The replication of Citrus tristeza virus VT isolates in ornamental Citrus and related rutaceous species implicates them as potential virus reservoirs in the Mediterranean area

According to the pest surveillance guidelines on non-EU Citrus tristeza virus (CTV) isolates, a study was undertaken to evaluate the impact of the virus on ornamental and wild rutaceous species as well their potential role as reservoir of VT isolates. Budsticks of Severinia disticha, Fortunella margarita, F. obovata, Microcitrus papuana, Citrus micrantha var. microcarpa, C. hystrix, C. madurensis, C. aurantifolia and C. jambhiri grafted onto seedling rootstocks were bark patch inoculated in a greenhouse with a severe seedling yellows (SY) VT isolate and its homologous asymptomatic and cross protective variant. Except for S. disticha, all of them showed a high and variable replication rate of the virus, as confirmed by RT-real time PCR assays. C. micrantha var. microcarpa and F. margarita, grafted on sour orange, showed typical CTV symptoms when infected by the severe isolate. M. papuana showed leaf drop and stunting despite being grafted on volkameriana lemon rootstock. Additional tests were carried out on Troyer citrange and Poncirus trifoliata seedlings by bark patch inoculation of three severe SY-VT and three non-seedling yellows (non-SY) VT genotype isolates. All the severe isolates replicated at different level in citrange, whereas only one was shown to replicate in P. trifoliata, maybe due to insufficient growth. RT-real time PCR tests specific for detection of resistance breaking isolates were negative. The potential risks of aphid transmission by A. gossypii prevalent in the Mediterranean area is also discussed.