Differential Analysis of Endogenous Hormone Levels and Natural Defoliation Traits During Sugarcane ( Saccharum spp.) Maturation

The relationship between natural defoliation rate and endogenous ethylene, indole-3-acetic acid (IAA), and abscisic acid (ABA) levels in four sugarcane cultivars possessing different defoliation traits was investigated. Leaf sheath, leaf scar, and leaf blade samples were collected from the 10th leaf position below the fully expanded leaves during sugarcane maturation stage. Ethylene, IAA, and ABA levels were measured using gas chromatograph, liquid chromatograph, and external standard methods. The results showed that during sugarcane maturation, the highest natural defoliation rate was observed in CYZ03-194, followed by CYZ01-1413, CMT02-467, and CYA99-91. Ethylene production and IAA levels in the leaf scars, leaf sheaths, and leaf blades were the highest during the early-to-mid-maturation stage and decreased afterwards. The ABA levels showed a mono-peak curve change and peaked at the late-to-mid-maturation stage. Ethylene production in leaf scars during the early-to-mid- and mid-maturation stages as well as ABA levels in leaf scars at the late-to-mid-maturation stage significantly differed among the cultivars, with the highest levels in CYZ03-194, followed by CYZ01-1413, CMT02-467, and CYA99-91. On the other hand, the IAA levels in leaf scars and leaf sheaths at the early-to-mid-maturation stage were highest in CYA99-91, followed by CMT02-467, CYZ01-1413, and CYZ03-194. Correlation analysis demonstrated a positive correlation between the natural defoliation rate and ethylene production, ABA level, ethylene/IAA ratios, and ABA/IAA ratios, whereas a negative correlation was observed with IAA level during the early-to-mid- and mid-maturation stages.