Water stress effects on growth, development, resource capture and resource use efficiency of two contrasting sugarcane genotypes.

High-fibre sugarcane may be suitable for second generation biofuel production in marginal areas.However, quantitative information about its productivity, resource use, efficiency of resource conversion and drought tolerance is lacking.This study compared growth, development and resource capture of two contrasting sugarcane genotypes under well-watered and water stress conditions.A high-sucrose sugarcane cultivar (N19) and a high-fibre sugarcane hybrid (04G0073) were planted in October 2011 at the South African Sugarcane Research Institute rainshelter facility at Mount Edgecombe, Durban, South Africa.All treatments received adequate irrigation for five months.Thereafter, irrigation was withheld from stress treatments while control treatments continued receiving adequate water.This resulted in two periods of water stress for the stress treatments of 21 and 31 days respectively, interspersed by a period of 28 days with adequate soil water brought about through an unintended intrusion of storm water.Green leaf area index (GLAI), stalk growth, radiation interception, relative available soil water content (RASWC) and midday leaf water potential (Ψ L ) were measured regularly.Dry aboveground biomass and its components were measured at harvest.Evapotranspiration was derived from neutron water meter measurements.Water use efficiency (WUE, defined as biomass produced per unit evapotranspiration) and radiation use efficiency (RUE, defined as biomass produced per unit radiation intercepted) were determined at harvest.Under well-watered conditions, 04G0073 grew rapidly, producing 33% more stalks at peak tillering and a higher number of green leaves per stalk, resulting in a 6% higher GLAI than N19.This enabled it to capture 3% and 5% more water and solar radiation, respectively, compared with N19.04G0073 also converted resources more efficiently than N19 (WUE: 7.6 vs. 6.9 kg m -3 ; RUE: 1.52 vs. 1.39 gMJ -1 ) to produce a 12% higher aboveground dry biomass yield.04G0073 partitioned significantly more stalk biomass to fibre (0.58 vs. 0.45) and significantly less to sucrose (0.24 vs. 0.36) than N19.In both genotypes, stalk elongation rates declined when RASWC dropped below 0.55.Stalk elongation of 04G0073 ceased at RASWC=0.3, compared to RASWC=0.4 for N19.Water stress reduced GLAI by 77% and 88% for N19 and 04G0073, respectively, due to decreased green leaf number (4 and 5 leaves) and decreased stalk population (18% and 6%).Water stressed 04G0073 used resources less efficiently than N19 (WUE=5.8 vs. 7.8 kg m -3 ; RUE=0.95 vs. 1.36 g MJ -1 ).This resulted in stressed 04G0073 producing significantly less (23% reduction) aboveground dry biomass than N19.Although 04G0073 used resources more efficiently to produce biomass under well-watered conditions, it was unable to tolerate severe water stress as well as N19 did.The information gathered in this study is useful for calibrating crop models for determining the feasibility of growing high-fibre cane in marginal areas.