Importance of cowpea mild mottle virus on soybean (Glycine max) in Benin and effect of planting date on soybean (G. max) virus level in northern Benin

Abstract To improve soybean production in Benin, knowledge of prevalent viral diseases is needed. For this purpose, surveys were conducted in 2011 and 2012 to assess the importance of cowpea mild mottle virus (CPMMV) in 8 districts of Benin on 1103 soybean samples analyzed by ELISA. Furthermore, a study was conducted to determine the influence of three planting dates on occurrence of viral diseases of soybean at the experimental farm of the Faculty of Agronomy of the University of Parakou from July to October in 2011 and 2012. For that, five soybean varieties were planted in a split-plot design with planting date as the main factor and variety as the secondary factor. The prevalence of viral diseases was evaluated on leaf samples with virus-like symptoms using 5 specific antibodies. The results of the survey showed that CPMMV was present in 175 of the 523 fields inspected in 2011 (33.4%) and in 180 of the 580 fields in 2012 (32.6%). The highest prevalences were recorded in N'dali (46.7%), Save (44.4%) and Perere (41.7%) in 2011. In 2012, similar levels of infection were observed in these areas. In the field trial, cucumber mosaic virus (CMV) was the most predominant virus at the three planting dates, with reduced incidence at the late planting date. The prevalence of bean yellow mosaic virus (BYMV) and cowpea aphid-borne mosaic virus (CABMV) were not significantly different between planting dates. CPMMV prevalence was significantly higher at the late planting (17.8% in 2011 and 18.6% in 2012) than at the early and normal planting. The alfalfa mosaic virus was not detected during the experiment. Moderately resistant soybean varieties differed in their reaction to the tested viruses, and varieties with moderate resistance to the single viruses were identified.