First Report of Leaf Spot of Garden Lupin (Lupinus polyphyllus) Caused by Pleiochaeta setosa in Italy

Lupinus polyphyllus Lindl., common name garden lupin, is used in commercial, private, and public landscapes and sold as a cut flower. During summer 2011, extensive brown necrotic areas were observed on young and old leaves of plants grown in a private garden near Biella (northern Italy). The disease affected about 50 of 80 2-year-old plants. Early symptoms included circular to irregular-shaped brown lesions of alternating pale and dark brown concentric bands. Lesions coalesced and often were surrounded by chlorotic halos at an advanced development stage. Lesion expansion was not limited by leaf veins. When lesions covered much of the leaf area, the leaf curled and remained attached. However, expansion of stem lesions often resulted in plant death. A fungus was consistently isolated from 15 infected leaves on potato dextrose agar (PDA). Cultures were grown at 21 to 25°C under 16 h of light and 8 h of darkness. Mature colonies were dark olive-green and produced orangeochre pigments in the medium. Ten isolates were obtained and three strains were used in the morphological study. The mycelium had olivaceous, septate hyphae that produced abundant dark, intercalary chlamydospores. The conidia were cylindrical to elliptical, slightly curved, with a truncated base, five to seven transverse septa and three hyaline appendages. Apical and basal cells were subhyaline, whereas the intermediate cells were olivebrown. The conidia measured 76 to 94 × 14 to 19 (average 85 × 16) μm. Appendages were up to 84 μm long. On the basis of its morphological characteristics the pathogen was identified as Pleiochaeta setosa Kirchn. DNA was extracted using Terra PCR Direct Polymerase Mix (Clontech). The internal transcribed spacer region of rDNA was amplified using primers ITS 1 and 4 (4) and sequenced. BLAST analysis (1) of the 570 bp fragment showed a 100% homology with a P. setosa isolate submitted to GenBank (accession no. EU167563). The nucleotide sequence was submitted to GenBank (JQ358708). Pathogenicity was verified on healthy 5-month-old garden lupin plants by placing 8-mm mycelial disks from 15-day-old cultures on 10 unwounded leaves per plant with five plants per treatment. Ten leaves of five plants were inoculated with PDA disks to serve as a negative control. Plants were covered with plastic bags for 4 days after inoculation and maintained in a growth chamber at 20 ± 1°C. Lesions developed on 80% of leaves 3 days after inoculation, whereas control plants remained healthy. P. setosa was consistently isolated from these lesions. The pathogenicity test was carried out twice. The presence of P. setosa on L. polyphyllus was reported in Australia, United States (2), and Poland (3). This is, to our knowledge, the first report of P. setosa in Italy. The impact of this disease is currently limited.References: (1) S. F. Altschul et al. Nucleic Acids Res., 25:3389, 1997. (2) A. M. French. California Plant Disease Host Index. Calif. Dept. Food Agric. Sacramento, 1989. (3) W. Mulenko et al. A Preliminary Checklist of Mycromycetes in Poland Polish Academy of Sciences, 1982. (4) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, 1990.