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Pour concevoir des itineraires techniques permettant d'obtenir une faible teneur en nitrate des laitues, il est necessaire de mieux comprendre les effets des conditions de culture sur la croissance et l'accumulation de nitrate dans la plante. L'objectif de cette etude est d'analyser l'effet de la nutrition azotee sur l'efficience d'interception et de conversion du rayonnement en matiere seche, et sur l'accumulation de nitrate et d'eau dans la laitue, pour differentes conditions de temperature et de rayonnement. La croissance des laitues et les concentrations en eau et en nitrate ont ete mesurees sur deux cultures hors-sol (en ete et en automne) avec deux niveaux de rayonnement incident et de nutrition azotee. L'efficience de conversion de l'energie lumineuse en matiere seche (RUE) etait comprise entre 2.12 et 3.5 g.MJ -1 . Elle etait plus elevee pour les faibles rayonnements et les forts niveaux de nutrition azotee. Une correlation positive entre les teneurs en nitrate et en eau a ete observee. Cette relation, dont la pente n'est pas affectee par les conditions de croissance, semblerait indiquer une forte interdependance des accumulations d'eau et de nitrate chez la laitue.

Groundnut flowering was analyzed on plants whose growth was modified by changing planting density or by shading exposure during different periods of the growth cycle. Flowering was assessed at the level of the plant, branch, and inflorescence. The results showed that flowering progression along the branch reflected the flowering dynamics of the entire plant. The number of flowers produced was determined by the rate of progression of flowering along the branches and by the period from the beginning to the end of blooming. These features were closely dependent on plant growth conditions. Increasing the planting density slowed the flowering rate and shortened the blooming period. This allowed a better synchronization of pod maturity. Exposure to shade before flowering decreased the rate of production of flowers but prolonged its duration, whereas exposure at mid-flowering halted flower production. It is suggested that the different reproductive organs (flowers and pods) may compete for assimilates, thus explaining the various effects observed on daily flower production.

International audience; Physiological quality of pea (Pisum sativum L.) seed depends on various factors affecting the plant, including water supply, the effect of which has not been fully characterized. The effects of different periods of water stress during reproductive stages on the seed yield and seed physiological quality were investigated in field studies for 3 yr (1991, 1992, and 1993) at Brain-sur-l'Authion, France, on a Mollisol, Rendoll, eutrochreptic soil. Irrigation during seed filling (IDSF) and irrigation during the period from the start of flowering to the start of seed filling were compared with a non-irrigated (NI) and a season-long, irrigated-as-needed (WI) treatment. The physiological quality of pea seeds was assessed by germination percentage and the conductivity and cold tests. The germination percentage averaged 98% and was not modified by water stress. In 1993, rainfall during the reproductive stages was high, and there were no differences in seed yield or quality between treatments. In 1991 and 1992, the rainfall was much lower, and the NI treatment showed the lowest seed yield and quality as far as the conductivity test and cold test were concerned. The WI treatment showed the best yields. Water stress during the flowering period did not reduce seed quality more than WI, and reduced seed yield only slightly. Water stress during seed filling decreased seed yield but the effect on seed quality was not significant. Individual seed weight was higher and less variable in IDSF treatments than in WI treatments. Changing irrigation strategies for pea seed production by irrigating during seed filling may improve the physiological quality of the seedlots without decreasing the seed yield.