Susceptibility of Prunus rootstocks to natural infection of Plum pox virus and effect of mineral oil treatments.

The use of rootstocks that are less susceptible or resistant to natural Plum pox virus (PPV) infection and/or the application of mineral oil treatments are two possible strategies to reduce viral incidence in nursery plots. We evaluated the susceptibility of Prunus rootstocks used in the Spanish stone fruit industry and the effect of mineral oil treatment (Sunspray Ultrafine at 1%) on the spread of the virus at two different localities in Valencia, Spain, under different natural PPV inoculum pressures (high inoculum pressure, 2006-08; low inoculum pressure, 2006-07). Samples from both plots were analysed by double-antibody sandwich indirect enzyme-linked immunosorbent assay (DASI-ELISA) and spot real-time RT-PCR. Under high inoculum pressure, the assayed rootstocks exhibited significant differences in their susceptibility to natural infection. The most susceptible rootstocks at the end of the experiment were Adesoto 101 and Mariana GF8-1. Cadaman and Garnem rootstocks presented the fewest PPV-infected plants; these infections could be detected only by spot real-time RT-PCR. No differences among the assayed rootstocks were found under low PPV inoculum pressure. Aphid species were monitored using Moericke yellow water traps and sticky-plant methods at both localities in May 2006 and 2007. Aphis spiraecola was the most abundant aphid species monitored by both methods at both localities. The average percentage of A. spiraecola carrying PPV PCR-amplifiable targets was 30.37% in the plot with high PPV inoculum pressure and only 7.98% in the plot with low inoculum pressure. We found significant differences in PPV incidence between Mariana GF8-1 plots that were treated with mineral oil and those that were not treated after one year under natural conditions and high PPV inoculum pressure. [ABSTRACT FROM AUTHOR]