Biochemical responses of Robusta coffee to water deficit conditions

Abstract

Drought stress poses a major challenge to crop productivity by altering the biochemical composition, antioxidant defenses, and morphological development. This study investigated how the biochemical responses and the antioxidant system in Robusta coffee relate to the morphological traits under water deficit conditions. Rooted cuttings of seven CWD-r Robusta coffee varieties (KR1-KR7) were evaluated under four watering regimes (100%, 75%, 50%, and 25% field capacity, FC) in a split-split plot randomized complete block design over two temperature environments, low (LTS) and high (HTS). Morphological parameters (plant height, leaf blade length, leaf blade width, stem internode length, number of stem nodes, and number of stem internodes) were measured fortnightly for four months. Fourier transform infrared spectroscopy was used to quantify key biomolecules (carbohydrates, lipids, and proteins) from the leaves, while the 2,2-diphenyl-1-picrylhydrazyl assay was used to assess total antioxidant activity and capacity monthly for four months. Findings demonstrated significant interactive effects of temperature, moisture regime, and variety on the biochemical profile, of CWD-r Robusta coffee varieties. However, under severe drought stress, this coordination weakens as antioxidants become decoupled from biochemical maintenance, particularly under high temperatures. KR5 consistently maintained the highest biomolecule accumulation across most regimes, while KR2 and KR4 had lower biomolecule reserves under stress. TAA and TAC were stable across varieties but peaked for variety KR6 under mild (75% FC) and moderate (50% FC) moisture stress, highlighting the role of antioxidants in stress mitigation. Correlation analyses revealed robust positive associations among the spectral regions corresponding to the biomolecules, confirming a coordinated response to drought stress. Correlations between the biochemical markers and morphological parameters (such as plant height, stem node/internode counts, and leaf dimensions) were weak to moderate, suggesting that while metabolic adjustments are integral for stress mitigation, the morphological outcomes are governed by a more complex interplay of factors. A multi-trait genotype-ideotype distance index was applied to rank variety performance under distinct stress scenarios. Under well-watered (100% FC) and mild water stress (75% FC), KR1 emerged as the most promising genotype. Under moderate water deficit (50% FC), KR7 and KR3 were identified as the most suitable varieties in the HTS and LTS, respectively. Under 25% FC, KR1 and KR5 showed the strongest combination of biochemical accumulation and antioxidant defenses in the HTS and LTS respectively securing their ranking as the most water stress resilient varieties.