Exogenous Application of Ethrel and Gibberellic Acid Stimulates Physiological Growth of Late Planted Sugarcane with Short Growth Period in Sub-tropical India

Physiological growth of late planted sugarcane crop is restricted by high temperature and a short growth period. This causes considerable reduction in crop and sucrose yields. Improving physiological growth within the short period is, therefore, highly desirable. Two field experiments were undertaken to determine the effect of exogenous applications of Ethrel and gibberellic acid (GA₃) on sprouting, shoot population and physiological growth. Sugarcane setts were soaked overnight in Ethrel before planting. Foliar application of GA₃ was performed at 90, 120 and 150 days after planting (DAP). Ethrel soaking led to 100% sprouting and high settling population at 20 DAP, due to a significant increase in bud moisture and activities of acid invertase (AI), indole acetic acid oxidase (IAAO), adenosine triphosphatase (ATPase), superoxide dismutase (SOD) and nitrate reductase (NR) activity in vivo. Early sprouting increased the growth period to 245 days compared to 220 days in the unsoaked setts. The applications increased leaf area (57%), leaf area index (76%), leaf area ratio (71%), leaf area duration (48%), biomass duration (52%) and net assimilation rate (69.64%) at the grand growth stage. The changes led to increased shoot numbers (26.3%), internodal numbers stalk⁻¹ (40.74%), internodal length (40%), internodal girth (46.15%) and stalk length (42%) at the harvest stage. The stimulated physiological growth augmented dry matter content, ᵒBrix and purity of cane juice by 24.2, 3 and 0.3%, respectively. The study demonstrates that the induction of higher shoot numbers together with increased leaf area index (LAI) and stalk elongation within a short growth period through Ethrel soaking and gibberellic acid applications is positively associated with enhanced dry matter and sucrose contents.