Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/9/2006
Publication Date: 8/1/2006
Citation: Widmer, T., Kirk, A., Kirk, G., Guermache, F. 2006. Foliar and cane rot of Arundo donax caused by Nigrospora oryzae in Europe. Plant Disease 90:1107 Interpretive Summary: Giant reed is a noxious weed that has invaded the United States from the Mediterranean region. It is a serious pest of riparian areas degrading habitats that support native plants important to wildlife. Traditional mechanical and chemical control and restoration methods are prohibitively expensive and can cause substantial physical disturbances to riparian areas. Classical biological control is being investigated as a means to manage this invasive weed. A fungus was identified that kills the shoot tips of growing giant reed canes, thereby reducing the amount of plants and plant material. The impact is a new biological agent that can reduce the growth and spread of giant reed, thus allowing areas to restore to their native vegetation.
Technical Abstract: A fungus was isolated consistently from dead shoot tips and flag leaves of Arundo donax L. (Poaceae) in France, Crete, Cyprus, Italy, Morocco, and Spain during April through September of 2003 to 2005. The fungus was identified as Nigrospora oryzae (Berk. & Br.) Petch (teleomorph Khuskia oryzae) using morphological characteristics (1). The mean diameters of 80 conidia obtained from sporulating plant specimens collected in France, Crete, and Cyprus were 14, 15, and 15 µm, respectively. The mean diameters of 25 conidiogenous cells and conidiophores were 7 µm and 4 µm, respectively. Identification was confirmed by comparing the sequence of the ribosomal DNA Internal Transcribed Spacer 1 and 4 regions from the France isolate (GenBank accession number DQ219433) with the sequence of a voucher specimen from the Museum National d'Histoire Naturelle, Paris, France. The isolate of N. oryzae from France was deposited at the CBS collection in Utrecht, Netherlands (CBS 113884). Nigrospora oryzae is known to be a weak pathogen on a wide range of plants but has never been reported previously on A. donax. The exact origin of A. donax is unknown, but U.S. populations are believed to be native to the Mediterranean region. Arundo donax is now a well-established weed in North America. Herein, N. oryzae is being investigated as a potential biological control agent of this weed in the U.S. Twenty young A. donax shoots growing in the greenhouse and 20 emerging canes in the field were selected based upon uniformity in size. A spore suspension in distilled water adjusted to 5 X 105 conidia/ml of the French isolate was prepared and 0.5 ml was injected with a syringe just below the growing point of the flag leaf in half of the greenhouse and field plants. The remaining plants were injected with 0.5 ml of distilled water as controls. Infection and death of the flag leaf occurred in 30% of the shoots in the greenhouse and 50% of the canes in the field after 21 days from inoculation. No disease occurred in the control plants. Greenhouse inoculation tests were repeated once. Nigrospora oryzae was reisolated from symptomatic tissues of inoculated shoots satisfying Koch's postulate. Attempts made to induce disease symptoms by applying spore suspensions on the whorl of leaves surrounding the apical tip failed. This is an indication that an insect vector may be needed to carry and deposit N. oryzae spores into the tight, whorled flag leaf for infection and disease development to occur. This is the first report of the pathogenicity of N. oryzae on A. donax.