LEAF PRIMORDIUM INITIATION AND EXPANDED LEAF PRODUCTION ARE COORDINATED THROUGH SIMILAR RESPONSE TO AIR-TEMPERATURE IN PEA (PISUM-SATIVUM L)

Accurate prediction of the timing of leaf area development is essentia l to analyse and predict the responses of crops to the environment. In this paper, we analyse the two processes determining the chronology o f 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 ra te during leaf development were induced by a,wide range of sowing date s and plant densities in glasshouse or field experiments. Full leaf ex pansion was found to occur one phyllochron after full leaf unfolding, whatever the leaf nodal position. Primordium initiation and expanded-l eaf production rates presented similar quantitative responses to air t emperature (linear response and common x-intercept), whatever the plan t growth rate, cultivar or period of cycle. As a consequence, they wer e co-ordinated and the numbers of initiated primordia or expanded leav es were easily deduced from simple visual observation of leaf unfoldin g. The change, over time, of the numbers of initiated leaf primordia a nd fully expanded leaves correlated with cumulated degree-days, with s table relationships in a wide range of environmental conditions. Two p hases, with different production rates. had to be considered. These re sults allowed us to predict accurately the beginning and the end of in dividual leaf development from daily mean air temperatures. The relati onships obtained were provide an effective way of analysing and predic ting leaf development responses to the environment. (C) 1997 Annals of Botany Company.