Analysis of toxic and osmotic effects of sodium chloride on leaf growth and economic yield of sugarcane

Sugarcane (Saccharum officinarum L.) an important sugar crop, shows high sensitivity to salinity at various growth stages. This study was conducted to determine the comparative response of a salt-tolerant (CP-4333) and a salt-sensitive (CP-71-3002) sugarcane clone to the toxic or osmotic effects of sodium chloride at two growth stages. Clones indicated significant differences in terms of reductions in dry weight and area of leaves under salinity at the grand growth stage. Leaf dry weight was more affected than leaf area, resulting in reduced specific leaf weight. The tolerant clone produced supplementary tillers in greater number that appeared to offload the ion excess. Clones indicated significant difference with regard to increase in leaf Na and Cl and decrease in K, but no difference in K: Na ratio. Na and Cl were negatively correlated while K was positively correlated with leaf growth parameters, indicating an adverse effect of Na and Cl and importance of K to salt tolerance. The tolerant clone displayed higher water content, water, and turgor potentials of leaf than sensitive clone, but the osmotic potential did not significantly change. Soluble sugars of tolerant clone indicated a ~2 fold increase over control, indicating their osmo-protective role. Free proline accumulation was more specific to the sensitive clone and was correlated with Na and Cl showing its synthesis due to ion-toxicity. At maturity, increased salinity reduced the millable cane yield, extractable juice and juice-brix percentage, but increased juice osmolality. All these parameters were negatively correlated with EC, Na, and Cl and displayed their specific effect on the sugar levels in the internodes. In summary, ion-toxicity was the main determinant of salt tolerance at the grand growth stage while the osmotic component of NaCl mainly appeared to affect the transport of sucrose to stalks, followed by stimulated sucrolytic activity in the internodes, resulting in reduced final cane yield.