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Can cassava cells cope when water is withheld?
The effects of water deficit on plant growth are particularly felt in dryland crops where yields are often reduced because of periodic or chronic drought. In defining objectives for plant breeding it is important to have clear information on a plant’s response to drought and on its ability to recover. This has been the subject of research carried out on cassava (Manihot esculenta) by Alfredo Alves from Bahia, Brazil and Tim Setter, Cornell University, USA (pp. 605–613). They have focused on leaf development during 8 days of water stress followed by re-watering. Water stress was imposed by allowing soil to dry to 30 % of field capacity and maintaining the water content at this level. The results show very interesting differences in the effects of water deficit on leaves of different ages, ranging from early leaf meristems to leaves growing just by cell expansion. It was clear that water deficit affected both cell division and cell expansion but that both exhibited some capacity for recovery after re-watering. In leaf meristems, recovery was complete although there was delay in re-watered plants in the attainment of normal size of leaves derived from these meristems. In young leaves, growing by rapid division and some expansion, water deficit inhibited both processes, and on re-watering both recovered partially so that at maturity leaves had fewer and smaller cells than controls. Finally, in leaves growing only by rapid expansion, growth was again brought to a halt by water deficit and, again, recovery was only partial: leaves of re-watered plants had smaller cells than control plants. Loss of leaf area affects the overall photosynthetic capacity of the plant and thus influences yield. It is thus important to continue these studies in order to understand why, except in meristems, recovery from the effects of water deficit is only partial.
Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
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