Selected mild strains of Passion fruit woodiness virus (PWV) fail to protect pre-immunized vines in Brazil

Abstract

The Passion fruit woodiness virus (PWV) is the most important virus affecting passion fruit (Passiflora edulis f. flavicarpa Deg.) crops in Brazil. The main purpose of this work was to select mild strains of PWV and to evaluate their protective effect against a severe strain of the virus. Three mild strains were selected from outstanding plants found in orchards severely affected by the virus (F-101, F-102 and F-103) and three others were obtained from blisters formed in passion fruit vine leaves showing mosaic (F-99, F-144 and F-145). The protective effect of the mild strains was evaluated for vines under greenhouse and field conditions. Plants pre-immunized with mild strains F-101, F-102 and F-144, in a greenhouse, had partial protection against the severe strain PWV-SP. In a first field experiment, all passion fruit vines pre-immunized with the six selected mild strains showed severe symptoms of the disease, approximately four months after the challenge inoculation with the PWV-SP strain. Results from a second field experiment, with vines preimmunized with strains F-101 and F-144, followed by a quantitative evaluation of the mild strains in different leaves of the protected plants, indicated that breakdown in protection seems to be related to the low concentration and/or irregular distribution of the mild strains in leaves, which allows the existence of infection sites available for the establishment of the severe strain. Pre-immunization was not an appropriate alternative for the control of the passion fruit woodiness disease.

Effect of Agaricus brasiliensis and Lentinula edodes mushrooms on the infection of passionflower with Cowpea aphid-borne mosaic virus

“…The evaluation of the protection was accomplished by the visual observation of plants exhibiting typical virus symptoms (mosaic, leaf deformation and leaf blisters) and by determining the disease´s incidence (test plants with symptoms/total) in each treatment 30 and 60 days after the inoculation. When necessary, the indirect DAS-ELISA test was carried out, as described previously (Bertacini et al, 1998;Novaes and Rezende, 2003) to prove that the symptomless plants were not infected by CABMV. The treatments that received mushroom extracts were compared individually with the control by Independence χ 2 test (P<0.05).…”

“…As a semi-perennial culture, established in the field for a few years, the crossprotection of the passion fruit plants could contribute to the reduction of the damages caused by the virus. However, so far, this action has not been effective in Brazil (Novaes and Rezende, 2003). Thus, other control measures should be found in an attempt to reduce the virus damage.…”

Detection of a resistance gradient to Passion fruit woodiness virus and selection of ‘yellow’ passion fruit plants under field conditions

“…Pre-immunization strategies, as used in Australia by Simmonds (1959), did not protect passion fruit plants in Brazil against CABMV (Novaes and Rezende, 2003). Currently, tests are being made with transformed plants resistant to CABMV (Alfenas et al, 2005;Trevisan, 2005).…”

Transformação genética de maracujazeiro azedo para resistência ao vírus do endurecimento dos frutos (Cowpea aphid-borne mosaic virus - CABMV)

“…O plantio de novos pomares próximos a pomares abandonados ou antigos, que podem servir como fonte de inóculo, e a dificuldade de controle dos vetores, podem ser considerados os fatores principais para a disseminação da doença. Além disso, nenhuma fonte de resistência ou tolerância à infecção pelo vírus tem sido encontrada no germoplasma de maracujá azedo cultivado e a pré-imunização, com isolados do PWV, não proporcionou proteção contra estirpes mais virulentas REZENDE, 2003). Uma alternativa para a eliminação do CABMV em maracujazeiro é a utilização da microenxertia a partir ápices caulinares de plantas infectadas, enxertados em epicótilo e hipocótilo de plantas sadias.…”