Responses of Passiflora spp. to cowpea aphid-borne mosaic virus reveal infection in asymptomatic plants and new species with probable immunity

Passion fruit woodiness disease (PWD), caused by cowpea aphid-borne mosaic virus (CABMV), produces socioeconomic problems in Brazil. The objectives of this study were to i) evaluate the temporal progression of PWD, ii) identify Passiflora genotypes with resistance to CABMV, and iii) detect virus infection in asymptomatic plants by reverse transcription quantitative polymerase chain reaction (RT-qPCR) in cases where standard RT-PCR detection failed. The experiment was conducted in a greenhouse using 128 genotypes belonging to 12 species and three hybrids (inter- and intraspecific) of Passiflora, evaluated at five time points after inoculation. Progression rates and disease severity were lower in P. cincinnata, P. gibertii, P. miersii, and P. mucronata than in P. edulis, P. alata, Passiflora sp., and hybrids. Of the genotypes tested, 20.31% were resistant, especially the accessions of P. suberosa, P. malacophylla, P. setacea, P. pohlii, and P. bahiensis, which remained asymptomatic throughout the experiment. The absence of symptoms does not imply immunity of plants to the virus, since RT-qPCR analysis confirmed infection by the virus in asymptomatic plants of P. cincinnata, P. gibertii, P. miersii, P. mucronata, P. setacea, P. malacophylla, and P. suberosa. Even after four inoculations, the virus was not detected by RT-qPCR in the upper leaves in plants of the species P. pohlii and P. bahiensis, indicating that these species are probably immune to CABMV.