First report of Fusarium wilt of eggplant caused by Fusarium oxysporum f. sp. melongenae in Turkey

In 2002, eggplant production in several greenhouses, polytunnels and fields was surveyed in the provinces of Adana and Mersin; located at the south of Turkey. Some plants exhibited leaf chlorosis as slight vein clearing on outer leaflets, followed by yellowing and dropping of leaves (Fig. 1), then vascular discoloration of stem (Fig. 2) and finally death of the above ground parts (Fig. 3).

Isolations were made from the discoloured stem vascular tissue. Necrotic tissue fragments were surface-sterilized (2% NaOCl) and plated on potato dextrose agar (PDA). A Fusarium species was the only fungus isolated and appeared from most fragments. Single spore isolates were obtained and the culture characteristics and micromorphology investigated using PDA and carnation leaf agar (Nelson et al., 1983). All isolates obtained were identified as F. oxysporum due to production of characteristic three- to five-septate, sickle-shaped macroconidia, with a foot-shaped basal cell, ellipsoid microconidia borne in false heads on short monophialides, and chlamydospores in culture (Fig. 4). A typical cream-coloured colony developed on PDA, with purple pigmentation on the reverse side (Booth, 1971; Nelson et al., 1983). Fusarium wilt of eggplant is caused by Fusarium oxysporum f. sp. melongenae.

Pathogenicity tests were performed twice for each isolate using a root-dip inoculation method modified from Biles & Martyn (1989). In total, 74 Fusarium isolates were tested on seedlings of eggplant cv. Pala (Solanum melongena) at the six-leaf stage. Wounded roots were submerged for 10 min in a conidial suspension (1x10⁶ conidia per ml in sterile H2O), while control plants were dipped in sterile tap water. Seedlings were transplanted into pots and maintained in a growth chamber. After 3 weeks, severity of wilt symptoms was assessed on the leaves by a wilt index. All of the tested isolates were pathogenic to eggplant. Symptoms observed on inoculated plants were similar to those in commercial greenhouses, including leaf chlorosis and necrosis; all inoculated plants died. Control plants showed no symptoms and two other members of Solanaceae (tomato and pepper) tested with the same method displayed no symptoms. F. oxysporum f. sp. melongenae was successfully re-isolated from the stems of the inoculated plants, thereby completing Koch's postulates.

This is the first report of F. oxysporum f. sp. melongenae in Turkey.