O presente experimento foi realizado com o objetivo de estudar algumas possíveis modificações no tomateiro (Lycopersium sculentum, MILL), devidos à infecção virótica de uma estirpe do “vira-cabeça” e a influência do estado nutricional da referida planta na multiplicação do vírus. Para isso, foram conduzidos os seguintes trabalhos: a – Isolamento de uma estirpe do VVC; b - Estudo de algumas de suas propriedades (teste de envelhecimento, resistência ao dessecamento, ponto final de diluição, teste de inativação térmica e sintomas em tomateiro, N. glutinosa, fumo e feijoeiro manteiga); c - Determinação do peso seco das diversas partes de plantas doentes e sadias; d - Ensaios em solução nutritiva de HOAGLAND and ARNON completa ou com deficiência de macronutriente para estudo da multiplicação do VVC em plantas de tomateiros desenvolvidas nessas soluções. A estimativa de concentração do vírus foi feita através dos testes de lesões locais; e - Ensaios em solução nutritiva completa ou com deficiência de macronutrientes para estudo das deficiências associada ao VVC, determinando-se no final o teor dos nutrientes em pinas, pecíolos, caules e raízes de vários tratamentos; f - Estudo do aparecimento de sintomas do VVC no tomateiro associados à deficiência macronutrientes; g - Estudo ao microscópio ótico de algumas alterações celulares devidas a deficiência de macronutrientes e deficiência associada à presença do vírus; h- Exames ao microscópio eletrônico de algumas alterações na infra-estrutura celular de folhas de tomateiro com deficiência de macronutrientes e de plantas cultivadas em solução completa, afetadas pelo VVC.

The aim of the experiment described in this thesis was to study the effect of infection of a strain of Vira-cabeça virus (VCV), brazilian spotted wilt virus, in the tomato plants (Lycopersicum sculentum, MILL) on the chemical composition, infra-cellular structure and dry weight of the plant. Studied also was the influence of the nutritional level of the plant on the multiplication rate of the virus. The VCV strain used was from tomato plants naturally affected with the virus. It was obtained by inoculating the leaves of bean plants (Phaseolus vulgaris L., Manteiga var.) with juice extracted from infected tomato leaves. The local lesion produced in the Phaseolus vulgaris L., Manteiga var. was then transferred to tobacco plants for multiplication of the vírus. After six repetitions of the transfer, the strain was considered pure. The tomato plants were grown in various nutrient solutions, one of which the composition was complete for growth, each of the others lacked one essential macronutrient. The macronutrient content of the folioles, petioles, stems, and roots of the plants were determined and computed to the dry weight basis. Cellular alterations due to nutrient deficiencies, virus infection, or the combined effects of the two were followed in the optic and electronic microscopes. From the results obtained the following conclusions can be drawn; 1 - Virus multiplication in the the plants was reduced by a deficiency of each of the macronutrients. 2 - The moisture content of the tomato leaves was reduced by virus infection. 3 - Of the plants grown in nutrient-deficient solutions, those of the N-deficient (- N) medium only manifested local lesions of the VCV strain ; the P, K, and Mg-deficient (- P, - K, - Mg) plants showed few systemic symptoms; plants subjected to the combined treatments of phosphorus deficiency and VVC (- P + VCV) shed the lower leaves ; and the plants exposed to the combined treatment of (- K + VCV) infection developed increased necrosis in the leaf midrib. 4 - The folioles of plants grown in a - Ca medium were lower in nitrogen content than those of control plants grown in a complete nutrient medium; in a – N medium the folioles were lower in calcium content and higher in sulfur than those of control plants. 5 - In general the potassium content of the petioles was higher than other parts of the plant. When potassium was omitted from the nutrient solution, the magnesium content of the petioles increased and the potassium content decreased. 6 - The stems of the plants were lower in K content with the - N treatment than with any other; the roots of the plants were low in N content in the - P treatment, high in P content in the - N treatment, and high in magnesium content in the - K treatment. 7 - The N and K content of the petioles and the N content of the stems and roots of plants infected with VCV were higher than in hoalthy plants. In VCV infected plants, alterations occurred in the P and S content of the foliolos and calcium content of the petioles. 8 - At the cellular level, VCV caused a yellowing of the chloroplasts of the plants grown in complete nutriont solution and an increase in the lipid droplet formation in plants subjected to the following treatments: -N + VCV, -K + VCV and - S + VCV. 9 - Plants infected wi th VCV manifested modifications in the chloroplast structure, a reduction in the amount of grana and an increase in the lamelar system, and an increase in the number of mitochondria. 10 - All macronutrient-deficient nutrient solutions except - Mg produced changes in the chloroplasts. In the -Mg plants an accumulation of grains of starch and osmiophilic bodies occurred; in the - N and - P plants starch grains accumulated in the chloroplast; and in the - Ca plants th CW developed some gaps early in growth and were completely destroyed later.