First Report of Cylindrocarpon destructans on English Walnut in Italy. L. Montecchio, Istituto di Patologia Vegetale, Universita degli Studi di Padova, v. Gradenigo, 6, I-35131 Padova. R. Causin, Istituto di Patologia Vegetale, Universita degli Studi di Padova, v. Gradenigo, 6, I-35131 Padova. Plant Dis. 79:967, . Accepted for publication 18 July 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-0967B.
In a nursery in northern Italy, rapid die-back developed on 2-year-old English walnut (Juglans regia L.) trees grown in containers of compost (sewage sludge, poplar bark, peat 1:2:5 vol/vol/vol). The foliage became slightly chlorotic, then quickly wilted and dried without leaf drop. Symptoms began on the outer leaves, but eventually all the foliage was affected. No apparent symptoms developed on branches, trunk, or collar, but widespread necrosis developed on the roots. Microscopic examination of infected root sections showed vessels frequently contained mycelium and tyloses that, in some cases, caused complete occlusion. Fungi were isolated from the internal tissues of infected roots onto potato-dextrose agar (PDA). Pure cultures of 14 isolates belonging to six different fungal genera, grown on PDA at 23 plus or minus 20C for 7 days in the dark, were inoculated individually into roots of healthy, 2-year-old trees. Inoculated trees were maintained in the greenhouse (21 p;us or minus 20C, 80% relative humidity 12 h per day of natural light) for 90 days. Symptoms equivalent to those on the nursery stock developed only on trees inoculated with three isolates of Cylindrocarpon destructans (Zinssmeister) Scholten. The pathogen was reisolated only from the trees with characteristic symptoms. The entire test was repeated in two successive years. The disease may become important in orchards and in breeding programs where susceptible English walnut is utilized as parental germ plasm.