Influence of stress during soybean seed fill on seed weight, germination, and seedling growth rate

Water and high air-temperature (AT) stresses that occur during soybean (Glycine max (L.) Merr.) seed fill greatly reduce seed yield, but their effects on seed germination and vigor are less clear. The objective of this study was to determine the effect of water stress at optimum and high AT during seed fill on soybean seed yield and individual seed weight, and the subsequent germination and vigor of the seed. At daytime ATs of 27 and 35 °C in 1985 and 29 and 33 °C in 1986, control, moderate, and severe water-stress treatments were imposed by differential irrigation throughout seed fill on greenhouse-grown plants. Water stress intensity, measured by accumulating stress degree days (SDD) during seed fill, increased linearly as the volume of irrigation water declined. The weight and number of seed produced by each plant, and individual seed weight, declined linearly as SDDs accumulated at each AT. Water stress at optimum ATs reduced seed number more than individual seed weight, but water stress at high ATs reduced individual seed weight more than seed number. Water or high AT stress caused fewer larger seed and more small seed to be produced. The germination percentage and vigor of the harvested seeds was reduced by water stress and high ATs, but by a smaller proportion than yield or seed number. Individual seed weight, germination, and seedling growth rate were strongly correlated when reduced by water and high AT stress. Severe stress during seed fill caused soybean plants to exceed their capacity to buffer seed number, shifting seed weight distributions towards a larger proportion of small seed, resulting in poor seed lot germination and vigor. Key words: Soybean, germination, vigor, drought, high temperature, heat stress </jats:p

Seleção de progênies de meio-irmãos de cenoura baseada em características de sementes Selection of carrot progenies based on seed characteristics

A menor germinação e emergência de plântulas em campo de cenoura obtida nas sementes de cultivares nacionais em relação às importadas, aumenta o custo de produção além de impossibilitar a otimização do estande final através do emprego de semeadeiras de precisão. Setenta e quatro progênies de meio-irmãos oriundas de uma população de cenoura tipo Brasília foram avaliadas quanto a germinação, vigor e peso de sementes com o objetivo de verificar a variabilidade e as relações genéticas entre os referidos caracteres. Evidenciou-se a existência de diferenças significativas entre as progênies de meio-irmãos em relação a todos os caracteres avaliados. Os altos valores de herdabilidade e variabilidade genética entre progênies para os caracteres avaliados sugerem que métodos de melhoramento simples combinados com métodos de seleção tendo por base a teoria de índice podem ser aplicados visando a melhoria da qualidade fisiológica das sementes de cenoura.<br>Low seed germination and stand establishment of carrot seeds from Brazilian cultivars generally increase the production cost and impairs the use of precision seeders. Germination, vigor and seed weight of 74 progenies from a population of carrot cv. Brasilia were evaluated to verify the variability and the genetic relations among these three characteristics. Significant differences were observed among the progenies in relation to all characteristics. High values of heritability and genetic variability among progenies suggests that simple breeding methods combined with index selection methods may be applied during breeding programs in order to increase the physiological seed quality of carrot