Distribution of Ugandan Passiflora Virus (Potyvirus passiflorafricanse) in Major Passion Fruit Growing Areas in...

Passion fruit (Passiflora edulis Sims) is an important economic fruit crop in Rwanda grown for both domestic consumption and export markets. However, viral diseases pose a significant threat to passion fruit production. Among these, passion fruit woodiness disease (PWD) is the most destructive, causing yield losses of up to 100%. A survey was carried out to assess the distribution of Ugandan passiflora virus (UPV; Potyvirus passiflorafricanse) in major passion fruit growing areas. UPV is one of the major viruses known to cause PWD. The incidence of viral symptoms observed in the field did not differ significantly among districts, ranging from 81% in Rusizi to 100% in Rwamagana. However, mean symptom severity scores varied significantly between districts, with the highest severity recorded in Kayonza (3.1) and the lowest in Rulindo (1.9). Serological analysis detected potyviruses in 44% of the total samples (n = 216), including 43% of symptomatic (n = 144) and 47% of asymptomatic (n = 72) leaf samples collected from passion fruit fields. Further analysis using Reverse-Transcription Polymerase Chain Reaction (RT-PCR) detected UPV in 56% of symptomatic (n = 126) and 53% of asymptomatic (n = 60) samples, corresponding to 55% of the total samples tested (n = 186). The virus was present in all surveyed districts, with UPV infection prevalence of 89% in Rusizi, 75% in Rwamagana, 74% in Karongi, 59% in Nyamagabe, 44% in Nyaruguru, 38% in Kayonza, and 30% in both Gakenke and Rulindo. Fifteen partial coat-protein gene sequences for the Rwandan isolates were obtained. The newly described Rwandan isolates shared 97-99% nucleotide (nt) identity with one another, 89-94% with previously reported Rwandan isolates, 81-97% with Ugandan isolates, and 80-82% with Kenyan UPV isolates, suggesting that the Rwandan virus population is relatively homogenous. Genetic distances among the 15 new UPV isolates and previously reported Rwandan, Ugandan, and Kenyan isolates were very short (0.01-0.03), indicating high sequence similarity. All Rwandan isolates clustered into a single major clade, together with some Ugandan and Kenyan isolates. This close genetic relationship suggests a common ancestry and the regional spread of a single dominant UPV lineage. These findings highlight the need to reinforce seed and planting-material certification systems, as well as the need to enhance farmer capacity through targeted training on viral disease identification and management practices. This is vital to limiting the spread of viral diseases that threaten income security among smallholder passion fruit farmers.