Accurate diagnosis is a prerequisite to effective management of plant diseases especially those whose symptoms are not very specific. A survey was conducted from February to March 2018 to detect the presence and determine the distribution of six viruses infecting pepper in Rwanda. A total of 225 symptomatic samples were collected from high, mid and low-altitude zones, and analysed using serology assay with antibodies to cucumber mosaic virus (CMV), potato virus Y (PVY), pepper veinal mottle virus (PVMV), pepper mild mottle virus (PMMoV) and tobacco mosaic virus (TMV). Polymerase chain reaction was used to confirm the results from serology and to test for the presence of pepper vein yellows virus (PeVYV), which has no commercial antibodies. Amplified DNA fragments were sequenced and compared with other known pepper viruses available in the GenBank database. Seventy-three percent of the samples tested positive for at least one of the viruses. CMV, PVY, PVMV, TMV and PMMoV were detected in all zones but PeVYV was detected in the mid and low-altitude areas. CMV was the most widespread and was detected in 48% of the samples, followed by PVMV and PVY in 23.6% and 18.2%, respectively. There were both single (36%) and mixed (34.6%) infections of the viruses. Sequence and phylogenetic analysis confirmed the presence of CMV, PeVYV, PVMV and TMV in the country. This is the first report of TMV, PMMoV and PVY infecting pepper in Rwanda. Efforts towards the development of sustainable management for these viruses should be put in place to improve yields and quality of hot pepper.

Detection and distribution of viruses infecting hot pepper (Capsicum spp.) in Rwanda

Potato virus Y isolates infecting bell pepper from parts of Southern Africa display distinct recombination patterns

Chilli is infected by at least 65 viruses globally, with a mixed infection of multiple viruses leading to severe losses being a common occurrence. A simple diagnostic procedure that can identify multiple viruses at once is required to track their spread, initiate management measures and manage them using virus-free planting supplies. The present study, for the first time, reports a simplified and robust multiplex PCR (mPCR) assay for the simultaneous detection of five RNA viruses, capsicum chlorosis orthotospovirus (CaCV), chilli veinal mottle virus (ChiVMV), large cardamom chirke virus (LCCV), cucumber mosaic virus (CMV), and pepper mild mottle virus (PMMoV), and a DNA virus, chilli leaf curl virus (ChiLCV) infecting chilli. The developed mPCR employed six pairs of primer from the conserved coat protein (CP) region of the respective viruses. Different parameters viz., primer concentration (150–450 nM) and annealing temperature (50 °C), were optimized in order to achieve specific and sensitive amplification of the target viruses in a single reaction tube. The detection limit of the mPCR assay was 5.00 pg/µL to simultaneously detect all the target viruses in a single reaction, indicating a sufficient sensitivity of the developed assay. The developed assay showed high specificity and showed no cross-amplification. The multiplex PCR assay was validated using field samples collected across Northeast India. Interestingly, out of 61 samples collected across the northeastern states, only 22 samples (36%) were positive for single virus infection while 33 samples (54%) were positive for three or more viruses tested in mPCR, showing the widespread occurrence of mixed infection under field conditions. To the best of our knowledge, this is the first report on the development and field validation of the mPCR assay for six chilli viruses and will have application in routine virus indexing and virus management.

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A Simplified Multiplex PCR Assay for Simultaneous Detection of Six Viruses Infecting Diverse Chilli Species in India and Its Application in Field Diagnosis

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Current and Emerging Pests and Diseases of Cucumber ( Cucumis sativus L.) in Africa

Increasing outbreaks of virus species infecting pepper (Capsicum spp.) is a major problem for growers in Africa due to a combination of factors, including expansion of pepper cultivation, abundance of insect vectors and climate change. More than 45 viruses have been identified to infect pepper crops causing economic loss in terms of reduced quality and marketable yield, sometimes up to 100%. The Pepper veinal mottle virus (PVMV), Potato virus Y (PVY) and Cucumber mosaic virus (CMV) are endemic in many countries including Uganda, Mali, Cameroon, Morocco and Nigeria. Current management options for virus infection in Capsicum spp. is by the integration of several approaches. More importantly, eradication of infected plants, cultivation of disease resistant varieties, improved cultural practices and judicious use of insecticides especially when plants are young and easily colonized by vectors. In recent years, eco-friendly control measures are needful to reduce occurrence of virus diseases in Capsicum spp.

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Titilayo Ajose

Papers

Management of Viruses and Viral Diseases of Pepper ( Capsicum spp.) in Africa

Current and Emerging Pests and Diseases of Cucumber ( Cucumis sativus L.) in Africa