Journal of Plant Pathology Archive

Abstract:

Algal spot symptoms appeared on Lansium parasiticum (Osbeck) Sahni & Bennet leaves in late August, 2014 when rainy and warm weather favoured algal growth. The disease was found in 20% of surveyed L. parasiticum plants in Songkhla, Thailand, showing an orange to brown small, 1-4 mm circular scurf on the leaves. Thalli were sub-cuticular with sub- epidermal growth, and consequent necrosis of epidermal cells in the leaf tissue. Filamentous algal cells were short and cylindrical, 8-15×3-7 μm, with length/width ratio 1:1.1-4. Setae were short filaments with two to five cells, 100-180 × 3-7 μm. Sporangiophores, on the upper leaf surface, developed from the thalli of the algal colony. Sporangia were elliptical, 5-10×5- 8 μm. Gametangia were spherical to elliptical (8-15×3-7 μm), produced beneath the cuticle. Gametes were spheroidal (7-10×7-9 μm), zoospores were elliptical (5-10×5-8 μm). These morphometric traits were consistent with Cephaleuros sp. (Thompson and Wujek, 1997). The sequence of the 18S rDNA (GenBank accession No. LC086008), showed 94% identity to C. virescens (KM020142) and C. parasiticus (KM020146). In pathogenicity test, leaves of healthy L. parasiticum were wounded by rubbing with celite, inoculated by spraying with a suspension of algal thallus fragments (0.1 g/ml fresh thalli w/v) (Suto and Ohtani, 2011). Algal infection was evident after three months when small thalli (0.2 - 0.6 cm diameter) were observed. Reisolated algae were consistent with those originally isolated. To our knowledge, this the first report of algal leaf spot of L. parasiticum caused by Cephaleuros sp.