RESUMEN
Bougainvillea (Bougainvillea spectabilis Willd) growing in 28 gardens during 2009 showed 100% disease incidence and 3 to 7% disease severity. Bougainvilleas with white flowers were the most affected. Symptoms consisted of light brown spots with dark brown margins visible on adaxial and abaxial sides of the leaves. Spots were circular, 2 to 7 mm in diameter, often surrounded by a chlorotic halo, and delimited by major leaf veins. Single-spore cultures were incubated at 24°C under near UV light for 7 days to obtain conidia. Pathogenicity was confirmed by spraying a conidial suspension (1 × 104 spores/ml) on leaves of potted bougainvillea plants (white, red, yellow, and purple flowers), incubating the plants in a dew chamber for 48 h and maintaining them in a greenhouse (20 to 24°C). Identical symptoms to those observed at the residential gardens appeared on inoculated plants after 45 to 60 days. The fungus was reisolated from inoculated plants that showed typical symptoms. No symptoms developed on control plants treated with sterile distilled water. The fungus produced distinct stromata that were dark brown, spherical to irregular, and 20 to 24 µm in diameter. Conidiophores were simple, born from the stromata, loose to dense fascicles, brown, straight to curved, not branched, zero to two septate, 14 × 2 µm, with two to four conspicuous and darkened scars. The conidia formed singly, were brown, broad, ellipsoid, obclavate, straight to curved with three to four septa, 40 × 4 µm, and finely verrucous with thick hilum at the end. Fungal DNA from the single-spore cultures was obtained using a commercial DNA Extraction Kit (Qiagen, Valencia, CA); ribosomal DNA was amplified with ITS5 and ITS4 primers and sequenced. The sequence was deposited at the National Center for Biotechnology Information Database (GenBank Accession Nos. HQ231216 and HQ231217). The symptoms (4), morphological characteristics (1,2,4), and pathogenicity test confirm the identity of the fungus as Passalora bougainvilleae (Muntañola) Castañeda & Braun (= Cercosporidium bougainvilleae Muntañola). This pathogen has been reported from Argentina, Brazil, Brunei, China, Cuba, El Salvador, India, Indonesia, Jamaica, Japan, Thailand, the United States, and Venezuela (3). To our knowledge, this is the first report of this disease on B. spectabilis Willd in Mexico. P. bougainvilleae may become an important disease of bougainvillea plants in tropical and subtropical areas of Mexico. References: (1) U. Braun and R. R. Castañeda. Cryptogam. Bot. 2/3:289, 1991. (2) M. B. Ellis. More Dematiaceous Hypomycetes. Commonwealth Mycological Institute, Kew, Surrey, UK, 1976. (3) C. Nakashima et al. Fungal Divers. 26:257, 2007. (4) K. L. Nechet and B. A. Halfeld-Vieira. Acta Amazonica 38:585, 2008.
RESUMEN
In late 2007, a new disease was found in commercial cutflower fields of bells-of-Ireland (Molucella laevis L.) in Texcoco, Mexico. Four plantings surveyed during this time had 100% incidence. A few spots on cutflowers make them unmarketable. Symptoms consisted of gray-green spots on leaves, calyxes, and stems, which turned brown with age. Spots were initially circular to oval, delimited by major leaf veins, and were visible on both adaxial and abaxial sides of the leaves. A Cercospora species was consistently associated with the spots. The fungus was isolated on V8 agar medium. Three single-spore cultures were obtained from isolation cultures. Cultures were incubated at 24°C under near-UV light for 7 days. Pathogenicity was confirmed by spraying a conidial suspension (1 × 104 condia/ml) on leaves of 16 potted M. laevis plants, incubating the plants in a dew chamber for 48 h, and maintaining them in a greenhouse (20 to 24°C). Identical symptoms to those observed in the field appeared on all inoculated plants after 2 weeks. No symptoms developed on control plants treated with autoclaved distilled water. The pathogenicity test was repeated twice with similar results. The fungus produced erumpent stromata, which were dark brown, spherical to irregular, 10 to 26 µm diameter, and giving rise to fascicles of five to nine divergent conidiophores, which were clear brown, paler near the subtruncate apex, straight to curved, not branched, rarely geniculate with two to four septa, and 57 × 3.4 µm. The conidia were formed singly, hyaline, acicular, base truncate, tip acute, straight to curved with 11 to 19 septa, and 172 × 3.5 µm. Fungal DNA from single-spore cultures was obtained with a commercial extraction kit (Qiagen, Hilden, Germany), amplified with ITS5 and ITS4 primers, and sequenced. The sequence, deposited at the National Center for Biotechnology Information Database (GenBank Accession No. EU564808), aligned almost perfectly (99% identity) to the bells-of-Ireland isolates from California (GenBank Accession Nos. AY156918 and AY156919) and New Zealand (Accession No. DQ233321). A 176-bp species-specific fragment was amplified with CercoCal-apii primers but not with CercoCal-beta or CercoCal-sp primers. These results, coupled with the morphological characteristics (1) and pathogenicity test, confirm the identity of the fungus as Cercospora apii sensu lato (including C. molucellae) (2,3,4). Although C. apii sensu lato has been reported on other hosts in Mexico (1,2), to our knowledge, this is the first report of this disease on M. laevis plants in this country. References: (1) C. Chupp. A Monograph of the Fungus Cercospora. Cornell University Press, Ithaca, NY, 1954. (2) P. W. Crous and U. Braun. CBS Biodiversity Series 1:1, 2003. (3) M. Groenewald et al. Phytopathology 95:951, 2005. (4) S. T Koike et al. Plant Dis. 87:203, 2003.
