INFLUENCE DE LA TEMPERATURE DU SUBSTRAT ET DE LA FERTILISATION AZOTEE SUR LA CROISSANCE, LE DEVELOPPEMENT, LA TENEUR EN AZOTE ET L’ACTIVITE DE LA NITRATE REDUCTASE CHEZ LA TOMATE

Abstract

We measured the effects of five root temperatures (12, 18, 24, 30 and 36 °C) and five rates of nitrogen fertilization (0, 2.5, 7.5, 22.5 and 67.5 meq N∙L−1) on growth, development, nitrogen content and nitrate reductase activity of tomato plants (Lycopersicon esculentum Mill. ’Vendor’). The greatest root dry weight was obtained at 18 °C and 2.5 meq N∙L−1 and the highest shoot dry weight at 24 °C and 22.5 meq N∙L−1. Total fruit weight was maximum at 24 °C and 2.5 meq N∙L−1. High root temperatures and high levels of fertilization increased the number of aborted flowers and the nitrogen content of shoots, but reduced tomato yields. Nitrate reductase activity (NRA) was higher in leaves than in roots and with plants receiving 22.5 meq N∙L−1 as compared to 2.5 meq. NRA in roots decreased as temperature increased.Key words: Lycopersicon esculentum Mill., root zone temperature, nitrate reductase, nitrogen