Effet de la dose de semis et de l’écartement entre les rangs sur l’interférence entre le Chenopodium album et le Triticum aestivum

Un essai répété 4 années a permis d'évaluer l'effet de la présence du chénopode (Chenopodium album) sur la productivité du blé (Triticum aestivum 'Max'). La céréale a été ensemencée à cinq doses de semis (100, 200,300, 400 et 500 grains viables m-2) et à deux écartements entre les rangs (10 et 18 cm). Une réduction de l'écartement entre les rangs a permis d'accroître les rendements en blé de 16 % en présence ou non du chénopode. La dose de semis est un facteur plus important que l'écartement entre les rangs. À une dose de semis de 100 grains m-2, la présence du chénopode a causé une réduction du rendement en grain de 23 % tandis que cette réduction était de 11 % avec une dose de semis de 500 grains m-2. La baisse de rendement en blé provoquée par la présence de chénopode est surtout attribuable à une réduction du nombre d'épis par unité de surface. Le chénopode a également réduit le nombre d'épis par plant et le nombre de grains par épi tandis que le poids de 1000 grains et l'indice de récolte ont été peu affectés. Les contenus en azote et en phosphore du grain de blé ont été réduits par la présence du chénopode. Une réduction de l'écartement entre les rangs ou une augmentation de la dose de semis du blé n'a pas permis de réduire le nombre de plants mais a réduit la biomasse du chénopode.A 4-yr study was conducted to evaluate the effect of two row spacings (10 and 18 cm) and five seeding rates (100, 200, 300, 400, and 500 viable seeds m-2) of wheat (Triticum aestivum 'Max') on the interference between lamb's-quarters (Chenopodium album) and the crop. Narrow row spacing increased wheat yield by 16% regardless of the presence or absence of lamb's-quarters. Seeding rate was a more important factor than row spacing. At a seeding rate of 100 seeds m-2, the yield reduction caused by lamb's-quarters was 23% whereas it was 11 % when wheat was seeded at 500 seeds m-2. Yield reductions were attributed to a decrease in the number of spikes m-2. Lamb's-quarters also reduced the number of spikes per plant and the number of kernels per spike, and, to a lesser extent, the 1000 kernel weight and the harvest index. Nitrogen and phosphorus content of wheat grain were reduced by the presence of Chenopodium. High seeding rates or narrow row spacing did not reduce the density of lamb's-quarters but did reduce the weed biomass

Metabolic response to a ketogenic breakfast in the healthy elderly.

OBJECTIVE: To determine whether the metabolism of glucose or ketones differs in the healthy elderly compared to young or middle-aged adults during mild, short-term ketosis induced by a ketogenic breakfast. DESIGN AND PARTICIPANTS: Healthy subjects in three age groups (23 +/- 1, 50 +/- 1 and 76 +/- 2 y old) were given a ketogenic meal and plasma beta -hydroxybutyrate, glucose, insulin, triacylglycerols, total cholesterol, non-esterified fatty acids and breath acetone were measured over the subsequent 6 h. Each subject completed the protocol twice in order to determine the oxidation of a tracer dose of both carbon-13 (13C) glucose and 13C-beta-hydroxybutyrate. The tracers were given separately in random order. Apolipoprotein E genotype was also determined in all subjects. RESULTS: Plasma glucose decreased and beta-hydroxybutyrate, acetone and insulin increased similarly over 6 h in all three groups after the ketogenic meal. There was no significant change in cholesterol, triacylglycerols or non-esterified fatty acids over the 6 h. 13C-glucose and 13C-beta-hydroxybutyrate oxidation peaked at 2-3 h postdose for all age groups. Cumulative 13C-glucose oxidation over 24 h was significantly higher in the elderly but only versus the middle-aged group. There was no difference in cumulative 13C-beta-hydroxybutyrate oxidation between the three groups. Apolipoprotein E (epsilon 4) was associated with elevated fasting cholesterol but was unrelated to the other plasma metabolites. CONCLUSION: Elderly people in relatively good health have a similar capacity to produce ketones and to oxidize 13C-beta-hydroxybutyrate as middle-aged or young adults, but oxidize 13C-glucose a little more rapidly than healthy middle-aged adult