Unlocking factors, temporal trends, and management strategies for viral diseases in Cameroonian yams (Dioscorea spp.) germplasms

Viral disease poses a major threat to yams (Dioscorea spp.) cultivation in sub-Saharan Africa. Therefore, the aim of this study was to conduct a comprehensive analysis of incidence, climate impacts, role of vectors, and temporal trends of yam viral diseases (YVD), and it is crucial to set effective strategies for disease management and sustainable yam production. In this study, two successive field trials were conducted using 224 yam accessions, which were collected from the main yam-growing regions of Cameroon. Based on symptomatology, the viral disease incidence, severity, and temporal trends were evaluated for the yam germplasms, and they continued every two weeks and lasted for six months. Molecular validation of three principal yam-infecting viruses: yam mosaic virus (YMV), yam mild mosaic virus (YMMV), and cucumber mosaic virus (CMV) was confirmed by multiplex reverse transcription polymerase chain reaction (RT-PCR) technique. YMV and YMMV were detected in 42.6% and 6.3%, respectively, from the 789 leaf samples, whereas CMV and mixed infections were absent. The viral disease incidence was increased initially by 7.2% at four weeks after planting (WAP), to 30.2% at 16 WAP, and 30.5% at 20 WAP, followed by the intensity was declined. The area under the disease progress curve (AUDPC) was significantly higher in D. cayenensis (df=4.50, F=61.57, p≤0.001) compared to other species. The mealybugs (Planococcus citri) and scale insects (Stictococcus vayssierei) were detected as potential vectors, whereas the potyvirus vectors were absent. In consequence, principal viral pathogens, possible vectors, and temporal progression of YVD in yam species across the growing season were successfully mapped out. This study uncovers viral disease-causing factors, temporal trends, and management strategies of viral diseases of yams. Moreover, these findings set a new basis for disease surveillance and early diagnosis systems of viral diseases that open a way for sustainable yam cultivation in Cameroon, the entire central Africa, and the Congo Basin.