Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2005
Publication Date: 11/10/2005
Citation: Elliott, M.L., Rayamajhi, M.B. First report of Bipolaris sacchari causing leaf spot on Lygodium japonicum and L. microphyllum in Florida. Plant Disease. 89(11):1244. 2005. Interpretive Summary: Japanese and Old-world climbing ferns are two invasive weeds in Florida. During 2001, we isolated a fungus from diseased leaves of the Japanese climbing fern. The fungus was identified and evaluated for its disease-causing ability on both types of climbing ferns. Our results indicated that it caused disease on leaves of both types of ferns. This is the first report of the ability of this new fungus to cause disease on Japanese and Old-world climbing ferns in Florida. This new fungus will be further evaluated for its potential use as mycoherbicide on the Japanese and Old-world climbing ferns in Florida.
Technical Abstract: Lygodium japonicum (Japanese climbing fern) and L. microphyllum (Old world climbing fern) are invasive, noxious weeds in Florida. During 2001, L. japonicum sporelings collected from Hamilton, Highland and Madison Counties, and grown in shadehouse developed disease spots on pinnules (leaflets). A fungus with Bipolaris-like spores was isolated from affected pinnules, purified and stored for future evaluation. In early 2005, the fungus was grown on 1.5% water agar, with sterile wheat straw pieces embedded in the agar surface, at 26ºC with 12-h light. Conidia were 80.5 µm + 14.5 (range 53.2 to 123.4) x 15.1 µm + 1.6 (range 12.1 to 19.4) in size, pale brown, slightly curved, narrowly ellipsoid, without a protuberant hilum, distoseptate (8 + 1; range 6-10), with germination from both polar cells. Conidiophores were septate and smooth. Conidiogenous nodes were smooth. Based on these characteristics, the fungus was identified as Bipolaris sacchari. Pathogenicity toward both L. japonicum and L. microphyllum was determined using conidia produced on potato dextrose agar subjected to 12-h light at 26ºC. A 1 x 106 conidia ml-1 suspension was sprayed until runoff on healthy, small plants grown in containers. Control plants were sprayed with sterile water. There were four replicate plants per treatment. Plants were covered with plastic bags to maintain high humidity and placed in a growth chamber with a 12-h light and dark cycle, at 28ºC/~70% RH and 22ºC/~45% RH, respectively. Bags were removed after 72 h, and small (1-2 mm) water-soaked spots were evident throughout the plant canopy on both Lygodium species. Plants were incubated for three more weeks, under the same conditions, and then evaluated for disease. At least 50% of the L. microphyllum pinnules and 25% of the L. japonicum pinnules on each inoculated plant had either small brown leaf spots (1-2 mm) or larger necrotic spots (5 mm). Bipolaris sacchari was reisolated from spots; there was no evidence of fungal sporulation on the plants. No symptoms were apparent on control plants. To our knowledge, this is the first report of B. sacchari on a fern host in Florida.