Alexandre Bosco de Oliveira

As plantas daninhas competem com as culturas por fatores limitantes do meio em que vivem, portanto, estudos que apontem a resposta germinativa de sementes submetidas a estresses artificiais são importantes para entender a capacidade de sobrevivência e adaptação destas espécies sob condições de estresse naturais. Objetivou-se neste trabalho avaliar o efeito das condições salinas e térmicas sobre a germinação e vigor de sementes de Amaranthus deflexus L. Foram instalados dois experimentos, com semeadura realizada em placas de petri contendo duas folhas de papel de filtro umedecidas com água destilada (controle) ou com soluções de NaCl. No experimento 1 utilizou-se o delineamento experimental inteiramente casualizado (DIC), em esquema fatorial 2 x 6, constituído de dois fotoperíodos (12h luz e 24h escuro) e seis níveis de estresse salino (0; -0,3; -0,6; -0,9; -1,2 e -1,5 MPa), totalizando doze tratamentos, com quatro repetições. Ao final do teste, as sementes que não germinaram foram lavadas e colocadas em substrato papel toalha, umedecido com água para hidratação e estimular o processo germinativo. No experimento 2 utilizou-se um DIC com oito tratamentos (germinação sob 20; 25; 30; 35; 40°C, 20/30; 25/35 e 30/40°C) e quatro repetições cada. O estresse salino afetou negativamente o vigor das sementes de A. deflexus desde o nível de estresse de -0,3 MPa. O vigor das sementes foi comprometido pela ausência de luz, independentemente dos níveis de estresse aplicados. Houve superioridade na percentagem final de germinação e o índice de velocidade de germinação das sementes de A. deflexus na temperatura de 25°C constante e no regime alternado de 25-35°C. O procedimento multivariado discriminou os tratamentos 1 e 2 como superiores no dendograma A, bem como 4, 5 e 6 no dendograma B, configurando-se como método robusto para inferência em experimentos fatoriais sobre o comportamento germinativo.

This study aimed to characterize the behavior of different cultivars of Vigna unguiculata L. Walp. to osmotic stress, from germination to vigor parameters. The experimental design used was completely randomized in a 14 × 4 factorial arrangement, with fourteen cultivars and four levels of osmotic potential (0, −0.1, −0.2, and −0.4 MPa) of the germination solution. BRS-Novaera and BRS-Pajeú cultivars were characterized with possible tolerance at both the −0.1 and −0.2 MPa levels. The study pointed to the BRS-Pujante cultivar as the most sensitive to the −0.4 MPa level. The multivariate technique used allowed for a satisfactory characterization of the treatments adopted.

This study evaluate growth, gas exchange, solute accumulation and activity of antioxidant enzymes in dwarf cashew clones subjected to salinity. Shoot dry mass reduced 26.8% (CCP06) and 41.2% (BRS189) at 16 dS m-1, concerning control. For net photosynthesis, CCP06 and BRS189 presented 69.8% and 34.7% of reduction, respectively. Na+ and Cl- contents increased in leaves and roots, in both clones, although CCP06 leaves presented Na+ concentrations lower than those of BRS189, the first one was the clone that the most accumulated such toxic ion, whereas K+ content remained almost unchanged for both clones. Soluble N-amino was the organic solute that more varied with salinity in cashew seedlings. Salt stress increased the activity of superoxide dismutase in both clones, mainly 16 dS m-1 treatment. Additionally, salinity promoted increases in ascorbate and guaiacol peroxidase activities, and the last enzyme was the main involved in H2O2 removal. Despite the reductions in growth and gas exchange, dwarf cashew seedlings of both clones presented an osmotic adjustment mechanism, and an efficient enzymatic antioxidant system that were able to attenuate the salt and oxidative stress, respectively. Our research suggested that BRS189 clone is more tolerant to salt stress than CCP06.

Sugarcane grown in small rural properties of the Zona da Mata region, located in the southeast of the state of Minas Gerais (MG), is generally intended for animal feed and the production of rapadura, brown sugar, cachaça, and ethanol. This chapter focuses on the authors’ experience on technologies recommended to small farmers for the implantation and management of sugarcane plantations. The following issues are addressed and discussed: planning and preparation of the sugarcane plantation; soil sampling and soil fertility assessment; application of lime and gypsum; setting up seedling nurseries; green fertilization in the areas of planting and renewal of sugarcane plantation; soil preparation, planting and chemical fertilization of plant-cane; weed and pest control; chemical fertilization of ratoon; assessment of sugarcane nutritional status; organic fertilization with crop residues and agroindustrial residues; mineralization of sugarcane straw; assessment of broth quality and sugar production; and renewal of the sugarcane plantation.

This study aimed to investigate the allelopathic effects of Cyperus rotundus L. extracts on seed germination and early development of seedlings of Vigna unguiculata L. Walp. Alcoholic extracts at concentrations of 0, 1.5%, 3%, 4.5%, 6.0%, 7.5%, and 9.0% were obtained by crushing C. rotundus L. leaves used to moisten the "germitest" paper sheets. The data were subjected to analysis of variance and also both Tukey and Kruscal-Wallis tests were carried out at 5% for the data means. The first germination count, germination speed index, root length, shoot length, and dry root weight of cowpea were parametrically analyzed. The only variable with significance was first germination count. The germination reducted in relation to the control treatment around 10%. Thus, in the conditions used in this research, alcoholic extracts of C. rotundus L. did not affect either seed germination or early growth of cowpea seedlings.