Fortification with micronutrients and plant growth regulators improves the vegetative and reproductive parameters of bananan cv. Popoulu (AAB)

Introduction

Banana (Musa spp.) is an herbaceous, perennial monocotyledonous plant belonging to the family Musaceae and order Scitamineae with the chromosome number X=11 and origin South East Asia. It is most widely cultivated and consumed fruit in India, with a long history of cultivation dating back to prehistoric times. The term "banana" originated from West Africa and was introduced by the Portuguese, while "plantain," referring to cooking types, comes from the Spanish plantano (Purseglove, 1975) [27] .

Bananas are mainly eaten as dessert fruits, whereas starchier plantains are used for cooking and form an essential dietary component in Africa, the Caribbean and Latin America. Ripe bananas are nutritious, energy-rich and easily digestible (Aurore et al., 2009) [5] . Globally, banana ranks fourth after rice, wheat and maize in production value. It serves as both a staple and dessert fruit, rich in easily digestible carbohydrates (67-137 k cal/100 g) and a good source of vitamins A, C, B₁ and B₂ (Premalatha and Suresh, 2019) [25] .

In India, banana is second most important crop next to mango. The global production of banana is around 139.6 million tonnes. In India, present area is 9.95 lakh ha and production is 374.74 lakh tonnes. In Karnataka, it is cultivated in 1.71 lakh ha area with the production of 29.13 lakh tonnes (Anon., 2023) [1] . In Karnataka, major banana cultivars include Dwarf Cavendish, Robusta, Rasthali, Poovan, Nendran and Red Banana. Among these, Nendran is the leading commercial cultivar for chips preparation, highly preferred by both consumers and processors. However, Nendran has low yield potential (10-12 kg/plant). To address this, "Popoulu," an AAB group cultivar from the Pacific Islands, was introduced by NBPGR, New Delhi, from the Musa International Transit Centre, Belgium and evaluated at the Banana Research Station, Kannara, Kerala (Menon et al., 2014) [20] . Popoulu is a cooking banana cultivar growing 2-3 m tall with a sturdy pseudostem and large, green, paddle-shaped leaves. Its fruits are short, thick and angular, suitable for chips preparation with 33% recovery, comparable to cv. Nendran and it can also be used as a dessert fruit (Manju and Pushpalatha, 2022) [19] . Plant growth, yield and fruit quality are all significantly impacted by balanced nutrition. The banana is an exhaustive crop that needs a sufficient amount of nutrients to support its robust growth, high yield and biomass production throughout its growth cycle. Micronutrients are essential for the crop growth and are equally important as primary and secondary nutrients. They have an important role in the balance of plant nutrition for the stabilization of crop yield and quality of produce. Though these micronutrients are necessary in very small amounts, but are essential for controlling plant development and fostering physiological reactions in them. Because of the limited nutrient absorption through the root system, foliar application of micronutrients has been successfully used to improve flowering, synchronize blooming, enhance fruit size through cell division, which ultimately increases the yield. Plant growth regulators (PGRs) are natural hormones that influence plant physiological processes by stimulating enzymes that control metabolism. They promote cell division, elongation, differentiation, root growth, shoot growth, flowering, fruiting and are used to enhance yield and reduce stress (Rajan et al., 2017) [28] . Since Popoulu variety possesses superior yield and quality parameters compared to Nendran variety and because of its increasing demand in processing industries, there is a need to increase its quality production. Therefore, the present study aims to investigate the effect of micronutrients and plant growth regulators on vegetative and reproductive characteristics of banana cv. Popoulu (AAB).

Material and methods

This experiment was carried out at ICAR-All India Coordinated Research Project on Fruits, located at Kittur Rani Channamma College of Horticulture, Arabhavi, Belagavi district of Karnataka, India during the year 2024-2025. The experiment laid out in Randomized Complete Block Design with ten treatments and three replications. The spacing used here was 1.8 x 1.8 m. The treatment combination are as follows, T1 (ICAR-IIHR Banana special @ 0.5%), T2 (ICAR-NRCB Banana shakthi powder @ 1%), T3 (Sampoorna KAU multimix @ 1%), T4 (ICAR-IIHR Banana special @ 0.5% + CPPU 4 ppm), T5 (ICAR-NRCB Banana shakthi powder @ 1% + CPPU 4 ppm), T6 (Sampoorna KAU multimix @ 1% + CPPU 4 ppm), T7 (ICAR-IIHR Banana special @ 0.5% + GA3 80 ppm), T8 (ICAR-NRCB Banana shakthi powder @ 1% + GA3 80 ppm), T9 (Sampoorna KAU multimix @ 1% + GA3 80 ppm) and T10 (Control -water spray) sprayed at 6 th , 7 th , 8 th , 9 th and 10 th month after planting. The recommended dose of fertilizer followed in the experiment was 200:100:300 g NPK/plant/year, as per the Package of Practice of UHS, Bagalkot, Karnataka and was applied uniformly to all treatments. The 5 g IIHR banana special, 10 g of each NRCB Banana shakthi and Sampoorna KAU multimix were accurately measured and dissolved in one litre of water seperately. Similarly, 0.04 ml of CPPU and 0.08 g of progib (GA3) were measured. The required concentrations of micronutrients and plant growth regulators were prepared by directly mixing the respective quantities in water and freshly prepared solutions were used for spraying during 6 th , 7 th , 8 th , 9 th and 10 th month after planting using knapsack power sprayer. Observations were recorded for various growth parameters such as pseudostem height, measured from the soil surface to the base of the leaf-emerging point using a measuring tape; pseudostem girth, measured from 15 cm above the ground using a measuring tape; number of functionally active leaves, were manually counted; leaf area, determined by multiplying leaf length, breadth and the number of leaves with a constant factor of 0.80, as per Murray's method (1960); Chlorophyll content in leaves was measured using a SPAD meter, number of suckers per plant were counted manually before their removal and recorded at 6 th and 7 th months after planting. Reproductive parameters such as number of days taken for shooting, number of days taken from shooting to maturity, total crop duration and bunch weight were documented. The obtained data were statistically analyzed in a randomized complete block design (RCBD) by using analysis of variance by Fisher and Yates (1963). When F-test showed significance in comparing treatment means, critical differences (C.D. at 5%) were calculated.

Results and Discussion

The data on pseudostem height and girth of banana cv. Popoulu was significantly influenced by foliar application of micronutrients and plant growth regulators. Among the different treatments, the maximum pseudostem height (263.19 and 293.34 cm) and greatest pseudostem girth (82.41 and 85.55 cm) were recorded in T8 (ICAR-NRCB Banana shakthi powder @ 1 per cent + GA3 @ 80 ppm applied at 6 th , 7 th , 8 th , 9 th and 10 th MAP). Whereas, the minimum pseudostem height (204.50 and 225.50 cm) and lowest pseudostem girth (55.00 and 58.64 cm) were registered in T10 (control) at 6 th and 7 th MAP, respectively. The increase in pseudostem height and girth might be due to the foliar application of micronutrients that enhance cell enlargement and metabolic activity with zinc promoting auxin production, copper aiding enzyme activation and chlorophyll formation (Ram and Bose, 2000) [29] , resulting in vigorous pseudostem growth. These findings were well supported by Kumar and Jeyakumar (2001) [17] in cv. Robusta, Yadlod and Kadam (2003) [35] in banana cv. Grand Naine, Rashid and Mondal (2007) [30] in banana cv. Amritsagar, Jeyabaskaran and Pandey (2008) [14] in cv. Karpuravalli, Bashma et al. (2018) [8] in cv. Nendran, Nisarga et al. (2022) [23] in banana cv. Rajapuri, Arthi and Shakila (2023) [4] in banana cv. Red Banana and Balaji et al. (2023) [6] in banana cv. Poovan. Enhanced pseudostem height and girth could be attributed to the application of GA₃ which stimulates the physiological processes that promote cell division, elongation and cambial activity, resulting in greater vascular development, efficient nutrient transport and overall pseudostem thickening and elongation. The similar observations were noticed by Yadlod and Kadam (2008) [36] in banana cv. Ardhapuri. Fathi et al. (2011) [11] in persimmon cv. Costata, Muralidhara et al. (2014) [21] in seedlings of mango var. Bappakkai, Singh et al. (2018) [31] in Papaya cv. Pusa Nanha and Kanwar et al. (2024) [15] in citrus cv. Nagpur mandarin.

Number of functional leaves (no.)

Admist all different treatments, the maximum number of functionally active leaves (16.47 and 18.36) were documented in T8 (ICAR-NRCB Banana shakthi powder @ 1 per cent + GA3 @ 80 ppm at 6 th , 7 th , 8 th , 9 th and 10 th MAP). Whereas, the least number of functional leaves (11.49 and 12.07) at 6 th and 7 th MAP, respectively were recorded in T10 (control). The application of micronutrient mixture, which optimize the availability of essential trace elements that serves as cofactors in enzymatic and metabolic pathways, that facilitates the chlorophyll biosynthesis and maintain higher photosynthetic rates resulting in increased number of functionally active leaves. These results are in agreement in banana with Kumar and Jeyakumar (2001) [17] in cv. Robusta, Rashid and Mondal (2007) [30] in cv. Amritsagar, Jeyabaskaran and Pandey (2008) [14] in cv. Karpuravalli, Yadav et al. (2010) [34] cv. Grand Naine, Pathak et al. (2011) [24] in cv. Marthaman, Krishnamoorthy and Noorjahan (2017) [16] in cv. Poovan, Bashma et al. (2018) [8] in cv. Nendran, Premalatha et al. (2020) [26] in cv. Nendran, Nisarga et al. 2022 [23] in banana cv. Rajapuri, Arthi and Shakila (2023) [4] in cv. Red Banana and Balaji et al. (2023) [6] in cv. Poovan. GA₃ might accelerate meristematic activity and leaf primordia development, increasing the rate of leaf emergence and overall leaf count. The above results were found parallel with findings of Yadlod and Kadam (2008) [36] in banana cv. Ardhapuri, Bhat et al. (2011) [9] in grape vines of cv. Tas-A-Ganesh, Fathi et al. (2011) [11] in persimmon cv. Costata, Kumar et al. (2012) [18] in strawberries and Singh et al. (2018) [31] in Papaya cv. Pusa Nanha.

The treatment T8 (ICAR-NRCB Banana shakthi powder @ 1 per cent + GA3 @ 80 ppm at 6 th , 7 th , 8 th , 9 th and 10 th MAP) recorded the highest leaf area (12.73 and 16.34 m²) at the 6 th and 7 th MAP, respectively, while the lowest leaf area (8.00 and 10.93 m²) was registered in T10 (control) at the corresponding stages. The application of micronutrients contributes to the production of essential auxins, which promote cell division and chlorophyll synthesis, leading to enhanced leaf enlargement. In addition, micronutrients improve photosynthetic efficiency and facilitate protein synthesis, thereby increasing the total leaf area. Similar findings were reported by Jeyabaskaran and Pandey (2008) [14] in cv. Karpuravalli, Yadav et al. (2010) [34] in cv. Grand Naine, Krishnamoorthy and Noorjahan (2017) [16] in cv. Poovan, Bashma et al. (2018) [8] in cv. Nendran, Arthi and Shakila (2023) [4] in cv. Red Banana, and Nisarga et al. (2022) [23] in cv. Rajapuri. In addition to this GA3 also enhances phloem loading and transport of assimilates and minerals to developing leaves, supporting rapid lamina expansion as suggested by Bhat et al. (2011) [9] in grape vines of cv. Tas-A-Ganesh.

Chlorophyll content (SPAD units)

Among the treatments, T8 (ICAR-NRCB Banana shakthi powder @ 1 per cent along with GA3 @ 80 ppm applied at 6 th , 7 th , 8 th , 9 th and 10 th MAP) recorded the highest chlorophyll levels, with values (44.33 and 49.98 SPAD units). On the other hand, the lowest (35.20 and 36.83 SPAD units) at 6 th and 7 th MAP, respectively. The increase in chlorophyll content may be due to magnesium's role in chlorophyll formation and involvement of micronutrients like iron, zinc, manganese and copper as cofactors in chlorophyll biosynthesis and photosynthesis, thereby enhancing chloroplast development and reducing chlorophyll degradation. These results are in line with Kumar and Jeyakumar (2001) [17] in cv. Robusta and Jayachandran et al. (2005) in guava cv. Lucknow-49. GA₃ treatment may increase chlorophyll content by enhancing chlorophyll-synthesizing enzymes and delaying leaf senescence. This finding is supported by Fathi et al. (2011) [11] in persimmon cv. Costata.

Number of suckers (no.)

The treatment T8 (ICAR-NRCB Banana shakthi powder @ 1 per cent combined with GA3 @ 80 ppm at 6 th , 7 th , 8 th , 9 th and 10 th MAP) resulted in the highest number of suckers, recording (9.80 and 11.03) at 6 th and 7 th MAP, respectively. The least number of suckers (4.63 and 5.03) were recorded in T10 (control) at the corresponding stages.

Foliar application of micronutrients at appropriate crop growth stages enhances their uptake and physiological use, thereby stimulating vigorous growth and promoting increased sucker initiation which is similar with the findings of Pathak et al. (2011) [24] in cv. Martaman and Anu Shetty et al. (2022) [3] in cv. Rajapuri. The positive influence of GA3 on sucker production could be attributed due to its ability to enhance overall plant growth, which in turn improve nutrient uptake efficiency and thereby promote initiation and development of more suckers (Swennen et al., 1984) [33] in plantain.

Reproductive parameters

Among all the treatments, T8 (ICAR-NRCB Banana shakthi powder @ 1 per cent combined with GA3 @ 80 ppm at 6 th , 7 th , 8 th , 9 th and 10 th MAP) showcased early shooting (209.59 days), early maturity (68.92 days) and a shorter crop duration of (278.51 days) which was lesser than other treatments. However, T10 (control) exhibited delayed shooting (230.82 days), late maturity (95.04 days) and a longer crop duration (325.86 days). Crop duration is an important factor to be considered in banana cultivation. In the present experiment, it was recorded that the use of micronutrients and plant growth regulators resulted in early floral bud differentiation, due to optimum vegetative growth, which in turn led to early shooting. Similar findings were reported by Balakrishnan and Rajangam (2002) [7] in cv. Red banana, Yadlod and Kadam (2003) [35] in cv. Grand Naine, Rashid and Mondal (2007) [30] in cv. Amritsagar, Yadav et al. (2010) [34] in cv. Grand Naine, Pathak et al. (2011) [24] in cv. Martaman, Krishnamoorthy and Noorjahan (2017) [16] in banana cv. Poovan, Anu Shetty et al. (2022) [3] in cv. Rajapuri and Nisarga et al. (2022) [23] in cv. Rajapuri.

Application of GA3 might delay the leaf senescence and maintain higher chlorophyll content, improving nutrient mobilization and sustain photosynthetic efficiency to accelerate floral initiation and fruit development, resulting in early shooting, maturity and reduced crop duration as found in banana by Anilkumar and Brahmachari (2006) [2] in var. Harichal, Ebeed et al. (2008) [10] cv. Grand Naine and earliest flowering was observed in guava cv. Allahabad Safeda (Suman et al., 2021) [32] .

Conclusion

The present study revealed that foliar application of ICAR-NRCB Banana Shakthi powder @ 1% + GA₃ @ 80 ppm applied at 6 th , 7 th , 8 th , 9 th and 10 th MAP was most effective in enhancing vegetative traits such as pseudostem height, pseudostem girth, number of functional leaves per plant, leaf area, chlorophyll content in leaves and number of suckers per plant. In addition, this treatment also recorded early shooting, early maturity, minimum crop duration and highest bunch weight.

Acknowledgement

Authors are thankful to ICAR-AICRP on Fruits, KRC College of Horticulture, Arabhavi under UHS, Balgalkot, Karnataka in India for providing all the necessary facilities during my research period

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