Fertilization in citrus is a cultural practice with great importance as it affects significantly the quality of fruit. In this work we evaluated the effects of organic versus conventional farming systems on internal and external characteristics of citrus, with particular emphasis on vitamin C content. The study was carried out in different orchards of the Algarve region, in the south of Portugal. Fruits of different orchards were harvested at physiological maturity and submitted to physical and chemical analyses. The results showed that mineral fertilization led to fruits with greater weight and diameter, a thicker peel and a more intense colour. Compared with conventional production, fruits from organic farming had more soluble solids and a lower maturation index. The highest concentrations of vitamin C were recorded in fruits from organic farming, but the response depended on species and cultivar.

The cassava propagation system is slow and favors disease transmission through successive generations. Micropropagation is an alternative to overcome the aforementioned limitations, besides allowing the generation of a larger number of pest- and pathogen-free plants. Therefore, the aim of the present study is to investigate the effect of culture media on the multiplication in vitro of five wild Manihot species. The experiment followed a completely randomized design, at factorial arrangement 5 (wild Manihot species) x 6 (culture media), with 11 repetitions. Explants consisted in nodal segments (91 cm long and one lateral bud) of species Manihot flabellifolia, M. tristis, M. caerulescens, M. chlorosticta and M. jacobinensis, which were extracted in vitro from the collection of wild cassava species. One segment was placed in each test tube added with 10 mL of MS media 0.01, 17N, 12A3, 4E, 8S and WPM, and kept for 90 days in growth room under 30 μmol m-2 s-1irradiance, temperature 27 ± 1 °C and 16h photoperiod. Variables plant height (cm), number of green leaves, number of senescent leaves, number of shoots, number of microcuttings, fresh and dry shoot mass, fresh and dry root mass (mg) and callus mass (mg) were analyzed. Our results showed that the culture medium 12A3 was not responsive to any of the species; however, if one takes into consideration variables plant height and number of microcuttings, this medium can possibly be used in the micropropagation of other wild species belonging to genus Manihot.

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A oxidação afeta o crescimento in vitro, em função da liberação de compostos fenólicos, resultando no escurecimento dos tecidos e, por consequência, na morte de explantes e de plantas. Diante disso, este trabalho teve como objetivo estudar o efeito do ácido ascórbico e do polivinilpirrolidona (PVP) no cultivo in vitro do inhame, visando a redução ou eliminação da oxidação dos explantes e a otimização do crescimento dos genótipos D. alata var. purpurea (Roxb.) A. Pouchet e D. rotundata Poir. Nesse experimento, segmentos nodais de aproximadamente 1 cm de tamanho, extraídos de plantas previamente cultivados in vitro, foram introduzidas em tubos de ensaio contendo 10 mL de meio de cultura 2GGC, acrescido de 30 g L-1 de sacarose, solidificado com 2,2 g L-1 de Phytagel® e pH ajustado a 5,8 antes da autoclavagem. Ao meio básico foram acrescidos dois antioxidantes, compondo dois experimentos distintos. No primeiro experimento, foi utilizado o ácido ascórbico nas concentrações de 0 mg L-1; 25 mg L-1; 50 mg L-1; 75 mg L-1 e 100 mg L-1; e no segundo o PVP, nas doses de 0 mg L-1; 50 mg L-1; 100 mg L-1; 150 mg L-1 e 200 mg L-1. Cada experimento foi instalado em delineamento inteiramente casualizado, em esquema fatorial 5 x 2 (concentrações de antioxidante x genótipos), contendo 12 repetições por tratamento. Após 90 dias de manutenção em sala de crescimento, procedeu-se a avaliação do desenvolvimento das plantas e observou-se que os antioxidantes ácido ascórbico e polivinilpirrolidona não promoveram melhorias nas variáveis de crescimento.

The composition and physical state of the culture medium, as well as the effect of supplementation in different subcultures, are determining factors for the regeneration and good development of the in vitro explant. Therefore, this study aimed to study the effect of the culture medium on micropropagation during four subcultures, depending on the growth variables of the genotypes Dioscorea alata L., D. alata var. purpurea (Roxb.) A. Pouchet, and D. rotundata. Nodal segments of 1 cm length of plants previously cultivated in vitro were introduced into 10 mL of MS culture media supplemented with 100 mg L-1 of inositol, 20 mg L-1 of cysteine, 0.20 mg L-1 of ANA, 0.08 mg L-1 of AG3 and 0.05 mg L-1 of BAP and 2GGC basic, both in solid and liquid states plus 3 g L-1 of activated charcoal and 30 g L-1 of sucrose and the pH adjusted by 5.8 before autoclaving. At every 30 days of in vitro culture, development variables, percentage of responsive explants, and the number of calluses were evaluated. The MS and solid 2GGC media are the most suitable for the multiplication of the genotypes D. alata and D. alata var. purpurea. For the D. rotundata genotype, the solid MS medium is the most suitable for its in vitro multiplication.