Lampranthus sp. N.B. Brown (figmarigold) of the Aizoaceae family is used as groundcover in gardens. In October of 2008, severe outbreaks of a previously unknown rot were observed in a nursery located in Liguria, near Savona (northern Italy), on 35-day-old rooted cuttings grown in a peat substrate. Approximately 50% of rooted cuttings of red-flowered cultivars were affected. Lesions on collars and young stems were brown, water soaked, and soft. Plants eventually collapsed as roots rotted. Thin, aerial hyphae were visible on the surface of the stems and substrate. Later, a thick, light yellow, mycelial mat surrounded infected plants. Tissue fragments were excised from the margins of the lesions, dipped in a solution containing 1% sodium hypochlorite, and plated on potato dextrose agar and a medium selective for Oomycetes (4). Plates were incubated under constant fluorescent light at 23 ± 1°C for 4 to 5 days. Hyphae of five isolates grown on V8 medium were aseptate and 4.2 to 7.9 (average 6.2) μm wide. Sporangia consisted of complexes of swollen hyphal branches. Oogonia were globose, smooth, and 23.5 to 28.0 (average 25.9) μm in diameter. Antheridia were barrel shaped, intercalary, and diclinous. Oospores were globose and 19.4 to 23.6 (average 21.4) μm in diameter. The internal transcribed spacer (ITS) region of rDNA of a single isolate (DB24112008) was amplified with primers ITS4/ITS6 and sequenced. A BLAST analysis (1) in GenBank of the 1,074-bp segment showed a 100% homology with the sequence of Pythium aphanidermatum (Accession No. EU245039). The nucleotide sequence has been assigned the GenBank Accession No. FJ492745. Pathogenicity tests were performed twice on a red-flower cultivar of a Lampranthus sp. grown in 1-liter pots containing a peat moss substrate infested with wheat and hemp kernels colonized with one isolate of P. aphanidermatum at a rate of 20 g/liter. Ten plants were grown in infested media and 10 plants were grown in noninfested media. Greenhouse temperatures were 18 to 24°C. The first symptoms of stem and root rot developed 15 days later, while control plants remained healthy. P. aphanidermatum was consistently reisolated from the lesions. To our knowledge, this is the first report of P. aphanidermatum on a Lampranthus sp. in Italy. The disease has been reported in Japan (3) in 2008, while in the United States, a Pythium sp. was reported on L. aureus and L. glomeratus (2). Currently, the economic importance of Pythium rot on figmarigold in Italy is still limited.
References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) D. F. Farr et al. Fungi on Plants and Products in the United States. The American Phytopathological Society, St Paul, MN, 1989. (3) H. Kawarazachi et al. J. Gen. Plant Pathol. 74:94, 2008. (4) H. Masago et al. Phytopathology, 67, 425, 1977.