03829nam a2200493 a 450000100080000000500110000800800410001910000200006024500890008026000410016930000100021049000190022052025500023965000120278965000120280165000130281365000220282665000230284865000120287165000190288365000150290265000180291765000110293565000260294665000150297265000180298765000130300565000220301865000180304065000180305865000270307665000240310365000210312765300230314865300190317165300210319065300120321165300260322365300140324965300210326365300220328465300110330665300180331716513912023-11-16       1983    bl uuuu  m   00u1 u    #d1 aPORTO. M. C. M.  aPhysiological mechanisms of drought tolerance in cassava (Manihot esculenta Crantz).  aArizona: University of Arizonac1983  a114p.  aTese Doutorado  aThe response of cassava (Manihot esculenta Crantz) to water stress was evaluated in two experiments conducted in Tucson, Arizona and Santander de Quilichao, Colombia, involving five cultivars (Mven 218, CMC 40, MCol 22, Mita 1158 and MCol 1684). In both experiments stress was imposed in a given stage of the plant cycle. A third experiment, conducted in Palmira, Colombia, evaluated the relationship existng between photosynthesis, relative humidity and yields of cassava. Cultivar MCol 1684 reduced its transpirating area by either reducing leaf formation (stress given to 3-month-old plants) or increasing leaf fall (6-month-old plants). A reduction in plant growth and leaf expansion rates is attributed to reducing the plant's total leaf area. Water stress imposed in Tucson also showed reductions in plant growth, leaf formation, extension and final leaf size (except for MVen 218). Plants of MCol 1684 in Santander de Quilichao, like MVen 218 in Tucson, did not change their final leaf leaf sizes due to stress. Dry matter production was more reduced when stress was imposed early in the plant growth cycle. Dry matter partitioning was also altered by stress given to 3-month-old plants of MCol 1684. The stressed plants delayed the allocation of dry matter to the storage roots. Noon and afternoon values of leaf coductance and transpiration of MCol 1684 were reduced after 40 days of stress. Interestingly, leaf temperatures of non-stressed plants were higher than those of the stressed plants. This can be attributed to an increase in leaf reflectance in the stressed plants by changing the angle of orientation of their leaves in relation to the sun. Leaf coductances of non-stressed plants were correlated to photosynthesis, leaf temperatures and vapor pressure deficits in measurements taken at 3:00 PM. In the stressed plants conductances were also correlated to photosynthesis leaf temperatures, air moisture and transpiration. Leaf water potentials were slightly reduced by stress in Tucson, except for MVen 218. Plants of MCol 1684, in Quilichao, did not show significant reduction in L due to stress. In contrast, noon and mid-afternoon values of L were lower in the non-stressed plants after 30-40 days of treatment. This suggests the occurrence of higher daily water stresses in non-stressed plants, because of elevated transpiration rates. The effect of air humidity on the stomatal functioning of MCol 1684 seems to be strong, as proved the dependence of transpiration, conductances and photosynthesis on relative humidity.  aArizona  acassava  aColombia  adrought tolerance  adry matter content  aManihot  aphotosynthesis  aphysiology  aUnited States  ayields  aDeficiência Hídrica  aFisiologia  aFotossíntese  aMandioca  aManihot Esculenta  aMatéria Seca  aProdutividade  aRelação Água-Planta  aResistência a Seca  aUmidade Relativa  aDrought resistance  aEstados Unidos  aEstresse hidrico  aPalmira  aPlant water relations  aQuilichao  aRelative umidity  aTolerancia a seca  aTucson  aWhater stress