| Summary: | The Japanese plum (Prunus salicina) industry is economically important in
Spain and in other countries with Mediterranean climate. P. salicina was described
as a natural host of Plum pox virus (PPV) in Spain in 1984, where the ‘Red Beaut’
cultivar become an important source of inoculum and it spread the virus to
apricots and plums along the Spanish Mediterranean coast. The spatial and
temporal spread of PPV was monitored along a twelve year period in a collection
of 41 Japanese plum cultivars, planted in Luchente (Valencia) in 1990. PPV
incidence in 1991 was 11% and reached 95% after 13 years. The spread of the
virus followed a logistic model without aggregation of the new infected trees
around the previously infected ones. In May of 1992, 2002 and 2003 the numbers
of aphid species landing on mature Japanese plum trees were estimated by
counting the number of shoots (average of different cultivars: 752) and aphids
trapped on “sticky shoots”. The proportions of the different aphid species
captured were: Aphis spiraecola (43%), A. gossypii (18%), Hyalopterus pruni (6%),
Brachycaudus prunicola (6%), A. craccivora (3%) and Myzus persicae (2%), and
other species (22%). Vigorous Japanese plum cultivars were the most visited with
5,606 aphids landing in May/tree. An average of 667 PPV-viruliferous aphids
visited each vigorous Japanese plum tree in May. The percentage of detection of
viral RNA in the aphid species that landed was 11.9%. This high incidence of
viruliferous aphids is consistent with the high incidence and rapid spread of PPV
in Japanese plums in the region. A complete serological and molecular
characterisation of the PPV isolates spreading in P. salicina in Spain showed that
only PPV-D was present. Seven different serogroups and variability in the
nucleotide sequence of the NIb and CP genes were found among 21 PPV isolates
studied. Pre-inoculation of trees with a typical PPV-D isolate did not cross-protect
Japanese plums against the infection with PPV-M inoculated by grafting. The
sensitivity to PPV-D of 33 Japanese plum cultivars was evaluated. Unmarketable
fruits from infected trees reached as maximum as 15%, making possible economic
profit in heavily infected plantations.
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