A influência do stress hídrico e da eutrofização do solo na doença da murchidão do pinheiro

Tese de mestrado. Biologia (Biologia da Conservação). Universidade de Lisboa, Faculdade de Ciências, 2013Pine wood nematode (Bursaphelenchus xylophilus) is the causal agent of pine wilt disease. Due to the high mortality and speed with which this disease can spread it is considered one of the biggest threats to pine trees in the world. It causes considerable economic and environmental damage, severely changing forest composition. Pine wood nematode is dependent on an insect vector of the genus Monochamus for short range transmission and on the timber industry for long range transmission. This work seeks to study the development of pine wilt disease in P. radiata and P. pinaster under water stress at a moderate temperature (20ºC), which is considered to be the limit for the development of the disease. It also seeks to study the effects of soil eutrophication in P. pinaster in combination with high temperature (25ºC). For that, a greenhouse experiment was carried out using both pine species plants directly infected by Bursaphelenchus xylophilus. Throughout this study various physiological parameters and the symptomology were observed to determine whether any of the physiological parameters would permit the disease to be detected before the appearance of visible symptoms. This study showed that water stress is an important factor in the development of pine wilt disease, although with a different degree in each pine species. For P. pinaster, water stress resulted in a mortality of 37.5%; however, for P. radiata water stress had a much stronger effect, resulting in a 75% mortality. Soil eutrophication does not seem to have any effect on the evolution of the disease, given that all treatments expressed a similar development of the disease and similar mortality (between 12,5-25%). However, the relative small number of individuals that developed the disease prevents solid conclusions. Moreover, none of the physiological parameters observed during this study allowed the detection of pine wilt disease before the onset of symptoms occurred.O nemátode da madeira do pinheiro (Bursaphelenchus xylophilus) provoca a doença da murchidão do pinheiro. Devido à grande mortalidade e à rapidez com que esta doença se pode espalhar é considerada uma das maiores ameaças para os pinheiros no mundo. Provoca graves danos económicos e ecológicos, alterando fortemente a composição florestal. O nemátode do pinheiro está dependente de um insecto vector do género Monochamus, para a sua transmissão a curta distância, sendo o comércio da madeira a principal causa da sua transmissão a longa distância. Neste trabalho procurou-se estudar o desenvolvimento da doença da murchidão do pinheiro, em P. radiata e P. pinaster, sobre stress hídrico, a uma temperatura moderada (20ºC), considerado como o limite para o desenvolvimento da doença da murchidão do pinheiro. Também se procurou estudar o efeito da eutrofização do solo, em P. pinaster, a uma temperatura elevada (25ºC). Para esse fim, foi realizada uma experiência em estufa utilizando indivíduos de ambas as espécies directamente infectados com Bursaphelenchus xylophilus. Neste estudo observou-se vários parâmetros fisiológicos e a sintomatologia, para se determinar se algum destes parâmetros fisiológicos permite detectar a doença antes do aparecimento de sintomas visíveis. Pôde-se observar que o stress hídrico é um factor muito importante no desenvolvimento da doença, mas com um grau diferente para cada espécie. Em P. pinaster, o stress hídrico resultou numa mortalidade de 37,5%, enquanto em P. radiata o stress hídrico teve um efeito muito mais acentuado, resultando numa mortalidade de 75%. A eutrofização do solo não parece ter afectado a evolução da doença, tendo todos os tratamentos apresentado uma evolução da doença e mortalidade semelhantes (entre 12,5-25%), mas o pequeno número de indivíduos que desenvolveram a doença impossibilita conclusões definitivas. Nenhum parâmetro fisiológico utilizado neste trabalho permitiu detectar a doença antes de esta apresentar sintomas visíveis

Seedling emergence of five varieties of citric rootstocks grown in environments with different levels of shading

The emergence of citrus seedlings is influenced by several factors. One is the degree of brightness. The objective of the experiment was to evaluate the influence of four environments in the emergence of seedlings of five citrus varieties rootstocks. The work was carried out on private property located in the city of Alegre-ES, located at 20° 49’ south latitude and 41° 32’ west longitude and 322 m altitude. The experimental design was completely randomized in a split plot, with four rooms consisting of 0, 30, 50 and 80% shading in the plot and five varieties of rootstocks subplots, with four repetitions and twenty-five seeds per replicate. The rootstocks used were the Rangpur lime, lemon Volkameriano, Poncirus trifoliata, ‘Swingle’ citrumelo and Flying Dragon. After 60 days of sowing, emergence rate index, emergence percentage, leaf number and height were evaluated. At 124 days, leaf area, total chlorophyll (a + b), root dry mass and shoot were evaluated. The citric rootstocks tested responded differently when subjected to shading, and can use physiological and morphological mechanisms to maintain or even improve the emergence and seedling vigor. It was observed that the P. trifoliata rootstock obtained better performance when compared to others and that 50% shading can be adopted in this stage of citrus seedling production since it reduces seedling time in the tubes and does not affect the seedling quality