Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/8/2004
Publication Date: 1/1/2005
Citation: Rayamajhi, M.B., Pemberton, R.W., Van, T.K., Pratt, P.D. First report of infection of Lygodium microphyllum by Puccinia lygodii, a potential biocontrol agent of an invasive fern in Florida. Plant Disease. 89(1):110. 2005. Interpretive Summary: Old-World climbing fern is one of the most invasive weeds found in Florida. It has invaded over 50,000 hectares of wetlands and is rapidly spreading in natural and urban areas of south Florida. It is important that we develop self-sustaining control methods for this fern that are environmentally and economically compatible with south Florida's environment. The search and evaluation of natural enemies of this fern in native and introduced geographical areas is currently in progress. We discovered a rust fungus disease on another closely related fern called Japanese climbing fern in north Florida. In this research, the disease causing ability of the rust fungus from Japanese climbing was tested on the Old-world climbing fern in south Florida. The rust fungus caused foliar disease on Old-world climbing fern. However, the symptoms (pustules) were of smaller dimensions. The potential use of this rust as a classical biocontrol agent of Old-world climbing fern will be further investigated.
Technical Abstract: Lygodium microphyllum (Old-World climbing fern) is one of the most invasive weeds in Florida. The search and evaluation of biocontrol agents for this fern is currently in progress. Puccinia lygodii, previously recorded on L. volubile and L. venustum in South America, attacks foliage and severely damages L. japonicum (Japanese climbing fern) vines in north and central Florida. Puccinia lygodii infecting L. japonicum which occurs mainly in north and central Florida may not have opportunity to interact with L. microphyllum, which occurs in south Florida. Herein, we used two inoculation methods to test the possible pathogenicity of P. lygodii on the new host, L. microphyllum. Method-I was designed to imitate semi-natural inoculation technique in which three containerized (0.45 L capacity) L. microphyllum test plants (15 to 30 cm tall sporelings) were intermixed among a group of containerized (5.0 L capacity) P. lygodii infected L. japonicum plants (source of inoculum) in a glasshouse. In Method-II, uredospores obtained from pustules on diseased L. japonicum foliage was adjusted to 1 x 10^6 uredospores/ml and then misted on three L. microphyllum sporelings (same size as in Method-I) until foliage were completely wet. Then the plants were monitored for 8 weeks to detect rust symptoms. Minute cinnamon flakes that developed into eruptive pustules were seen on the lower surface of the pinnules ca 42 after treatment initiation (in both methods). Each method was repeated two times. Dimensions [29.7 (+ 3.7) x 23.5 (+ 2.6) µm] and morphology of urediniospores from pustules on inoculated L. microphyllum were similar to those observed for P. lygodii on other host systems. The potential use of P. lygodii as a classical biocontrol agent of L. microphyllum in south Florida will be further investigated.