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DUTCH ELM DISEASE IN ITALY: STATUS OF THE DISEASE AND AGGRESSIVENESS OF THE ISOLATES OF CERATOCYSTIS ULMI

L. MITTEMPERGHER
Rivista di Patologia Vegetale
Serie IV, Vol. 17, No. 3/4 (Luglio-Dicembre 1981), pp. 115-125
Stable URL: http://www.jstor.org/stable/42556808
Page Count: 11
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
DUTCH ELM DISEASE IN ITALY: STATUS OF THE DISEASE AND AGGRESSIVENESS OF THE ISOLATES OF CERATOCYSTIS ULMI
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Abstract

The status of Dutch elm disease in Italy was surveyed by questionnaire. In the summer of 1979 the disease had invaded the whole country but was sporadically present in some of the most northern and southern regions. Very high percentages of attack, often higher than 50, are found in northern regions. By culturally testing about 200 isolates coming from all over the country, the presence of the more aggressive strain of C. ulmi was found everywhere except in Calabria and Sardinia. This strain dominates the fungus population, except in the most southern regions where the less aggressive one takes the advantage. I do not have enough data to state if this situation is stable or in evolution. The classification in culture of the isolates for aggressiveness is complicated because of the presence of more aggressive isolates of Eurasian and American origin. The great majority of the isolates were classed by means of two characters, growth rate and synnemata production, on two cultural media, but for very few isolates which remain dubious some other cultural feature such as presence of aerial mycelium must be considered. By inoculating 11 isolates on 3 clones of Siberian elm a relationship between cultural features and aggressiveness was found and confirmation of the existence of two distinct levels of aggressiveness without intermediate passages was obtained. Con la collaborazione del Corpo Forestale dello Stato è stata fatta una indagine a mezzo scheda sulla situazione della grafiosi in Italia. Nell'estate 1979 la malattia aveva invaso tutto il paese con percentuali di attacco molto alte particolarmente nelle regioni settentrionali mentre era presente sporadicamente in Trentino e nelle estreme regioni meridionali. Da un test colturale eseguito su 200 isolati è risultata la presenza del ceppo più aggressivo di C. ulmi dall'Alto Adige alla Sicilia; esso domina la popolazione del patogeno tranne che nelle regioni più meridionali dove il ceppo meno aggressivo è più abbondante. Non ho pero dati sufficienti per dire se questa sia una situazione bilanciata e quindi stabile. La classificazione in coltura degli isolati per l'aggressività è complicata per la presenza nel ceppo aggressivo di isolati di origine « euroasiatica » ed « americana ». La maggioranza degli isolati fu classificata per mezzo di due caratteri, crescita della colonia e produzione di coremi, rilevati su due substrati, ma per pochi isolati che rimasero dubbi si dovette considerare anche la presenza di micelio aereo. Prove di inoculazione di 11 isolati su 3 cloni di olmo siberiano confermarono la classificazione in coltura e l'esistenza di due distinti livelli di aggressività senza passaggi intermedi.

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