Systemic infection of cowpea aphid-borne mosaic virus in Passiflora spp. occurs at the initial stage regardless of the species' resistance

Abstract

Passion fruit woodiness disease (PWD), caused by cowpea aphid-borne mosaic virus (CABMV), severely damages leaves and fruits, compromising passion fruit production. The dynamics of this infection in Passiflora spp. are still poorly understood. The objective of this study was to determine the systemic infection time of CABMV in Passiflora spp. and to quantify the viral titer throughout the infection. Plants of Passiflora edulis Sims. (BGP418, susceptible), P. cincinnata Mast. (BGP243, moderately resistant), P. setacea DC. (BRS Pérola do Cerrado, resistant), and P. suberosa L. (BGP152, resistant) were used. The study was conducted in a climate chamber, and mechanical inoculations were carried out on the first pair of basal leaves of the seedlings. Symptoms were assessed using a scale whose scores were converted into a disease index (DI%), and the viral titer was determined at different time points by real-time quantitative RT-PCR (RT-qPCR). The first symptoms of the virus were observed at seven days after inoculation (Dai) in P. edulis (DI = 5.15%) and at 10 Dai in P. cincinnata (DI = 8.86%). On the other hand, P. setacea and P. suberosa did not show typical symptoms of the disease (DI = 0.00%). Systemic CABMV infection was detected at 30 minutes after inoculation regardless of the level of resistance of the Passiflora species. There was an increase in viral titer with infection time with P. edulis and P. cincinnata, although in the case of P. edulis, the increase in CABMV titer occurred earlier, at 2 Dai, and in P. cincinnata at 8 Dai. In the asymptomatic species (P. setacea and P. suberosa), there was no variation in the viral titer over the time periods evaluated. This pioneering study provides information for the selection of time intervals for future molecular research into the interaction between Passiflora spp. and CABMV.