Seven accessions (named C1 to C7) of Bambara groundnut landraces were used. Five of them were collected from farmers’ saved seeds in different locations and the two remaining were from the seed bank of the Institute of Environment and agricultural Research (INERA). Seed coats of accessions C1, C2, C5 and C7 were entirely creamy while the remaining accessions had two-colored seed coats. Most their seed coats were creamy but they also included black or brown stripes.

CPMoV isolate BE273 collected from cowpea [10] was used as source of inoculum. The virus was first propagated by mechanical inoculation of cowpea plants kept in insect-proof cages. Two weeks after inoculation, symptom-bearing leaves from infected plants were harvested. Leaf samples were ground at the ratio of 1/10 (w/v) in 0.01 M sodium phosphate buffer, pH 7.4. The resulting slurry was squeezed through cheese cloth and carborundum 600 mesh was added to the extract. This extract was subsequently applied to two-week-old Bambara groundnut plants by carefully rubbing the upper surface of the leaves.

The experiment took place during the 2016 and 2017 cropping seasons (June to October) at INERA, Kamboinsé Research Station (12˚28 N latitude, 1˚32 W longitude). The field layout was randomized completely block design with four blocks and seven plots per block. The field was deeply ploughed and NPK fertilizer (14-23-14) was applied at 100 kg/ha. Seeds were planted in 80 cm spaced rows with 20 cm spacing in a single row. Two weeks after sowing, emerged plants were mechanically inoculated in two blocks and plants in the two remaining blocks were kept uninoculated. Sprays of insecticide consisting of a mixture deltamethrine and dimethoate were done fortnightly to minimize insect colonization of the field. For weed control, manual weeding was performed as necessary.

Data were collected from the five inner plants of the seven plants on each line. They included the date of symptoms appearance, type of symptoms, size of the plants, number of flowers at 50% flowering stage, weight of pods and seeds yield.

CPMoV presence was diagnosed in plants using the double antibody sandwich format of the enzyme-linked immunosorbent assay method as described by [13] . Briefly, young trifoliate leaves collected using cloves and placed in plastic sampling bags. Collected samples were processed by grinding the leaves with mortar and pestle in sample extraction buffer. The extract was centrifuged for 10 min at 8000 ×g and the supernatants were used for virus detection. A positive control sample and two negative controls consisting of healthy leaf sample extracts and extraction buffer only, respectively, were included in the tests. All samples were tested in triplicates and the reaction results were recorded as optical densities (OD) measured at 405 nm using a METERTECH Σ960 automatic microplate reader. A sample was considered positive for virus detection if the corresponding OD_405nm values were greater than the detection limit (mean OD_405nm from healthy sample negative control plus three times the standard deviation).

Statistical analyzes of the data were carried out using the XLSTAT software, version 7.1, 2004 and the R software [14] . Means of the measured parameters were compared by analysis of variance (ANOVA) and post-hoc separation of the means was done according to the Newman Keuls test at 5% significance level.

The dates of onset of symptoms obtained after inoculation of CPMoV ranged from 4 to 8 days. At 8 days post-inoculation (dpi), all the inoculated plants were symptomatic. The symptoms varied according to Bambara groundnut accessions. They consisted mainly of mild or severe mosaic, leaf deformation and stunting of the plants (Figure 1). No symptoms developed in non-inoculated plants throughout the whole study.

All samples collected from inoculated plants at 14 dpi responded positively to the DAS ELISA test, confirming the presence of CPMoV in inoculated plants. OD_405nm values from inoculated plant samples ranged between 1.373 and 2.293 which were more than 10 to 18 times the detection threshold of 0.126. Therefore, no ambiguous reaction was recorded despite the discrepancies in the variation of OD_405nm values. The lowest values were recorded in C6 (OD_405nm = 1.373) and C7 (OD_405nm = 1.548), whereas more than 2 OD units were obtained from all other accessions. Samples from non-inoculated plants were also tested by ELISA at 15 days after flowering and were found negative.

The time to flower varied from 33 to 42 days with an average of 37 days after sowing. Non-inoculated plants tended to flower earlier than diseased plants but

statistical analyses did not reveal any significant difference. Data on the number of flowers produced by both control and diseased plants are summarized in Table 1. On average, control and inoculated plants produced 11.5 flowers and 6.9 flowers, respectively in 2016. In 2017, the average per plant number of flowers produced by control plants was 8.8 whereas diseased plants produced 5.3 flowers on average. Statistical analyses indicated significant effect of the disease on the number of flowers produced in 2011 (F = 17.7, P = 0.001) as well as in 2017 (F = 26.3, P = 0.0003).

The effect of the disease on the number of flowers produced varied according to bambara groundnut accessions. In both years, control plants carried higher numbers of flowers for accessions C1, C5 and C7. No significant difference was observed for accessions C3 and C4 in any of the two years. For accessions C2 and C6, differences in flower production were significant in only one year.

As summarized in Table 1, the average number of pods produced per plant was clearly affected by the diseased. Significant differences were found between inoculated and non-inoculated plants in both 2016 and 2017 (P < 0.001). Higher

C1-C7, bambara groundnut accessions; data with the same letter in the same parameter and the same line are not significantly different by the Student-Newman-Keuls test (P < 0.05).

production of pods was observed in healthy plants in 2017, regardless of the accessions. In 2016, differences in pod production were not significant in accessions C4, C5 and C6. Altogether, the number of pods in diseased plant was reduced by 20.5% - 82.0% and 25.0% - 75.9% in 2016 and 2017, respectively. Over the two years, reduction in the number of pods over the two years varied between 22.8% and 78.9%. Virus infection also resulted in a significant reduction of the average pod weight Reduction in pod weight reached 52.1% and 64.9% in C2 and C1, respectively, but was highest (81.1%) in C3.

In 2016, the average per plant seed yield differed significantly between inoculated and non-inoculated plants (F = 341.7, P < 0.001). There was also a significant accession effect (P = 0.0003) as well as disease x accession interaction (P = 0.0002). In average, healthy plants produced between 7.7 g/plant in accession C6 and 15.7 g/plant in accession C2 (Figure 2(a)). Altogether, healthy plants yielded 10.8 g of seeds per plant. Seed production in diseased plants was very low and varied from 1.3 to 4.4 g/plant in average (mean = 3.2 g). The lowest and highest yields were recorded in accessions C1 and C7, respectively.

Seed production in 2017 is illustrated in Figure 2(b). Similarly to 2016, seed production in 2017 was significantly affected by virus infection (P < 0.001). Accession effect was also significant (P = 0.0268) no effect of the interaction between disease presence and bambara groundnut accession was observed (P = 0.3445). In average, healthy plants produced 8.7 g of seeds per plant which clearly contrasted with the level of seed production in diseased plants (2.7 g/plant).

Altogether, bambara groundnut accessions incurred severe yield loss caused by virus infection (Table 2). The highest losses were recorded in accessions C3 (83.9%) and C1 (81.0%). Accessions C6 and C7 were the least affected with yield losses of around 50%.