COLLETOTRICHUM COCCODES: A SOIL-BORNE PATHOGEN DANGEROUS TO A PEPPER ROOTSTOCK IN ITALY

Abstract

During a survey carried out in July 2011 in Piedmont (north- ern Italy), root rots were repeatedly observed on grafted and non- grafted sweet pepper (Capsicum annuum) plants. Affected plants were stunted, had yellow leaves and a heavily damaged root sys- tem, exhibiting extensive necrosis of old and young roots, which were blackish and cracked. The cortex of necrotic roots could readily be removed, showing the heavily darkened internal tis- sues. Symptoms were particularly evident on older rootstock roots, whose tissues were grey to black. Disease incidence in the pepper rootstock cv. Rocal grown under plastic tunnel was about 35%. Colletotrichum coccodes (Bailey and Jeger, 1992) was re- peatedly and consistently isolated from infected tissues in potato dextrose agar. Hyaline, aseptate and thin- walled conidia (7.7- 18.9×3.2-5.3, average 11.4×4.3 μm size) were abundantly pro- duced in acervuli, and black round sclerotia (diameter 90×68 μm) were also observed. DNA was extracted from a pathogen isolate denoted CC1, using the Nucleospin Plant kit (Macherey Nagel, USA). The nuclear rDNA region (ITS) was amplified using the universal primers ITS1/ITS4 (White et al., 1990), the amplicon (451 bp) was custom-sequenced by LMU (Germany) and the se- quence deposited in GenBank (accession No. JQ290351). This sequence showed 99% homology with that of C. coccodes (AB233340.1). For pathogenicity tests (repeated twice) 15 healthy 20-day-old cv. Rocal plants were inoculated by dipping the roots in a fungal spore suspension (106 CFU/ml), whereas control plants were dipped in water. All plants were grown in a greenhouse at 22-25°C. Thirty days after transplanting, root rot symptoms were observed on all inoculated plants. C. coccodes was consistently reisolated from inoculated plants but not from the controls.