Cylindrocarpon spp. have been described as producing root rot in Quercus spp. in forest nurseries, mostly when the host plants were weakened (1). To our knowledge, this is the first description of root rot of Mediterranean Quercus (Q. ilex, Q. suber, and Q. faginea) seedlings caused by C. destructans. In spring 2000, heavy mortality of Quercus seedlings was recorded in a nursery in southeastern Spain. The affected plants were 9 months old and growing in the open air in fertilized peat. Symptoms consisted of browning and wilting of leaves, with extensive necrosis of feeder roots. C. destructans (macroconidia averaging 36 × 6 μm, 1 to 3 septate; microconidia 10 × 3 μm; chlamydospores rough, single, or in chains, averaging 9 μm in diameter) was consistently isolated from the necrotic rootlets. Pathogenicity of one isolate from Q. faginea and of a mixture of isolates from the three affected Quercus spp. was determined. Fungal isolates were grown on potato dextrose agar plates for 1 month to allow chlamydospore production, and the inocula were prepared by mixing the contents of three colonized plates with 125 ml of sterile water. Six replicates of 12-month-old Q. ilex and Q. suber seedlings were inoculated by mixing the inoculum from the three plates with the potting medium prior to planting the seedling. All inoculated and control plants (only water added) were grown in a sand-lime-peat soil mixture under greenhouse conditions and watered as needed. After 5 weeks, all the inoculated plants showed extensive root necrosis accompanied by crown symptoms and rapid plant death. No symptoms were evident in control plants, and they produced new rootlets. No significant difference in pathogenicity was noted between the single isolate compared with the mixture of isolates, and the Quercus species did not significantly differ in susceptibility to root rot. C. destructans was easily recovered from necrotic roots.
Reference: (1) D. Brayford. Cylindrocarpon. Pages 103--106 In: Methods for Research on Soilborne Phytopathogenic Fungi. American Phytopathological Society, St. Paul, MN, 1992.
