Studies on the effect of bioinoculants, plant growth regulators and humic acid on growth and flower yield of African marigold (Tagetes erecta) under walk-in tunnel

Introduction

Marigold (Tagetes spp.) is gaining prominence as a commercially valuable floricultural crop in India, primarily due to its ease of cultivation, adaptability, and increasing market demand. This genus, belonging to the Asteraceae (or Composite) family, encompasses approximately 33 species. Commercially, marigolds are integral to the pigment extraction industry and dried flower production, serving as a natural source of carotenoids such as xanthophyll and lutein (C40H56O2), oleoresins, and natural dyes. The aromatic oil derived from marigold flowers, known as "tagetes oil," finds application in the creation of high-quality perfumes and in pharmaceutical formulations. Furthermore, dried marigold petals are incorporated into poultry feed as natural food additives to enhance the pigmentation of egg yolks and broiler skin, while simultaneously boosting their vitamin A content. Biofertilizers have proven to be an excellent source of essential nutrients for plants, while also enhancing soil fertility and improving soil structure. They offer a sustainable and practical solution for producing high-quality flowers and achieving greater yields on a commercial scale. Moreover, biofertilizers are environmentally friendly, readily accessible, and economically viable, making them an ideal choice for profitable floriculture. External application of growth regulators significantly boosts flower production by directing a greater allocation of nutrients towards the reproductive organs of the plant. Among the most critical growth regulators for African marigold are Gibberellic Acid (GA3) and Naphthalene acetic Acid (NAA). These compounds are known to promote vigorous growth, enhance flower yield, and precisely control plant development and flowering. Additionally, Humic acid facilitates ion uptake and encourages the growth of lateral roots.

Methods and Materials

The experiment was conducted at the Centre of Excellence for Protected Cultivation and Precision Farming, located at the College of Agriculture, Indira Gandhi Krishi Vishwavidyalaya, Raipur (C.G.), during the Rabi season of 2024-25. The experiment was laid out in factorial randomized block design with 3 replications and 15 treatments viz T

Results and Discussion

Number of days to 50% flowering Among soil applied bioinoculants, the minimum number of days to 50% bud initiation (37.81 days) was recorded under the treatment (SD1) PSB @10%, which was significantly earlier than all other treatments. This was followed by (SD2) KSB @10% (45.22 days) and among foliar applied bioinoculants (36.52 days) was recorded under the treatment (FS2) GA₃ @200 ppm, which was significantly earlier than all other treatments. This was followed by (FS3) NAA @50 ppm (45.44 days) and (FS1) 0.2% Humic acid (45.96 days). Among different treatment combinations minimum number of days to 50% bud initiation (33.69 days) was recorded under the treatment T 7 (SD2 -PSB @10% + FS2 -GA₃ @200 ppm), which was significantly earlier than all other treatments. This was followed by T 6 (SD1 -PSB @10% + FS1 -0.2% Humic acid) with 36.89 days and T 11 (SD2 -KSB @10% + FS2 -GA₃ @200 ppm) with 37.46 days. Similar findings were also reported by Yadav et al. (2013) [1] , Kumar et al. (2022) [2] , and Megha et al. (2022) [3] .

Number of days to full bloom

Among soil applied bioinoculants, the minimum number of days to 100% flowering (49.67 days) was recorded under the treatment (SD1) PSB @10%, which was significantly earlier than all other treatments. This was followed by (SD2) KSB @10%, which recorded 59.64 days to full bloom and among foliar applied bioinoculants (49.28 days) was recorded under the treatment (FS2) GA₃ @200 ppm, which was significantly earlier than all other treatments. This was followed by (FS3) NAA @50 ppm, which recorded 57.63 days to full bloom. Among different treatment combinations, minimum number of days to 50% flowering (45.90 days) was recorded under treatment T 7 (SD1 -PSB @10% + FS2 -GA₃ @200 ppm), which was significantly earlier than all other treatments. This was followed by T 6 (SD1 -PSB @10% + FS1 -0.2% Humic acid) with 48.28 days. Similar findings were reported by Himabindu (2010) [4] , Shaikh et al. (2018) [5] .

Among soil applied bioinoculants, the maximum flower diameter (4.79 cm) was recorded under the treatment SD₂ (KSB), which was significantly superior to all other treatments. and among foliar applied bioinoculants (4.75 cm) was recorded under FS2 (GA₃ 200 ppm). Among different treatment combinations, the maximum flower diameter bioinoculants (4.98 cm) was recorded under T 11 (SD2 (KSB) @10% +FS2 (GA3 200ppm)), which was statistically superior to all other treatments. This was followed by T 10 (SD2 (KSB) @10% +FS1 (0.2% Humic acid)) (4.89 cm). Similar findings were reported by Yadav et al. (2018) [15] and Kumar & Kumar (2017) [6] in marigold.

Flower yield per hectare (q/ha) Among soil applied bioinoculants, the maximum flower yield per hectare (117.32 q/ha) was recorded under the treatment SD₂ (KSB) and (116.42 q/ha) was recorded under the treatment FS₂ (GA₃ @ 200 ppm). Among different treatment combinations, the maximum flower yield per hectare (119.90 q/ha) was recorded under the treatment T 7 (SD1 + FS2: PSB @10% + GA₃ 200 ppm). Similar findings have been reported by Verma and Arha (2004) [9] and Palagani et al. (2013) [10] in chrysanthemum, Singh and Kumar (2016) [11] and Kumar & Kumar (2017) [6] in marigold, and Jogi et al. (2022) [12] in China aster.

Fresh weight of flowers per plant (g) Among soil applied bioinoculants, the maximum average fresh weight of flowers per plant (304.50 g) was recorded with SD2 (KSB @10%) and among foliar applied bioinoculant (324.84 g) was recorded with FS2 (GA₃ 200 ppm), which was significantly higher than all other treatments. Among different treatment combinations, the maximum average fresh weight of flowers per plant (368.20 g) was recorded under the treatment combination T 11 (SD2 [KSB @10%] + FS2 [GA₃ 200 ppm]), which was significantly superior to all other treatments. It was followed by T 7 (SD1 [PSB @10%] + FS2 [GA₃ 200 ppm]) (323.88 g). Similar findings were reported by Kumar et al. (2022) [2] in China aster, Singh and Kumar (2016) [11] in marigold, Jogi et al. (2022) in China aster, and Kumar and Kumar (2017) [6] in marigold.

Among soil applied bioinoculants, the maximum average dry weight of flowers per plant SD2 (KSB10%) (86.59 g), which was statistically at par with SD1 (PSB10%) (84.97 g) and among foliar applied bioinoculants (91.96 g) was recorded under FS2 (GA₃ 200 ppm), which was significantly superior to all other treatments. This was followed by FS1 (0.2% humic acid) with 71.67 g and FS3 (NAA 50 ppm) with 68.41 g. Among different treatment combinations, the maximum average dry weight of flowers per plant (103.03 g) was recorded under the treatment combination SD2 (KSB @10%) + FS2 (GA₃ 200 ppm) (T 11 ), which was statistically at par with SD1 (PSB @10%) + FS2 (GA₃ 200 ppm) (T 7 , 99.97 g). Similar findings were reported by Likhitha et al. (2024) [13] , Kumar and Kumar (2017) [6] in marigold, Pansuriya et al. (2018) [7] in gladiolus, and Patil and Agasmani (2013) [8] in China aster.

Flowering span

Among soil applied bio inoculant, maximum flowering duration was observed under (75.71 days) in plants treated with SD1 (PSB @10%) and among foliar applied bioinoculants (81.37 days) was recorded in plants treated with FS2 (GA₃ 200 ppm). Among treatment combinations Maximum flowering duration (82.29 days) was recorded under treatment T 7 [SD1 (PSB @10%) + FS2 (GA₃ 200 ppm)], which was statistically at par with T 11 [SD2 (KSB @10%) + FS2 (GA₃ 200 ppm)] (82.11 days).

Among soil applied bioinoculants, maximum shelf life was observed in the application of soil drenching of (3.50 days) SD0 (No soil drenching), which was significantly higher than all other treatments and (3.75 days) was observed with the foliar application of FS1 (0.2% Humic acid), which was significantly superior to the rest of the treatments. Maximum shelf life was observed in treatment combination of (5.42 days) T 2: SD0 + FS1 (0.2% Humic acid), significantly superior to all other treatments. Next best was T 7: SD1 + FS2 (GA₃) (3.64 days), T 3: SD0 + FS2 (GA₃) (3.62 days) as also reported by Goyal and Singh (2023) [14] in petunia.

Conclusion

The results indicating the effect of soil applied bioinoculants and foliar applied plant growth regulators and humic acid on flower yield, quality and shelf life in African marigold revealed that soil drenching of PSB@10% alone and foliar application GA3 200ppm. Treatment combination T 7 (SD1(PSB) @10% +FS2 (GA3 200ppm)) and T 11 (SD2(KSB) @10% +FS2(GA3200ppm)) performed best with regards to early 50% flowering, minimum number of days to full bloom, flower yield per hectare, flower diameter, fresh weight of flowers per plant, dry weight of flowers per plant, flowering span and shelf life in African marigold.

References

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