Natural selection for grain yield in dry bean populations bred by the bulk method

Three dry bean harvests are possible in some regions of Brazil that differ significantly in temperature, rainfall and day length conditions. Thus in breeding programs, generation advance using the bulk method can be carried out in these three periods. It is questionable whether under conditions such as these the action of natural selection would contribute to an increased frequency of individuals considered superior by breeders. The present study assessed six segregating populations, for up to 17 successive generations to check the effects of natural selection during inbreeding. Six populations were generated from a partial diallel: one group consisting of two early maturity cultivars, ESAL 686 and Manteigão Fosco was crossed to a second group of three cultivars with medium maturity, Carioca MG, Milionario and Ouro. The six populations plus the five parents were assessed in experiments using a randomized complete block design, in three locations: Lavras, where in breeding started from the F₂ generation; Lambari and Patos de Minas, from the F₃ generation. A linear regression equation was fitted to the parents and hybrids mean data in each location, considering grain yield as the dependent variable (y) and generations (F₂ = 1, F₃ = 2, etc.) as the independent variable. Genetic progress was estimated from the differences between the linear regression coefficients of the hybrids (b_i)and the mean of the b coefficient of their respective parents (b_j). The (b_i-b_j) were positive in all cases, showing that natural selection acted in all the segregating populations and contributed to an average increase in grain yield of 2.5% per generation over the mean of the parents.     

Accompanying ions of ammonium sources and nitrate : ammonium ratios in tomato plants

The tomato (Solanum lycopersicum L.) cultivar Micro‐Tom (MT) is widely used in physiological studies, but the effects of nitrate ( ) and ammonium ( ) ratios ( : ratios) and, in particular, the effects of the accompanying ions in sources are unknown. To determine whether the accompanying ions in sources influence toxicity, the effects of : ratios on the physiology, electrolyte leakage index, nutrition, and dry weight were studied using hydroponics. The sources were ammonium chloride (NH₄Cl) or ammonium sulfate [(NH₄)₂SO₄], and five : ratios were used: 100 : 0, 75 : 25, 50 : 50, 25 : 75, and 0 : 100. The source was calcium nitrate [Ca(NO₃)₂], and the nitrogen (N) concentration was 15 mmol L^?1. The results indicate that NH₄Cl or (NH₄)₂SO₄ can be used in studies on toxicity because the accompanying ions did not influence the tomato plants. In addition, : ratios of 100 : 0 and 75 : 25 resulted in the highest dry weight of tomato plants, whereas ratios of 25 : 75 or 0 : 100 were toxic.     

Atmospheric CO2 concentrations over the last glacial termination

A record of atmospheric carbon dioxide (CO2) concentration during the transition from the Last Glacial Maximum to the Holocene, obtained from the Dome Concordia, Antarctica, ice core, reveals that an increase of 76 parts per million by volume occurred over a period of 6000 years in four clearly distinguishable intervals. The close correlation between CO2 concentration and Antarctic temperature indicates that the Southern Ocean played an important role in causing the CO2 increase. However, the similarity of changes in CO2 concentration and variations of atmospheric methane concentration suggests that processes in the tropics and in the Northern Hemisphere, where the main sources for methane are located, also had substantial effects on atmospheric CO2 concentrations.