A survey of fungal diseases associated with Vitis

Abstract

A survey was carried out between July and September 2000 in 10 vineyards, 8 in Malta and 2 in Gozo to investigate fungal diseases of vines. Malta was divided into 2 sectors according to a map issued by the Works Department. Six samples were taken in sector 1 which represents central Malta, where the vineyards density is highest. The other two samples were from sector 2, representing southern Malta. Two other samples were taken from Gozo, represented by sector 3. Moreover samples were taken both from vineyards where traditional practices are used and vineyards where modern practices are employed. Field samples i.e. leaves, berries or sterns infected by the fungi were immediately transferred to the Plant Health Laboratory at Marsa and stored in an insulated container so as not to kill any fungi. At the laboratory, the samples together with the instruments and working bench were sterilised with appropriate disinfecting solutions. Infected plant organs were first carefully examined under a stereornicroscope for the presence of any fruiting bodies and fungal hyphae, and thereafter sectioned and cultured to grow the fungus found inside the plant tissue section. Culture media such as water agar, potato dextrose agar and Czapek dox were used according to whether a general or specialised culture medium was needed. Culture media were prepared in the preparation room and sterilised by an autoclave. They were then left to cool slightly to a temperature of 45° C. The prepared agar suspension was carefully poured in petri dishes in equivalent quantities to a depth of 5 mm. They were left to solidify in a laminar flow cupboard and annotated appropriately. Infected plant tissues were thereafter placed on the agar and after some days the fungi were examined under hoth a stereomicroscope and a high power microscope. Fungal characteristics were noted and were compared with characteristics in fungal keys and when matching was completed the fungi were identified. The study identified 26 different fungi and 21 genera of which 22 fungi were found for the first time in the Maltese Islands. The percentage composition of the examined fungi was as follows: 10% obligate parasites, 29% facultative parasites and 61 % saprophytes. The most common obligate fungi were powdery mildew and downy mildew. Some of the more important famultative fungi that were found in this July include Altemw ia, Botrytis and Stemphylium. Saprophytes included Aspergillus, Acremonium and Stachobotrytis amongst others. At the end of the project a comparison of the traditional and modern vine cultivation practices was discussed. It was observed that traditional varieties like Girghentina and Gellewza were found in the fields of individual or part-time fanners whereas international varieties were found in the vineyards of large wineries. Moreover the intensity of diseases was much more pronounced in the traditional rather than in the modern way of trailing the vine. Finally a risk assessment of the potential fungal diseases for Malta was made. Diseases such as Phomopsis viticola, Botryosphaeria dothidea, Elsinoe ampelina and Pseudopezicula tracheiphila were identified as the diseases that pose great risk for Malta. It was concluded that the Plant Quarantine Section should be upgraded and its structures reinforced to prevent the entry of the above mentioned diseases.