Detection of Prunus necrotic ringspot virus in almond:: effect of sampling time on the efficiency of serological and biological indexing methodologies

The reliability of enzyme-linked immunosorbent assay (ELISA) and indexing methodologies for the detection of Prunus necrotic ringspot virus (PNRSV) in almond was assessed under local conditions. Thirteen field-grown almond trees were sampled fortnightly throughout the growing season. Petal and leaf homogenates were used for ELISA and to inoculate herbaceous indicator species, while buds collected from October onwards were budded to woody indicators. ELISA reliably detected PNRSV in petals and young leaves from bud-break until the cessation of stem elongation. While herbaceous indexing was not as reliable as ELISA, woody indicators could differentiate positive from negative samples reliably throughout the testing period. However, for mass screening of foundation plantings, nursery stock and elite germplasm, woody indexing is too costly and slow to give results. The use of ELISA can overcome these limitations but the timing of sample collection is critical. Petal or leaf tissue collected early in the season will yield the most reliable results.