Abstract
The experiment was carried out at the Embrapa Semi-Árido, Petrolina-PE, Brazil, in order to study the physiological responses of umbu plants propagated by seeds and by stem cuttings under water stress conditions, based on leaf water potential and gas exchange measurements. Data were collected in one-year plants established in pots containing 30 kg of a sandy soil and submitted to twenty-day progressive soil water deficit. The evaluations were based on leaf water potential and gas exchange data collection using psychrometric chambers and a portable infra-red gas analyzer, respectively. Plants propagated by seeds maintained a significantly higher water potential, stomatal conductance, transpiration and photosynthesis under decreasing soil water availability. However, plants propagated by stem cuttings were unable to maintain a favorable internal water balance, reflecting negatively on stomatal conductance and leaf gas exchange. This fact is probably because umbu plants propagated by stem cuttings are not prone to formation of root tubers which are reservoirs for water and solutes. Thus, the establishing of umbu plants propagated by stem cuttings must be avoided in areas subjected to soil water deficit.
Highlights
Plants propagated by seeds maintained the leaf water potential significantly higher those from stem cuttings (Figure 2)
Leaf water potential of plants propagated by seeds reached -0.56 MPa and -0.88 MPa, respectively, in the fourth and in the twentieth day, meaning a 0.16 MPa drop in the period while values obtained with plants from stem cuttings decreased from -0.72 MPa to -1.3 MPa, meaning a difference of about 0.58 MPa
Lima Filho (2001) observed that during the dry season early morning leaf water potential of adult umbu plants propagated by seeds declined from -0.73 MPa at predawn to about -0.97 MPa at 8:00 h, meaning a 0.24 MPa difference
Summary
The survival of the species under water stress conditions is assured by rigid stomatal control on transpiration (Lima Filho & Silva, 1988) and by specialized root system bearing tubers, whose function is to store water, minerals and other solutes ( Lima Filho, 2001). These resources are used during the dry season for maintaining plant normal metabolism and the initiation of the flowering process. It has been stated that umbu plants propagated by stem cuttings are not prone to formation of root tubers (Nascimento et al, 1993), what may imply on low survival when transplanted to the field. This paper was carried out in order to study the physiological behavior of umbu plants propagated by seeds and by stem cuttings, under progressive soil water stress, based on leaf water potential and gas exchange measurements
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