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Foliar and Cane Rot of Arundo donax Caused by Nigrospora oryzae in Europe

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 from April of 2003 through September of 2005. The fungus was identified as Nigrospora oryzae (Berk. & Br.) Petch (teleomorph Khuskia oryzae) on the basis of morphological characteristics (1). The mean diameter 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 and 4 μm, respectively. Identification was confirmed by comparing the sequence of the ribosomal DNA internal transcribed spacer 1 and 4 regions from the French isolate (GenBank Accession No. 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, the Netherlands (CBS 113884). N. oryzae is known to be a weak pathogen on a wide range of plants but has not been reported on A. donax, which is now a well-established weed in the United States and North America, probably originating from the Mediterranean Region. Herein, the possible use of N. oryzae as a biological control agent was investigated. Twenty young A. donax shoots growing in the greenhouse and 20 emerging canes in the field were selected on the basis of uniformity in size. A spore suspension in distilled water adjusted to 5 × 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 onehalf 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 21 days from inoculation. No disease developed on the control plants. Greenhouse inoculation tests were repeated once. N. oryzae was reisolated from dead leaves and the terminal node 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. To our knowledge, this is the first report of foliar and cane rot of A. donax caused by N. oryzae.

References: (1) K. H. Domsch et al. Page 515 in: Compendium of Soil Fungi. IHW-Verlag, Eching, Germany, 1993.