Growth and water relations of African marigold under graded moisture regimes and foliar application of melatonin, salicylic acid and GABA

Introduction

African marigold (Tagetes erecta L.) is a commercially important ornamental crop cultivated for looseflower, garden display and pigment production or as coloring agent in poultry feed to obtain yellow egg yolks (Asrar et al., 2011) [1] . Adequate soil moisture is essential for maintaining vegetative growth, leaf expansion, photosynthetic pigments and root development. Moisture deficit can restrict cell expansion and plant growth, disturb tissue water relations and ultimately reduce crop productivity (Kılıc et al., 2024) [2] . Water-saving irrigation practices based on reduced soil moisture availability may help conserve water; however, prolonged moisture deficit can impose considerable physiological limitations on plants. Foliar application of plant growth regulators represents one possible approach for reducing the adverse effects of water deficit. Gamma-aminobutyric acid (GABA), salicylic acid (SA) and melatonin have been reported to participate in stress signalling, osmotic adjustment, antioxidant protection and maintenance of photosynthetic function under abiotic stress conditions (Yong et al., 2017; Basit et al., 2018; Zhang et al., 2022) [4,3,5] . Although these compounds have individually been investigated in different crops, comparative information on their response under graded moisture regimes in African marigold remains limited. Therefore, the present study evaluated the effects of three soil moisture regimes and foliar application of GABA, SA and melatonin on selected growth, pigment, root and water-relation traits of African marigold cv. Pusa Bahar. Relationships among these traits were further examined using correlation and multivariate analyses.

Materials and methods

The pot experiment was conducted during 2024-25 and 2025-26 in Mist chamber of dept. of Floriculture and Landscaping at Rani Lakshmi bai central agricultural university, with African marigold cv. Pusa Bahar. The experiment consisted of three moisture regimes, FC 1 (100% FC), FC 2 (70% FC) and FC 3 (40% FC), and seven foliar sprays: S 0 (water spray, control), S 1 (GABA 200 ppm), S 2 (GABA 400 ppm), S 3 (SA 100 ppm), ISSN Print: 2617-4693 ISSN Online: 2617-4707 NAAS Rating (2026): 5.29 Indexing: Embase S 4 (SA 150 ppm), S 5 (MEL 10 ppm) and S 6 (MEL 20 ppm), giving 21 treatment combinations in three replication. Observations were recorded on chlorophyll a (Cl a , mg/g fresh weight) and b (Cl b , mg/g fresh weight), leaf number (LN; plant -1 ), leaf area (LA; cm 2 ), stem diameter (SD; mm), water saturation deficit (WSD; %), water deficit ratio (WDR), root length (RL; cm), intrinsic water use efficiency (iWUE μmol CO 2 mol -1 H 2 O) and internal water content (IWC, %), root to leaf area ratio (RtoLA). The effects of moisture regime and foliar treatment were evaluated using analysis of variance. Pooled means across the two experimental seasons were used for presentation of the principal treatment effects. Pearson correlation, path analysis, hierarchical clustering and principal component analysis were conducted using treatment means in R software.

Results

Effect of soil moisture regime

Graded Moisture regime significantly influenced the growth, pigment and water-status traits of African marigold (Table 1). Plants maintained at 100% FC recorded the highest chlorophyll a (9.24), chlorophyll b (6.17), leaf number (226.75), leaf area (23.66), stem diameter (8.04), root length (29.92) and internal water content (8.81).

Progressive reduction in soil moisture resulted in a corresponding decline in these traits. At 40% FC, leaf number reduced by 49.6%, leaf area by 46.4%, chlorophyll b by 44.9%, IWC by 45.0%, root length by 39.3%, chlorophyll a by 29.1% and stem diameter by 24.6%. In contrast, WSD and WDR increased with increasing moisture deficit. WSD increased from 11.67 at 100% FC to 38.13 at 40% FC, while WDR increased from 1.36 to 8.43. iWUE increased from 45.47 at 100% FC to 60.78 at 40% FC. The difference in iWUE between 100 and 70% FC was comparatively small.

Effect of foliar treatments

Foliar application generally improved measured growth, pigment concentration and water-status traits relative to the untreated control (Table 2). Among the treatments, melatonin at 20 ppm was the found to be most consistent across several traits. It recorded the highest Chl at (8.94)

Interaction effect of moisture regime and foliar treatments

Interaction effect of morpho-physiological traits under 100%, 70% and 40% FC in African marigold (Tagetes erecta) cv Pusa Bahar. The interaction between moisture regime and foliar treatment was significant for the measured traits except root-to-leaf-area ratio (Fig. 1).

Correlations and multivariate analysis

Pearson correlation analysis revealed two broad groups of associated traits. Growth and pigment traits, including leaf area, Chl a, Chl b, leaf number, root length, stem diameter and IWC, showed strong positive associations with one another (r = 0.83-0.95). In contrast, these traits showed strong negative associations with WSD and WDR (r = -0.80 to -0.94). WSD and WDR were themselves strongly positively associated (r = 0.95). IWUE showed relatively weak associations with most of the measured traits (r = -0.15 to 0.42), indicating that its response to moisture deficit was not directly aligned with the major growth variables. Root-to-leaf-area ratio showed negative associations with leaf area and stem diameter.

Principal component analysis showed that PC1 and PC2 explained 77.9 and 9.8% of the total variation, respectively, accounting for 87.7% of the overall variation. PC1 primarily separated well-watered treatments from the 40% FC treatments based on the contrasting distribution of growth/pigment traits and water-deficit indicators. iWUE and root-to-leaf-area ratio contributed more strongly to PC2.

Hierarchical clustering produced a similar pattern. Most well-watered treatments and sprayed 70% FC treatments were grouped together, whereas the 40% FC treatments formed a separate group. The un-treated severe-stress treatment, FC 3 S0, was the most distinct treatment in the multivariate analysis.

Discussion

The steady decline in leaf number, leaf area, chlorophyll and root length with decreasing moisture reflects the well-known suppression of cell expansion, pigment synthesis and root proliferation under water deficit (Abd El-Gawad et al., 2021; Kılıc et al., 2024) [6,2] . The decline in chlorophyll concentration further indicates impairment of pigment maintenance under severe moisture deficit (Tavassoli et al., 2025) [7] . The increase in WSD and WDR together with the decline in IWC at 40% FC indicate unstable tissue hydration, and the strong negative correlations of these traits with growth traits further indicates that deterioration in plant water status was closely associated with reductions in vegetative growth. A increase in WSD could lead may be due severity of drought which can lead to a decrease in leaf water content, cell turgor pressure, potentially impacting the plant's strength and structural integrity (Liu et al., 2022; Kumar et al., 2018) [9,8] . The interaction data show that iWUE was lowest in unsprayed severely stressed plants (34.1) and nearly doubled with sprays (64.0-66.7), suggesting that the bioregulators helped plants retain intrinsic water-use efficiency under severe stress. This agrees with the weak correlation of IWUE with the other traits and its separate loading on PC2. The positive response to foliar application is consistent with the known stress-related functions of GABA, SA and melatonin. GABA accumulates under stress and contributes to osmotic adjustment, membrane stabilisation and antioxidant defence (Yong et al., 2017; Abd El-Gawad et al., 2021) [4,6] . SA acts as a signalling molecule under stress and can influence growth and physiological processes under adverse environmental conditions (Basit et al., 2018) [3] , which may explain the higher leaf area and IWUE at 100 ppm. Melatonin reduces oxidative damage and helps retain chlorophyll and tissue water under drought (Silalert et al., 2021; Zhang et al., 2022) [10,5] . The absence of a benefit from higher GABA and SA doses suggests that the response saturates at moderate concentrations, a common pattern with growth regulators. The clustering of the sprayed 70% FC plants with the well-watered group, and of the unsprayed 70% FC plants with the 40% FC group, indicates that foliar treatment can compensate for a 30% reduction in available moisture. At 40% FC, however, sprays reduced but did not completely remove the effects of severe moisture deficit. The present findings therefore suggest that foliar bioregulators can moderate the adverse effects of reduced soil moisture in African marigold, with the magnitude of response depending on both the moisture regime and the compound applied.

Conclusion

Reducing soil moisture from 100 to 40% FC substantially affected growth, pigment accumulation, root development and tissue water status of African marigold cv. Pusa Bahar. Leaf number, leaf area, chlorophyll concentration, root length and internal water content declined progressively with increasing moisture deficit, whereas water saturation deficit and water deficit ratio increased. Foliar application of GABA, SA and melatonin partially alleviated these effects. Among the tested treatments, melatonin at 20 ppm showed the most consistent improvement across several growth, pigment and water-status traits, while SA at 100 ppm produced the highest leaf area and IWUE and GABA at 200 ppm produced the highest stem diameter. Under 70% FC, several sprayed treatments showed responses comparable with well-watered plants for selected traits, whereas severe moisture deficit at 40% FC continued to impose a substantial growth penalty even after foliar treatment. Overall, the findings indicate that foliar application of GABA, SA and melatonin can contribute to maintaining growth and water status of African marigold under reduced soil moisture, with melatonin at 20 ppm showing particularly consistent effects across the traits evaluated in the present study.

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12. How to cite this article: Tiwari S, Sharma G, Sharma P, Shrivastav A, Singh A, Abrol G, et al. Growth and water relations of African marigold under graded moisture regimes and foliar application of melatonin, salicylic acid and GABA. International Journal of Advanced Biochemistry Research. 2026;SP-10(10):443-447. doi: https://www.doi.org/10.33545/261 74693.2026.v10.i10Sf.10319