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Résumé :
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Accurate prediction of the timing of leaf area development is essential to analyse and predict the responses of crops to the environment. In this paper, we analyse the two processes determining the chronology of leaf development-initiation of leaf primordia by the shoot meristem and production of expanded leaves out of the shoot tip-in several pea (Pisum sativum L.) cultivars in response to air temperature and plant growth rate. Contrasting levels of air temperature and plant growth rate during leaf development were induced by a,wide range of sowing dates and plant densities in glasshouse or field experiments. Full leaf expansion was found to occur one phyllochron after full leaf unfolding, whatever the leaf nodal position. Primordium initiation and expanded-leaf production rates presented similar quantitative responses to air temperature (linear response and common x-intercept), whatever the plant growth rate, cultivar or period of cycle. As a consequence, they were co-ordinated and the numbers of initiated primordia or expanded leaves were easily deduced from simple visual observation of leaf unfolding. The change, over time, of the numbers of initiated leaf primordia and fully expanded leaves correlated with cumulated degree-days, with stable relationships in a wide range of environmental conditions. Two phases, with different production rates. had to be considered. These results allowed us to predict accurately the beginning and the end of individual leaf development from daily mean air temperatures. The relationships obtained were provide an effective way of analysing and predicting leaf development responses to the environment. (C) 1997 Annals of Botany Company.
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