Revista Brasileira de Milho e Sorgo (Dec 2005)
WATER STRESS CHARACTERIZATION OF TWO MAIZE (Zea mays L.) INBRED LINES WITH SAP FLOW PROBES
Abstract
The partial replacement of the plants water requirements and the selectionof better genotypes adapted to the water shortage conditions can contribute to the increaseof water availability in the agriculture. Although the effects of water stresses on the cropdevelopment are known, few reliable methodologies used for its characterizations basedon parameters directly related to the plants exist, aiming to maintain good productivitylevels and to increase the tolerance to water deficiency, mainly due to the difficulties ofenvironmental control of water factor. Based on this focus, the objective of this workwas to characterize the water stress of two maize (Zea mays L.) inbred lines by means ofautomatic sap flow (F) measurements with energy balance probes, installed on segmentsof plants stems. The probes are composed of heating electric resistance (thermal jacket)and registering sensors of heat and temperature flow. The thermal jacket supplied aconstant rate of heat to the stem segment. Thermocouples of copper-constantan wereused as sensors to detect the losses of heat from the thermal jacket to the air surroundingthe stem and the temperature differences in the stem segment studied. The automaticacquisition data system involved a datalogger, sensors, a portable computer, a solar paneland rechargeable batteries. A program was used for readings in the probes sensors andcalculations of the sap flow rates. An equation, expressing the plants water stress index(PWSI) and involving terms of the measured F rates under two water regime conditions(non stressed and stressed), was used in the water stress characterization. The resultsindicated that the probes were sensible to detect variation of sap flow and the PWSI wasan appropriate methodology for water stress characterization of the two maize inbredlines investigated; the total leaf area of the two studied inbred lines was reduced by thewater stress condition; the maize inbred line L 1170 presented smaller values of sap flowand was more sensible (larger values) to the PWSI studied, the maize inbred line L13.1.2 presented larger values of sap flow and was more tolerant to PWSI (smaller values).
