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Elongation rate of sorghum leaves has a common response to meristem temperature in diverse african and European environmental conditions

Lafarge T., De Raïssac M., Tardieu F.. 1998. Field Crops Research, 58 : p. 69-79.

DOI: 10.1016/S0378-4290(98)00085-9

We have tested whether thermal time can account for the effect of meristem temperature on leaf appearance rate (LAR) and leaf elongation rate (LER) of sorghum in a wide range of conditions without water or nutrient deficit. This requires that responses to temperature should be consistent in different locations and different seasons, and that responses of LER of different leaves of the plant should be similar. Sorghum plants (Sorghum bicolor (L,) Moench., cv. E-35-1) were sown in the field in Bamako (Mali) from October 1995 to August 1996, in Montpellier (France) in summers 1995 and 1997, and in a growth chamber. Irradiance, air and meristem temperatures (Tm) and air humidity were measured together with LER in all experiments. Unique and light relationships were observed between Tm and LER of leaves located at different positions on the stem, for all experimental conditions when evaporative demand was low (meristem-to-air vapor pressure deficit, VPDma, lower than 2.5 kPa). Relationship, remained linear over the whole studied range of Tm i.e. 13-32.C (R2, from 0.7 to 0.87). With high evaporative demand, LER was lower than the LER expected at the same temperature but with low VPD ma (LERreg); the normalized difference between LER measured on a given day (LERa) and LERreg was linearly related to VPDma (R2=O.52). A linear relationship was also observed between Tm and LAR measured before the beginning of stem elongation when Tm, was lower than 27.C. The x-intercepts of relationship,., between Tm and LER or LAR did not differ in a covariance analysis, With a common value of 10.8.C. The use of thermal time witliout correction for high temperature or photoperiod was the most appropriate way to account for the timing of leaf development. It allowed prediction of LER provided that the reduction in LER due to evaporative demand was taken into account.

Mots-clés : sorghum bicolor; croissance; feuille; température; méristème

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