Genotypic variation in root morphology, cotton subtending leaf physiology and fiber quality against nitrogen

Background Nitrogen (N) is important for improving various morphological and physiological processes of cotton but their contribution to fiber quality is still lacking. Aims The current study aimed to explore the relationship between root morphology, subtending leaf physiology, and fiber quality of contrasting N-efficient cotton genotypes in response to N. Methods We analyzed the above parameters of CCRI 69 (N-efficient) and Xinluzao-30 (XLZ-30, N-inefficient) under control (2.5 mmol·L−1) and high N (5 mmol·L−1) conditions. Results The results showed that root morphological traits were increased in CCRI-69 under control conditions than high N. Subtending leaf morphology, chlorophyll and carotenoid contents, free amino acids, and soluble proteins were higher under high N as compared with the control. However, soluble sugars, fructose, sucrose contents, and sucrose phosphate synthase were higher under control conditions than high N across the growth stages. Irrespective of the N conditions, all morphological and physiological traits of cotton subtending leaf were higher in CCRI-69 than XLZ-30. Except for fiber uniformity, fiber quality traits like fiber length, strength, micronaire, and elongation were improved under control conditions than high N. Between the genotypes, CCRI-69 had significantly higher fiber length, strength, micronaire, and elongation as compared with XLZ-30. Strong positive correlations were found between root morphology, soluble sugars, sucrose content, and sucrose phosphate synthase activity with fiber quality traits, respectively. Conclusions These findings suggest that CCRI-69 performed better in terms of growth and fiber quality under relatively low N condition, which will help to reduce fertilizer use, the cost of production, and environmental pollution.