Abstract:
The study was conducted to evaluate some physiological characters of commercial sugarcane varieties
under different growing conditions in Sri Lanka. A field experiment was conducted at the Sugarcane
Research Institute, Uda Walawe (6o21’N latitude, 80o 48’E longitude and 76 m altitude) using eight sug arcane (Saccharum hybrid L.) varieties grown under irrigated and rainfed conditions in a split plot de sign. Stomatal conductance (gs), instantaneous transpiration rate (E1) and photosynthetic rate per unit
leaf area (Pn) were measured. Canopy stomatal conductance (gc), instantaneous canopy transpiration
rate (Ec) and transpiration efficiency (Pn/E1) was calculated. The behaviour of gs in many respects to the
moisture availability and growing stage was similar to the responses seen in Pn. Water deficit significantly reduced gs, E1 and Pn. Recovery of gs and Pn from water stress with rainfall was quite rapid un der rainfed conditions. The varieties Co775, SL8306, SL7103 and SL88116 which had higher Pn and Pn/
E1, and lower gs, E1, gc and Ec showed comparatively superior physiological performances under rainfed
conditions. Water conservation through lowering stomatal conductance, both at the individual leaf and
canopy level, and higher photosynthetic rate were identified as some physiological mechanisms respon sible for drought tolerance of sugarcane.
