Contribution to the study of shoot blight disease on stone pine (Pinus pinea L.)

Mestrado em Engenharia Florestal e dos Recursos Naturais - Instituto Superior de Agronomia

Until a few years ago, the stone pine (Pinus pinea) was a species affected by few pathogens, but recently shoot blight and death of the shoots have been frequently reported in our country, causing serious concerns for producers and pine nut industry. By hindering the development of cones, this problem affects the production of pine nuts, the main resource of this forest industry. Lately, fungi belonging to different genera have been identified associated with shoot blight of stone pine. Some of these fungi, such as Sydowia polyspora, were unknown in Portugal and others, although present in our country (eg Pestalotiopsis spp.), were usually considered weak or stress parasites, affecting only weakened trees. The main aim of the present work was to contribute for the identification of the fungi associated to shoot blight of stone pine and to clarify their role in the expression of the disease. A total of 46 isolates from seven different sites were analysed. Identification was made based on cultural and morphological characteristics and phylogenetic analysis (ITS, TEF and TUB regions). Isolates of the most relevant species were tested for their pathogenicity. This work allowed to identify several species of fungi associated with shoot blight in stone pine, namely: Diplodia sapinea, Epicoccum nigrum, Pestalotiopsis australis, Pestalotiopsis sp. and Sydowia polyspora. The inoculation of one year-old P. pinea plants under controlled conditions allowed to confirm the pathogenicity of isolates of species D. sapinea and Pestalotiopsis sp.. The role of S. polyspora in the expression of these symptoms was not clarified, however, in the plants inoculated simultaneously with D. sapinea and S. polyspora isolates, the incidence of the disease was much higher than in the plants inoculated with D. sapinea alone, raising the hypothesis that S. polyspora may be potentiating the pathogenicity of D. sapinea. In this work, the fungus S. polyspora was identified for the first time in Portugal and for the first time in stone pine. It should also be pointed out that the isolate belonging to Pestalotiopsis sp., whose pathogenicity was proved in the present work, presents morpho-cultural and genetic characteristics different from those described for other species within this genus, being more aggressive than other known species within this genus

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