Since 1986, irregular, blotchy lesions of leaves and petioles of tulip tree (Liriodendron tulipifera L.) have been observed each summer in the city of La Plata, Argentina. Leaf spots are initially 2 to 3 mm in diameter and water soaked, and then they become brown or black with faint chlorotic margins that are more noticeable on the adaxial surface. Lesions may attain a diameter of 12 mm. Veins and petioles may also be affected and lesions may coalesce, especially at leaf margins. Surface-sterilized pieces of necrotic tissue collected from eight sites in the La Plata area were plated on potato dextrose agar and incubated at 27°C. Two Colletotrichum species were consistently isolated from the lesions. Single-spore cultures were obtained and identified as C. acutatum (1) and C. gloeosporioides (4). When cultured on V8 medium, mycelial growth of C. acutatum was tufted and pale gray, and the reverse side of colonies was buff to cream or pale gray to tan, but never dark. Hyaline conidia were buff to rosy buff en masse and elliptical or elongated with abruptly tapering ends measuring 8.04 to 13.58 × 2.68 to 3 μm. Micromorphology of conidia were compared with C. acutatum “Herb IMI 232176” (1). C. gloeosporioides cultures were dark gray; their reverse was dark mouse gray to fuscous black. The cirrhus was peach to orange and hyaline conidia were oblong with rounded ends measuring 8.6 to 13.40 × 2.68 to 4.02 μm. Pathogenicity was verified on greenhouse-grown tulip trees and strawberry cv. Pájaro (Fragaria × ananassa) by spray inoculation with conidial suspensions of C. acutatum (107/ml), C. gloeosporioides (106/ml), and a mixture of both species (equal parts of each suspension). Controls were sprayed with sterile distilled water. Irregular, blotchy lesions of tulip tree appeared 30 days after inoculation. Anthracnose symptoms (3) were observed on strawberries 7 days after inoculation. In all cases, lesions produced by the mixture were larger than those obtained with individual species. The inoculated fungi were reisolated from lesions of all species tested, fulfilling Koch's postulates. No lesions were observed on control plants. Voucher specimens were deposited in La Plata Spegazzini Herbarium, Argentina as C. acutatum (LPS 47187) and C. gloeosporioides (LPS 47188); cultures of both fungi were also deposited as LPSC 795 and LPSC 796, respectively. C. acutatum and C. gloeosporioides cause Liriodendron leaf blotch in Argentina. Glomerella cingulata was previously reported affecting L. tulipifera (2), but to our knowledge, this is the first report of tulip tree as a host of C. acutatum.
References: (1) B. J. Dyko and J. E. M. Mordue. No. 630 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1979 (2) K. Ito and T. Kobayashi. Bull. For. Exp. Stn. Meguro 146:1, 1962. (3) C. J. Ramallo et al. Plant Dis. 84:706, 2000. (4) J. A. von Arx. Phytopathol. Z. 29:413, 1957.