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

Abstract

In 2002 eggplant production in several glasshouses, polytunnels and fields was surveyed in the provinces of Adana and Mersin, southern Turkey. Some plants exhibited leaf chlorosis and slight vein clearing on outer leaflets, followed by yellowing and dropping of leaves, then vascular discoloration of the stem and finally death of the above-ground parts. 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 were investigated using PDA and carnation leaf agar (Nelson et al., 1983). All isolates obtained were identified as Fusarium 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. 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 Solanum melongena (eggplant cv. Pala) at the six-leaf stage. Wounded roots were submerged for 10 min in a conidial suspension (1 × 106 conidia mL−1 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 using a wilt index. All the isolates tested were pathogenic to eggplant. Symptoms observed on inoculated plants were similar to those in commercial glasshouses, including leaf chlorosis and necrosis; all inoculated plants died. Control plants showed no symptoms, and two other members of the Solanaceae (tomato and pepper) tested with the same method displayed no symptoms. Fusarium oxysporum f. sp. melongenae was successfully reisolated from the stems of disease-affected inoculated plants, thereby completing Koch's postulates. This is the first report of F. oxysporum f. sp. melongenae in Turkey. This study is dedicated to the memory of Assoc. Prof. Dr Yeter Canıhoş who passed away in 2002.