 2013, severe symptoms characterized by seedling death, severe plant malformation, and foliar striping were observed on rice plants in an experimental field of INERA at Banfora located in western Burkina Faso. Disease incidence in the field was estimated to be 80 ± 5%. The symptoms of disease were successfully transmitted to the susceptible rice (Oryza sativa) cultivar IR64 by soil transmission experiments (1). RSNV was detected by ELISA using a polyclonal antiserum (1), kindly provided by Dr. Denis Fargette, IRD, Montpellier, France. Total nucleic acid was extracted with TRIzol reagent (Invitrogen) from IR64 and field infected samples. The presence of the virus was confirmed by RT-PCR using primers 5'-CATCTTGTCGAGATGAG-3' and 5'-GCGTTGTCTTTATCAGTG-3' for specific sequences flanking the RNA2 CP gene. The RT-PCR product was directly sequenced and the sequence was deposited in GenBank (Accession No. LK023710). Sequence analysis showed that the CP gene of the RSNV isolate from Burkina Faso shared the highest nucleotide sequence identity (97.6%) with the known RSNV CP gene sequence from the Colombian isolate (EU099845) available in GenBank, confirming the presence of RSNV in the rice crops in Burkina Faso. To our knowledge, this is the first confirmed report of RSNV in Burkina Faso. Further studies are needed to determine its incidence and spread in the country. Detection of RSNV in Burkina Faso signals the urgent need for adoption of appropriate measures to restrict the spread and impact of this virus within Africa. References: (1) C. Fauquet and J. C. Thouvenel. Proc. Acad. Sci. Ser. D 296:575, 1983. (2) C. Fauquet et al. Develop. Appl. Biol. 2:71, 1988. (3) D. Louvel and J.-M. Bidaux. Agronomie Tropicale 32:257, 1977. (4) I. Lozano and F. Morales. Eur. J. Plant Pathol. 124:673, 2009.
RESUMO
Cowpea aphid borne mosaic virus (CABMV) diseased seeds provide at seedling, virus infected plants which are the only source of primary inoculum. Secondary infections are bequeathed by aphids. The objective of this research is to study the development of the secondary infection in field. Therefore, eight cowpea varieties with different seed contamination rate (0, 0.05, 0.25, 0.5, 1, 5%) were used over consecutive four years. The infected plants were recorded every week from the tenth day after sowing and over seven weeks. In the same way, aphids' population were evaluated in plots 30 days after sowing. There was no difference for the incidence rate between the average of plots sown with virus free-seeds and those sown with infected seeds with a rate of 0, 5%. In any case, the disease progressed lowly leading to incidences less than 50% at the post-flowering period in spite of a relatively high initial contamination rate of seed. For this group of varieties, the low progression of the disease indicated a high level of resistance to the infection. The high levels of infection especially observed with the varieties with high level of virus transmission to seed, translated the need to reduce aphids' population density notably by the use of insecticides during cowpea growing cycle. The high number of aphids and inoculum availability in the neighbouring plots were undoubtedly at the source of this result. This situation laid out the problematic of the use of seeds then little or not contaminated by the virus.
