Abstract
In Japan, citrus greening is routinely diagnosed using PCR amplification of DNA fragments of the pathogenic bacterium ‘Candidatus Liberibacter asiaticus’ (Ca. Las). The temporal change in the distribution of PCR-positive tissue within a canopy of Citrus depressa was examined in five trees in Okinawa for 1 year, using the MHO 353/354 primer set. During spring and summer, Ca. Las was detected most frequently from samples collected in May by PCR. There was little difference in the frequency of detection of Ca. Las among petals, peduncles, the bark of twigs, and the midribs of leaves. The frequency of detection varied from one sub-main branch to another. Sub-main branches that showed a high frequency of detection maintained the trend throughout the year. The frequency of detection remained unchanged at low levels in some sub - main branches, whereas it increased later in other sub-main branches. There was little association between the frequency of detection within a sub-main branch and the degree of foliar symptoms on the branch. Based on these observations, the optimum sampling methods for detecting Ca. Las from a suspected tree by PCR, which includes pooling of several leaf samples for a single DNA extraction, is discussed.
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