First report of Rhizoctonia solani on Diplotaxis tenuifolia in Italy

Recently, perennial wallrocket (Diplotaxis tenuifolia) has become a widespread crop in the Piana del Sele area, Campania, southern Italy. In 2001 wallrocket was cropped on about 500 ha under glass (Giorgini, 2001) and by 2003 the area under cultivation had increased further. In the past 3 years, the appearance of bare patches has occurred on a number of farms in the area. Typically, germination failures and damping-off of plantlets were observable at the centre of the patch, while plants at the border showed slower development, yellowing and early senescence of leaves. Necrotic lesions developing on one side of both crown and taproot were also evident.

Isolations from infected tissues carried out on 2% water agar (WA) yielded 27 multinucleate Rhizoctonia isolates from samples collected in 12 different locations. Pairings on WA were made with tester isolates belonging to anastomosis groups (AG) 1 through 11 of R. solani according to Carling et al. (1996). All the isolates anastomosed with high fusion frequency with tester isolates Rh-74 and RT32 belonging to AG-4. Pathogenicity was tested in plastic pots containing sterilised soil infested with 3 selected isolates. Most seedlings underwent damping-off in a few days, while the remaining showed more- or less-developed necrotic areas at the crown level. Uninoculated control plants were unaffected.

There are no previous reports of R. solani on perennial wallrocket. Although R. solani is a common pathogen on Brassicaceae, most reports in the literature refer to AG-2-1. On the other hand AG-4 is known as the most polyphagous anastomosis group and it is believed to be able to infect plantlets of any crop species at the soil line (Anderson, 1982). Therefore, the increasing incidence of Rhizoctonia on perennial wallrocket appears to be related to an obvious boost of its inoculum potential in the cultivated soil caused by the repeated cropping of this plant species and on the persistence in the soil of the crop residues after the final harvest.