C. G. Maciel,
M. F. B. Muniz,
P. M. Milanesi,
M. Lazarotto, and
E. Blume, Department of Plant Pathology, Federal University of Santa Maria, Brazil;
R. Harakawa, Biological Institute of São Paulo, Brazil;
L. R. S. Reiniger, Department of Crop Science, Federal University of Santa Maria, Brazil; and
F. A. Hamann, Institut für Nutzpflanzenwissenschaften und Ressourcenschutz (INRES) – Gartenbauwissenschaft Landwirtschaftliche Fakultät Rheinische Friedrich-Wilhelms-Universität Bonn, Germany
An elevated incidence of the fungal genus Fusarium was ascertained during a health quality analysis of a batch of Pinus elliottii Englm. seeds obtained from the Florestas Institute for Agricultural and Forest Research (Fundação Estadual de Pesquisa Agropecuária [FEPAGRO] Florestas) in Santa Maria (29° 39′ 55″ S and 53° 54′ 45″ W), state of Rio Grande do Sul, Brazil. This genus comprised about 75% of all fungal genera observed in a blotter test. The fungus was then isolated and purified to perform pathogenicity tests. Healthy seeds of P. elliottii were inoculated by contact with fungal mycelium for 48 h (3). Forty-two days after inoculation, a reduction was observed in the germination potential of the seeds; however, those seeds that germinated developed normally until, as seedlings, they suffered damping-off. Fusarium was isolated from the affected vegetal material by transferring mycelium tips to potato dextrose agar (PDA) medium in petri dishes in order to morphologically identify the species. After 72 h, a tan mycelial pad 5.5 cm in diameter had formed. After transfer to carnation leaf agar (CLA), pale orange sporodochia that formed macroconidia could be observed. The macronidia were relatively short and narrow (40.2 × 4.7 μm), each containing a mean of 5 septa; the apical cell was pointed, while the basal one was foot-shaped (2,4). The chlamydospores formed in clusters, while the conidiogenous cells could be seen on top of monophialides. Primer pairs ITS1 and ITS4, EF1-T and EF1-567R, and βtub-F and βtub were employed to amplify the three regions ITS1.8S ITS2, elongation factor – 1α (TEF 1-α), and β-tubulin, respectively. The sequences of these three regions showed 97, 95, and 99% of similarity with Fusarium sambucinum Fückel, respectively. The pathogen was reinoculated on P. elliottii seeds in order to complete Koch's postulates. The pathogenicity test was repeated with the same conditions described before and the results were confirmed. No occurrence of damping-off was observed in the control seedlings. The inoculated seedlings showed, besides damping-off, a visible reduction in root system expansion as well as reductions in fresh and dry tissue weight. F. sambucinum has already been reported on P. radiata D. Don in New Zealand, causing root rot and dieback (1); however, in Brazil, the present study is, to the best of our knowledge, the first to report the association of this pathogen with P. elliottii.
References: (1) M. A. Dick and K. Dobbie. N. Z. Plant Prot. 55:58, 2002. (2) W. Gerlach and H. Nirenberg. The Genus Fusarium – A Pictorial Atlas. Biologische Bundesanstalt für Land – und. Forstwirtschaft, Berlin, 1982. (3) M. Lazarotto et al. Summa Phytopathol. 36:134, 2010. (4) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual, 1st ed. Wiley-Blackwell, Hoboken, NJ, 2006.