First Report of Leaf Spot Caused by Phyllosticta yuccae on Yucca filamentosa in Brazil
Authors: Silva A. D. A. , Pinho D. B. , Junior B. T. Hora , Pereira O. L. 
Published: May 2013

Yucca filamentosa L. (Agavaceae), commonly known as Adam's needle, is known in Brazil as “agulha-de-adão.” It is an ornamental garden plant with medicinal properties (4). In 2010, 100% of Y. filamentosa seedlings and plants were observed with a severe leaf spot disease in two ornamental nurseries located in the municipality of Viçosa, Minas Gerais, Brazil. Initially, lesions were dark brown, elliptical, and scattered, and later became grayish at the center with a reddish brown margin, irregular and coalescent. Infected leaf samples were deposited in the herbarium at the Universidade Federal de Viçosa (Accession Nos. VIC32054 and VIC32055). A fungus was isolated from the leaf spots and single-spore pure cultures were obtained on potato dextrose agar (PDA). The sporulating single-spore cultures were deposited at the Coleção de Culturas de Fungos Fitopatogênicos “Prof. Maria Menezes” (CMM 1843 and CMM 1844). On the leaf, the fungus produced pycnidial conidiomata that were scattered or gregarious, usually epiphyllous, immersed, dark brown, unilocular, subglobose, and 95 to 158 × 108 to 175 μm, with a minute, subcircular ostiole. Conidiogenous cells were blastic, hyaline, conoidal, or short cylindrical. Conidia were aseptate, hyaline, smooth walled, coarsely granular, broadly ellipsoidal to subglobose or obovate, usually broadly rounded at both ends, occasionally truncate at the base or indented slightly at the apex, and 7.5 to 13.5 × 6 to 10 μm. Conidia were also surrounded by a slime layer, usually with a hyaline, flexuous, narrowly conoidal or cylindrical, mucilaginous apical appendage that was 10 to 16 μm long. Spermatia were hyaline, dumbbell shaped to cylindrical, both ends bluntly rounded, and 3 to 5 × 1 to 1.5 μm. These characteristics matched well with the description of Phyllosticta yuccae Bissett (1). To confirm this identification, DNA was extracted using a Wizard Genomic DNA Purification Kit and amplified using primers ITS1 and ITS4 (2) for the ITS region (GenBank Accession Nos. JX227945 and JX227946) and EF1-F and EF2-R (3) for the TEF-1α (JX227947 and JX227948). The sequencing was performed by Macrogen, South Korea. The ITS sequence matched sequence No. JN692541, P. yuccae, with 100% identity. To confirm Koch's postulates, four leaves of Y. filamentosa (five plants) were inoculated with 6-mm-diameter plugs from a 7-day-old culture growing on PDA. The leaves were covered with plastic sack and plants were maintained at 25°C. In a similar manner, fungus-free PDA plugs were placed on five control plants. Symptoms were consistently similar to those initially observed in the nurseries and all plants developed leaf spots by 15 days after inoculation. P. yuccae was successfully reisolated from the symptomatic tissue and control plants remained symptomless. P. yuccae has been previously reported in Canada, the Dominican Republic, Guatemala, Iran, and the United States of America. To our knowledge, this is the first report of P. yuccae causing disease in Y. filamentosa in Brazil and it may become a serious problem for the nurseries, due to the severity of the disease and the lack of chemical products to control this pathogen.

References: (1) J. Bissett. Can. J. Bot. 64:1720, 1986. (2) M. A. Innis et al. PCR Protocols: A guide to methods and applications. Academic Press, 1990. (3) Jacobs et al. Mycol. Res. 108:411, 2004. (4) H. Lorenzi and H. M. Souza. Plantas Ornamentais no Brasil. Instituto Plantarum, 2001.