First Occurrence of Calonectria Leaf Spot on Mexican Blue Palm in Italy

In April 2006, a new leaf disease occurred in a private garden in eastern Sicily (Italy) on young, 2-year-old seedlings of Mexican blue palm, Brahea armata S. Watson, in the Arecaceae. Symptoms were detected on 80% of seedlings. The leaves had minute, brown spots that enlarged into dark brown, circular or elliptical lesions, 3 to 6 mm in diameter, and with a necrotic, gray center. The lesions sometimes were surrounded by a chlorotic halo, and older leaves had larger chlorotic areas between spots. Conidia, conidiophores, and terminal vesicles were examined from diseased leaves. A Cylindrocladium sp. was consistently isolated from leaf lesions on Oxoid (Basingstoke, Hampshire, England) potato-dextrose agar after surface disinfestations with 0.8% NaOCl. Cylindrocladium isolates were cultured on carnation leaf agar (CLA) using single hyphal tips. Five isolates were established and identified as Calonectria pauciramosa C.L. Schoch & Crous based on obpyriform to broadly ellipsoidal terminal vesicles, conidiophore branching pattern, conidia size (52 × 4.6 μm), perithecium morphology, and ascopores size (36 × 6.8 μm). Perithecia were obtained with C. pauciramosa tester strains from Italy (G87 and G128) and South Africa (U 971 and U 1670) (2,3) that confirmed both mating types to be present. Further confirmation was obtained by internal transcribed spacer (ITS) analysis. The sequence of rDNA ITS1-5.8 S-ITS2 regions, obtained after amplification with primer ITS1 and ITS4, revealed that the Brahea isolates showed total homology with the sequence of the C. pauciramosa (STE-U 971 from soil) (= Cylindrocladium pauciramosum) available in GenBank. Isolate CBS 120619 from Mexican blue palm was deposited at Centraalbureau voor Schimmelcultures. Spray inoculations of 10 2-year-old Mexican blue palm seedlings were performed with a spore suspension of the fungus adjusted to 10⁵ conidia per ml obtained from 14-day-old single-spore colonies on CLA at 24°C under cool white fluorescent irradiation on a 12-h light/dark regimen. In addition, the following species were similarly inoculated using 10 1-year-old plants: Arecastrum romanzoffianum (Cham.) Becc., B. edulis H. Wendl. ex S. Watson, Chamaerops humilis L., Howea forsteriana Becc., Phoenix canariensis Hort. ex Chabaud., Trachycarpus fortunei (Hook.) H. Wendl., and Ravenea rivularis Jumelle & Perrier. Inoculated, and 10 control plants were placed in separate plastic bags in a growth chamber at 25 ± 1°C. After 7 to 10 days, foliar symptoms including flecks and spots developed on both species of Brahea and on Chamaerops humilis, and on these hosts, pathogenicity tests were repeated. Other palm species and control plants remained healthy. C. pauciramosa was consistently reisolated from inoculated plants on the basis of vesicle shape and conidia sizes of the anamorph. Cylindrocladium candelabrum, Cylindrocladium colhounii, Cylindrocladium floridanum, Cylindrocladium parasiticum, Cylindrocladium pteridis, Cylindrocladium scoparium, and Cylindrocladium theae have been reported as leaf spots pathogens of Arecaceae (1). To our knowledge, this is the first occurrence of C. pauciramosa on Mexican blue palm and the first report of the pathogen on Arecaceae. References: (1) P. W. Crous. Taxonomy and Pathology of Cylindrocladium (Calonectria) and Allied Genera. The American Phytopathological Society, St. Paul MN, 2002. (2) P. W. Crous et al. Stud. Mycol. 50:415, 2004. (3) G. Polizzi and P. W. Crous Eur. J. Plant Pathol. 105:407, 1999.