Genetic transformation of sweet passion fruit (Passiflora alata) and reactions of the transgenic plants to Cowpea aphid borne mosaic virus

Passion fruit woodiness disease, which is caused by the potyvirus Cowpea aphid borne mosaic virus (CABMV), is the primary constraint for passion fruit production in Brazil. Transgenic Passiflora alata lines that contain a CABMV-derived coat protein gene fragment in a hairpin configuration were obtained via Agrobacterium tumefaciens-mediated transformation. The plants were propagated and the reaction to CABMV infection was evaluated after three mechanical and one viruliferous vector inoculations. After three mechanical inoculations, two lines from a total of 21 transgenic lines tested maintained all four propagated clones symptomless. After the fourth inoculation, all transgenic lines presented at least one propagated clone infected with CABMV. However, 20 propagated clones from different transgenic lines remained asymptomatic. These asymptomatic plants were analyzed by RT-PCR and CABMV was detected in 17 plants. The estimated viral titers in these plants, which were determined by RT-qPCR, were consistently low compared with those of the positive control (non-transgenic inoculated plants). A biological virus recovery test was performed using leaf extracts from the three RT-PCR negative propagated clones and the absence of the CABMV was confirmed. The results of the present study indicate that the incorporation of CABMV-gene fragments into the Passiflora genome may influence the resistance of these plants to the pathogen.