Prevalence And Management Of Viral Diseases And Associated Vectors In Hot Pepper (Capsicum Spp.) Production In Rwanda

Abstract

Hot pepper (Capsicum spp.) is a source of income, employment and foreign exchange in Rwanda. However, production of the crop is constrained by diseases and pests, mainly viruses and their vectors. Reports on presence of viral diseases in Rwanda are available but there is limited information on the pathogens responsible and their management. This study was carried out to establish farmers’ perceptions and knowledge of viral diseases, to determine the prevalence of viruses associated with hot pepper, to screen hot pepper genotypes for reaction to viruses and aphids, and to evaluate the effect of companion crops on aphids and associated-viral diseases. To establish farmers’ perceptions and knowledge of viral diseases, a survey was carried out in major hot pepper growing areas from February to March 2018 covering low, mid and high-altitude agro-ecological zones (AEZs). A total of 101 randomly selected farmers were interviewed, and results revealed that pests and diseases were the main production constraints as indicated by 86.1% of the farmers. Awareness of viral diseases varied significantly (χ2 = 20.116; p <0.001) among farmers across the AEZs as well as their knowledge on causes and management of the viral diseases (χ2 = 26.896; p = 0.003). During the survey mentioned above, 225 symptomatic leaf samples of pepper were collected and analysed to detect six viruses using serology assay and reverse-transcription polymerase chain reaction (RT-PCR). Incidence of viruses transmitted by aphids {Cucumber mosaic virus (CMV), Potato virus Y (PVY), Pepper veinal mottle virus (PVMV)} did not differ significantly (χ2 =3.48; p = 0.176) across AEZs while for seed-borne viruses {Tobacco mosaic virus (TMV) and Pepper mild mottle virus (PMMoV)} it differed significantly (χ2 =6.526; p = 0.038). The CMV was the most prevalent identified in 48% of the samples. Single and mixed virus infections were present in 36 and 34.6% of the samples, respectively.

Sequence as well as phylogenetic analysis confirmed the identity of the Rwandan CMV, PVMV, TMV and PeVYV virus isolates. The reaction of 18 hot pepper genotypes (9 local accessions from Rwanda National Genbank, 5 introduced lines from World Vegetable Center and 4 commercial varieties from seed companies) to viral infection and aphid infestation in the field was evaluated in mid and low AEZs. Fourteen (14) of the best field performing genotypes were further assessed for their reaction to artificially inoculated CMV in the screenhouse. Incidence of viral diseases and severity varied significantly (p < 0.05) among genotypes in the field and screenhouse. Genotype 00767PPR, 0802PPR and PBC 462 were consistently resistant while genotype HP 0117, PP9852170 and PP99505197 were moderately resistant under field and screenhouse conditions. The population of aphids on the genotypes did not differ significantly (p > 0.05) in genotypes. The potential of companion crops to reduce aphids and associated viral diseases in hot pepper was evaluated for two seasons. The CMV, PVMV and PVY were the viruses detected in the plots while for aphid species, it was M. euphorbiae and A. gossypii. The border crops (maize, sorghum, sunflower), significantly reduced (p < 0.05) the incidence of viral diseases in hot pepper by 31.9, 46.5 and 54.8%, respectively compared to the control. Intercropping was also effective where reductions in virus incidence were 35.3, 41.2 and 51.6%, respectively. Aphids population was not (p > 0.05) affected by treatments both experiments. These findings enhance the existing knowledge of causal agents of hot pepper viral diseases and their distribution in Rwanda. Genotypes found to be resistant maybe useful for breeding programs and hot pepper growers. Farmers can adopt the utilization of sorghum, sunflower and maize as border or inter-crops to control the spread of non-persistently aphid-transmitted viruses within hot pepper fields. This study provides important information for designing of long-term strategies for management aphids and virus diseases.