First report of leaf spot on blue lupin (Lupinus pilosus) caused by Pleiochaeta setosa in Israel

Pleiochaeta setosa Kirchn. causes brown spot and root rot, serious diseases of lupin (Lupinus spp.) worldwide (Yang and Sweetingham 2002). Lupinus pilosus Murr., blue lupin, is a wild native species in the Mediterranean region but lately grown in private and public gardens as an ornamental plant. L. pilosus also has the potential to serve as a genetic source for breeding commercial lupin species due to its adaptation to calcareous soils, and high range of intraspecific variation (Brand et al. 2002). During February 2015, brown necrotic spots were observed on leaves and petiols of blue lupin in a 0.1-ha public garden in Ramat-Gan (central Israel). The disease affected about 90% from hundreds of plants. Symptoms included circular or irregular-shaped, dark brown, necrotic lesions not limited by leaf veins. Small pieces (1 to 2 mm) from infected leaves and petioles, were placed in 0.3% hypochlorite solution for 30 s, washed twice with sterilized water, and placed onto potato dextrose agar (PDA). Isolation yielded dark, olive-green colonies. Cultures were grown at 25°C with a 12-h photoperiod/day. Morphological examination of the mycelia and conidia in comparison with the literature (Garibaldi et al. 2012) indicated the fungus was P. setosa Kirchn. Mycelium had hyaline, septate hyphae that became dark olive on maturation and produced dark chlamydospores. The conidia were cylindrical with a truncated base, three to seven transverse septa and three to five hyaline appendages. Apical and basal cells were subhyaline, whereas the intermediate cells were olive-brown. The conidia measured 65 to 90 × 15 to 23 (average 76 × 19) μm. Appendage length was 40 to 130 (average 76) μm. DNA was extracted and the rDNA internal transcribed spacer region of three isolates was amplified using primers ITS1 and ITS4, and sequenced. BLAST analysis of our 517-bp fragments (represented by GenBank Accession No. KR536610) showed 100% identity to ITS rDNA sequences of P. setosa (EU167563 and JQ358708). Pathogenicity of two isolates (PSLP1 and PSLP2) was verified by two assays: (i) 5-mm-diameter PDA disks colonized by mycelium from 14-day-old cultures were placed onto five attached leaves of three healthy blue lupin plants (15 leaves in total). The plants were covered with plastic bags for 4 days in a growth chamber set at 23°C with a 12-h photoperiod/day. (ii) Five µl of an aqueous suspension of mycelium scraped from 14-day-old PDA cultures were placed on detached leaves, which were in turn placed on water agar in three petri dishes (three leaves per dish) and incubated at 25°C (12-h photoperiod/day) for 10 days. Three plants inoculated with noncolonized PDA disks and three detached leaves inoculated with sterilized water (treated as described above) served as negative controls. Lesions developed on the attached and detached leaves 4 and 10 days after inoculation, respectively, whereas control plants and detached leaves remained asymptomatic. P. setosa was isolated (as described above) consistently from these lesions. Similar pathogenicity tests with isolate PSLP1 were also carried out successfully on L. albus and L. palaestinus plants and leaves. P. setosa was reported on several lupin species (Yang and Sweetingham 2002). This is, to our knowledge, the first report of P. setosa on L. pilosus in Israel or anywhere in the world.