First Report of Fusarium Wilt Disease of Mimosa in Greece.

Mimosa, Albizia julibrissin, is an ornamental tree that thrives in Greece under difficult urban environmental conditions and is prized for its ability to create alleys. In 1991, at Kalamaria municipality, Thessaloniki, mimosa trees were found with symptoms of a Fusarium wilt disease and many trees were already dying or dead. The first symptom was a characteristic yellowing and wilting of foliage. Leaves on symptomatic trees fell prematurely and eventually the defoliated portion of crowns died. Numerous adventitious branches on the stems also developed wilt symptoms and died. When stems were cross-sectioned, a brownish discoloration in the spring wood vessels of the outer annual ring could be observed. In the more advanced stages of the disease, dark sap exudations flowed out of bark cracks. Orange-pink sporodochia with masses of conidia developed in bark cracks and lenticels. Of 1,520 trees examined for external symptoms in the autumn of 1991, 1,339 (88.2%) were apparently healthy, 96 (6.3%) had symptoms, and 85 (5.6%) were dead. In autumn 1992, the same trees were examined and the respective values were 1,276 (83.9%), 130 (8.6%), and 114 (7.5%). Wood samples from the most recent annual ring taken from 30 infected and 30 apparently healthy trees were plated on potato dextrose agar. Fusarium oxysporum was recovered from 93% of the symptomatic trees and only 7% of the asymptomatic ones. Since 1992, the disease has spread within the area where it was first found but has not been observed anywhere else in Greece. A disease of mimosa with similar symptoms was first reported by Hepting (1) in 1936 from North Carolina. The associated fungus Fusarium oxysporum f. sp. perniciosum was described by Hepting (2), who also demonstrated its pathogenicity. The disease has also been previously reported in Russia. This is the first report of mimosa wilt disease in Europe. References: (1) G. H. Hepting. Plant Dis. Rep. 20:177, 1936. (2) G. H. Hepting. USDA Circ. 535, 1939.