First report of Eutypa lata on red currant (Ribes rubrum) in Italy

In 2005, symptoms of a new disease were first reported on red currant (Ribes rubrum) cv. Junifer in Trentino (northern Italy). Symptoms included small chlorotic leaves, shoots with shortened internodes, wilted branches and stem cankers that started from pruning wounds and penetrated into the wood (Fig. 1). Cross-sections of infected branches showed wedge-shaped cankers (Fig. 2). During the growing season, 4- to 5-year-old branches wilted and entire plants were killed in seriously infected orchards. Perithecial stromata were found on infected pruning remains on the soil surface. To date, three infected orchards have been identified in Trentino. One orchard (7000 m²) was seriously damaged showing symptoms on 83% of plants, which caused a yield loss of 80%. In the other two orchards (1500 and 2000 m²) the disease was less severe and limited to 3% and 5% of the plants respectively. The disease started from individual plants randomly distributed in the orchards and developed in large patches in the most affected areas. The pathogen was isolated from small portions of necrotic woody tissue which were cultured on chloramphenicol malt extract agar (MEA) medium.

Two isolates from infected plants were identified using molecular analysis. The Eutypa lata isolate 101932 (Centraalbureau voor Schimmelcultures) was used as a reference strain. DNA was extracted following the CTAB method and amplified by PCR using two primer pairs (Lata 1/Lata 2-1 and Lata 1/Lata 2-2) designed on the E. lata ITS regions (Lecomte et al., 2000). The amplicons from the two field isolates were each the same size as that of the reference strain. The teleomorph phase of the pathogen was identified on the basis of asci and ascospore morphology.

Pathogenicity tests were performed by inoculating two-year-old potted plants (red currant cv. Junifer) with one of the identified E. lata isolates. Holes (5 mm diameter) were drilled into the main stems of the plants. Agar plugs with fresh mycelia were inserted into these holes and the wounds were then sealed with laboratory film (Sosnowski et al., 2005). Sixteen months after inoculation, the plants showed shoot and foliar symptoms similar to those observed in infected orchards, including cankers around the inoculation points. The pathogen was re-isolated from the margins of the cankers and re-identified as E. lata, using molecular analysis. No symptoms were observed on control plants inoculated with sterile MEA. E. lata was previously reported on red currant in the Netherlands, but that report did not provide evidence to prove Koch's postulates (Wenneker et al., 2002). To our knowledge, this is the first report of E. lata on red currant in Italy and the first time that Koch's postulates have been satisfied for this pathogen on this host.