The reaction of sugarcane to water stress
Inman-Bamber, Neville Geoffrey
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The effects of water stress on plant water relations, growth, water use and sucrose accumulation were investigated with the aid rainshelters. In the first experiment various aspects of the water status of cane growing in large pots were measured. The pots were weighed to determine water use. In the second experiment similar measurements were made on cane grown in the field. Crop growth was measured non-destructively and water use was determined with a neutron probe. The threshold leaf water potentials for various attributes were determined as follows: 1) at -0.2 MPa, plant extension rate fell below potential, 2) at -0.3 MPa, stomatal resistance started to increase, 3) at -0.4 to -0.9 MPa plant extension ceased, 4) at -0.8 MPa, leaves started to roll, 5) at -1.0 to -1.7 MPa, green leaf area was reduced, 6) at -1.2 to -1.7 MPa, stomatal resistance rose rapidly, 7) at -1.4 to -2.3 MPa, stomata finally closed, 8) at -2.0 MPa, young leaves were fully rolled and 9) at -2.8 MPa, the apical meristem was permanently damaged. Osmotic adjustments during stress were reversed when plants recovered and there was no evidence of osmotic hardening. Stomata became more, rather than less sensitive to stress after a stress period in the field. The drought resistance of N12 was evidently due to its relatively low stress threshold for stomatal closure. This behaviour of stomata distinguished the species as one that avoids rather than endures drought. A crop water stress index (CWSI) based on infra-red thermometry correlated reasonably well with plant extension rate, leaf water potential and canopy resistance. Crop growth potential and water use efficiency appeared to vary considerably through the year. Cane yield increased by more than 1',0t had -1 during the hottest months,Water stres sappeared to have no permanent effect on cane growth rate provided stalk death did not result from stress. Water stress promoted ripening when plant extension was reduced and before stomata finally closed. Sucrose was apparently not readily removed from the lower inter-nodes to support new growth when water stress was relieved.