Response of soil applied paclobutrazol for enhancing vegetative and reproductive growth in Kesar mango (Mangifera indica L.)

Introduction

Mango (Mangifera indica L.) belongs to the family anacardiaceae and originated in Indo-Burma region. it is one of the important major fruit of India. It is cross pollinated amphidiploid crop with 2n=2x=40. It is the national fruit of India. It is called as the "King of Fruits" due to its delicious taste, captivating flavour and enticing aroma, excellent flavour attractive appearance and richness in phytochemicals and nutrients (Purseglove, 1972) [12] . Kesar is famous for its excellent fruit quality and delicious flavour. Flowering is an most important step in fruit production. The price of fruit is depends on market demand, so therefore, induction in flowering at certain times is necessary. Biennial bearing or irregular cropping is a major problem in commercial mango cultivation. Mango flowering is an important physiological event that sets the start of fruit production. Mango trees flower in response to the age of the last vegetative flush in the tropical conditions (Davenport 2007) [3] . Synchronization of the vegetative of tree canopies is a necessary first step in the flowering management program. Synchronization of growth is best accomplished by tip pruning all of the stems on the tree. The next step is to decide whether to use PBZ or not. PBZ has been used with considerable success to induce flowering in several fruit crops such as apple, Mango, citrus, pumelo. it reduces vegetative growth and induces water-stress tolerance as well as increases total non-structural carbohydrates (TNC). PBZ has been widely marketed throughout the tropics to stimulate mango flowering. Soil application of PBZ has been found to be more responsive in regard to suppressing the vegetative growth and enhancing the reproductive growth in mango (Nartvaranant et al., 2000) [9] . The first report about the use of paclobutrazol (PBZ) on mango in India was given by Kulkarni (1988) [8] tested concentration of 1.25 to 10 g a.i./tree on the cultivars Dashehari and Banganapalli. The induction of flowering in mango through chemical substances such as paclobutrazol, block the biosynthesis of gibberellins and reduced the growth of plants there by leading to blossoming (Rademacher, 1992) [13] . Applying paclobutrazol to mango plants in July-August promotes inflorescence emergence from October to November leading to fruit maturation from mid-March to April. This timing is highly profitable for farmers due to the high market demand during February-May resulting in higher prices for the produce. Soil application of paclobutrazol enhances yield by curbing vegetative growth and boosting flowering, fruit set, fruit mass, fruit size and overall quality (Burondkar and Gunjate, 1993) [1] . Paclobutrazol plays a critical role in modern mango cultivation, especially for managing tree growth and improving fruiting consistency. Its use has revolutionized mango farming by making production more predictable and efficient. However, proper application timing and dosage are key to achieving the desired results without compromising tree health.

Materials and Methods

The present experiment entitled, "Response of Soil Applied Paclobutrazol for Enhancing Vegetative and Reproductive Growth in Kesar Mango (Mangifera indica L.) was conducted in experimental cum research mango orchard, Department of Horticulture, College of Agriculture, Latur during the year 2023-24. The experiment was carried out on factorial randomized block design with two factors: First factor was concentration of paclobutrazol (C 1 :1 ml a.i/ m², C 2 :1.5 ml a.i/m² and C 3 :2 ml a.i/m²) and Second factor is time of application of paclobutrazol on (M 1 :15 th July, M 2 :1 st August and M 3: 15 th August) experiment having a three replications. The treatment combinations were soil application of paclobutrazol at T1: 15 th July + PBZ 1ml a.i/m²( C 1 M 1 ), T2: 1 August + PBZ 1ml a.i/m² (C 1 M 2 ) , T3: 15 th August + PBZ 1ml a.i/m (C 1 M 3 ) , T4: 15 th July + PBZ 1.5ml a.i/m² (C 2 M 1 ) , T5: 1 August + PBZ 1.5ml a.i/m² (C 2 M 2 ) , T6:15 th August + PBZ 1.5ml a.i/m² (C 2 M 3 ) , T7: 15 th July + PBZ 2ml a.i/m² (C 3 M 1 ) , T8: 1 August + PBZ 2ml a.i/m² (C 3 M 2 ) and T9: 15 th August + PBZ 2ml a.i/m² (C 3 M 3 ). The treatments were applied as per the plan and observation on vegetative, flowering, yield and quality parameters were recorded. Paclobutrazol (PBZ) was applied as a single soil application. The required quantity of paclobutrazol 23% active ingredients was dissolved in 5 liter of water and prepared solution was poured in the ring 1 m from tree trunk as per recommendation. Observations were recorded in respect to shoot length, internodal length, length of panicle and number of panicle per tree manually counted and recorded. For the calculation of days taken to flowering bud initiation, it was counted from cut off date 1 st October to date of appearance of two or three newly emerging flowering bud and average value was worked out.

Results and Discussion

The shoot length of mango was significantly reduced by paclobutrazol application. The shoot length (10.28 cm) was recorded minimum with the dose of paclobutrazol @ 2 ml a.i. (C 3 ) which was at par (11.14 cm) with the dose of paclobutrazol @ 1.5 ml a.i. (C 2 ) and maximum shoot length (11.92 cm) was obtained with the dose of paclobutrazol @ 1 ml a.i. (C 1 ) respectively. Paclobutrazol can enhance the total phenolic content in terminal buds and alter the phloem to xylem ratio in the stem which is crucial for restricting vegetative growth and promoting flowering by modifying assimilate partitioning and nutrient supply patterns for new growth. PBZ could also induce flowering in mango trees because it reduced vegetative growth. The involvement of the GA in mango was also demonstrated by Yamashita et al.1997, who reported that GA acts as a flowering inhibitor. Similar results were observed by Kulkarni (1988) [8] in the Banganpalli, Dashehari and Peddarasam cultivars, Reddy and Kurian and (2008) [15] .

The data revealed that the variation in shoot length was found significant. The shoot length of mango was significantly reduced by different time of paclobutrazol application. Minimum shoot length (9.77 cm) was noted at application of paclobutrazol on 15 th July (M 1 ) which was at par (11.22 cm) noted with the application of paclobutrazol on 1 st August (M 2 ) and maximum shoot length (12.35 cm) was recorded at the application of paclobutrazol on 15 th August (M 3 ) respectively. Paclobutrazol is a plant growth regulator that inhibits gibberellin biosynthesis, when paclobutrazol is applied it interferes with the normal production of gibberellins leading to reduced cell elongation and consequently shorter shoot length. Same result found by with the earlier findings of paclobutrazol influence on shoot growth of mango by Ram & Tripathi (1993) [14] , Chavan (2023) [2] and Gohel et al. (2021) [5] in kesar mango.

The interaction effect of time and dose of paclobutrazol application on shoot length were found non-significant.

The internodal length significantly reduced by the paclobutrazol application. The internode length (2.17 cm) was recorded minimum with the dose of paclobutrazol appliaction @ 2 ml a.i. (C 3 ) and maximum length of internode (2.69 cm) was obtained with the dose of paclobutrazol application @ 1 ml a.i. (C 1 ). Paclobutrazol act as a plant growth regulator that primarily functions by inhibiting gibberellin biosynthesis hormone responsible for promoting cell elongation and plant growth. When paclobutrazol is applied to plants it slows down vegetative growth leading to shorter more compact plants with smaller leaves and reduced internode lengths. This observation is in agreement with the earlier findings of Khader (1991) [7] in dashaheri mango, Salazar-garcia and Vazquez-valdivia (1997) [16] in Tommy Atkins mango.

Minimum internodal length (2.29 cm) was noted at application of paclobutrazol on 15 th August (M 3 ) which was at par (2.39 cm) noted at the application on 1 st August (M 2 ) and maximum internodal length (2.42 cm) was recorded at application of paclobutrazol on 15 th July (M 1 ). Paclobutrazol is a plant growth regulator that inhibits gibberellin biosynthesis leading to reduced stem elongation and shorter internodal lengths. Paclobutrazol works by inhibiting the synthesis of gibberellins. A group of plant hormones responsible for promoting cell elongation and division. This results in reduced cell elongation. This observation are in agreement with the earlier findings of paclobutrazol influence on shoot growth of mango Ram and Tripathi (1993) [14] and Reddy and Kurian (2008) [15] .

The interaction effect of time and dose of paclobutrazol application on internodal length were found non-significant.

Days of panicle emergence Effect of dose (C)

The days of panicle emergence of mango was significantly reduced by paclobutrazol application however, the effect was more pronounced in the higher concentrations than the lower concentration. Days of panicle emergence (46.89) was recorded minimum with the dose of paclobutrazol @ 2 ml a.i. (C3) which was at par (51.12) recorded with the dose of paclobutrazol @ 1 ml a.i. (C1) and maximum days of panicle emergence (52.73) was obtained with the dose of paclobutrazol @ 1.5 ml a.i. (C2). All the available evidence opined that carbohydrate reserves played an important role in flower bud differentiation and they provide conditions favorable for the synthesis of substances which are required for flower bud differentiation. The high C:N ratio during flower bud differentiation was ascribed to the increased carbohydrate availability and considered as an important factor in regulation of flowering in fruit crops.This finding is similar to Gohel et al., (2021) [5] in kesar mango and Sarker and Rahim (2012) [17] , where paclobutrazol induced flowering 85 days after treatment application. The total activity of auxin-like substances increased the higher starch reserve, total carbohydrates and higher C: N ratio in the shoots favour flower bud initiation in mango (Jogdande and Choudhari (2001) [6] .

Minimum days required for the panicle emergence (46.33) was noted at application of paclobutrazol on 15 th July (M 1 ) however maximum days required for the panicle emergence (54.77) was recorded at application of paclobutrazol on 15 th August (M 3 ). The application of paclobutrazol in mid-July suppressed vegetative growth and induced early and profuse flowering during the investigation. In other words the flower inductive cycle which is part of the phenological and physiological cycle of the Mango tree may commence earlier in the season but flowering is delayed by the inhibitor until sufficient promoter builds up to counteract the inhibitor. Paclobutrazol appears to help achieve this stage much earlier due to its inhibitory activity. This hypothesis is particularly compelling when considering the flowerinhibitory role of gibberellins in trees and the antigibberellin activity of paclobutrazol as observed by Kulkarni (1988) [8] and Padhiar (1999) [10] in mango. The results of the present investigation showed that paclobutrazol induced early flowering, advanced fruit maturity and provided opportunities for the commercial advantages of early-season marketing. These findings are consistent with the results obtained by Kulkarni (1988) [8] in mango, Sarker and Rahim (2018) [18] in Amrapali. Chavan (2023) [2] and Gohel et al. (2021) [5] in Kesar mango.

The data showed that minimum days of panicle emergence was recorded in the treatment combination of C 3 M 1 (45.04) which was at par with treatment C 2 M 1 and C 3 M 2 (46.70) and maximum number of days required for panicle emergence recorded in the treatment combination of C 2 M 3 (58.95) These findings are consistent with the results obtained by Sarker and Rahim (2018) [18] in Amrapali, Chavan (2023) [2] in Kesar mango and Gohel et al. (2021) [5] in Kesar mango.

Number of panicle per tree Effect of dose (C)

The effect of different dose of paclobutrazol on number of panicle per tree was found significant. Number of panicle per tree (621.68) was recorded maximum with the dose of paclobutrazol @ 2 ml a.i. (C 3 ) which was at par (564.90) with the dose of paclobutrazol @1.5 ml a.i. (C 2 ) and minimum number of panicle per tree (516.13) was obtained with the dose of paclobutrazol @1 ml a.i. (C1). Yeshitela et al. (2004) [20] reported that increased number of panicles for paclobutrazol treated plants is due to lower expenditure of tree reserves to the vegetative growth parameters and consequently no assimilates limitations, compared with an excessive vegetative growth in the control trees. This observation are in agreement with the earlier findings of paclobutrazol influence on the days of panicle emergence Burondkar and Gunjate (1993) [1] , Chavan (2023) [2] and Gohel et al., (2021) [5] in Kesar mango.

Maximum number of panicle per tree (618.68) was recorded at application of paclobutrazol on 15 th July (M 1 ) which was at par (552.85) was noted at application of paclobutrazol on 1 st August (M 2 ) and minimum number of panicle per tree (531.18) was noted at application of paclobutrazol on 15 th August (M 3 ). Paclobutrazol known to decrease vegetative growth rate through early cessation of growth which results in the accumulation of carbohydrates in trees and slightly decreasing the total nitrogen in the terminal shoots which favours flowering by maintaining high C: N ratio in the shoots.

The interaction effect of time and dose of paclobutrazol application on number of panicle per tree were also found non-significant.

The effect of different dose of paclobutrazol on length of panicle was found significant. The length of panicle of mango was significantly increased by paclobutrazol application however, Maximum length of panicle (31.63 cm) was obtained with the dose of paclobutrazol @ 2 ml a.i. (C 3 ) which was at par (29.47 cm) was recorded with the dose of paclobutrazol @ 1.5 ml a.i. (C 2 ) and minimum length of panicle (27.99 cm) was obtained with the dose of paclobutrazol @ 1 ml a.i. (C 1 ).This observation are in agreement with the earlier findings of paclobutrazol influence on the length of panicle by Desai and Chundawat, (1994) and Sarkar and Rahim (2018) [18] in Amrapali.

The data revealed that the variation in length of panicle was found significant as influenced by different time of paclobutrazol application. Maximum length of panicle (34.69) was recorded at application of paclobutrazol on 15 th July (M 1 ) which was at par (27.88) was noted at application of paclobutrazol on 1 st August (M 2 ) and minimum length of panicle (26.52) was noted at application of paclobutrazol on 15 th August (M 3 ) respectively. This observation is in agreement with the earlier findings of paclobutrazol influence on the length of panicle by Ram and Tripathi (1993) [14] , Sarkar and Rahim (2018) [18] in Amrapali Gohel et al. (2021) [5] and Chavan (2023) [2] in Kesar.

Meanwhile, the interaction between different time and dose of paclobutrazol application on length of panicle was found non-significant.

Conclusion

The present investigation, based on Response of soil applied paclobutrazol for enhancing vegetative and reproductive growth in Kesar mango (Mangifera indica L.), led to the following conclusions: Treatment with a concentration of paclobutrazol at 2 ml a.i per meter of canopy diameter had a significant positive impact on vegetative parameters and flower parameters of mango. The application of paclobutrazol on July 15th was found to have the most beneficial effects on vegetative parameters as well as flower parameters of mango. The interaction effect of paclobutrazol applied at 2 ml per meter of canopy diameter on July 15th was the most effective in achieving early emergence of panicles.

References

1. Burondkar MM, Gunjate RT. Control of vegetative growth and induction of regular and early cropping in Alphonso mango with paclobutrazol. Acta Horticulturae. 1993;341:206-215.
2. Chavan GE. Standardization of dose and time of application of paclobutrazol in mango (Mangifera indica L.) var. Kesar under Marathwada condition [M.Sc. thesis]. Parbhani: Vasantrao Naik Marathwada Krishi Vidyapeeth; 2023.
3. Davenport TL. Reproductive physiology of mango. Brazilian Journal of Plant Physiology. 2007;19:363376.
4. Desai MM, Chundawat BS. Regulation of flowering in mango by paclobutrazol. Indian Journal of Horticulture. 1994;51(1):9-15.
5. Gohel BC, Malam VR, Mishra S, Solanki M, Patel VS. Effect of soil applied paclobutrazol at different times on growth and flowering of mango (Mangifera indica L.) cv. Kesar. The Pharma Innovation Journal. 2021;10(10):318-321.
6. Jogdande ND, Choudhari KG. Seasonal changes in auxin content and its role in flowering of mango (Mangifera indica L.). Orissa Journal of Horticulture. 2001;29(2):10-12.
7. Khader SESA. Control of tree height, trunk girth, shoot growth and total assimilation in young grafted mango trees by paclobutrazol. Indian Journal of Horticulture. 1991;48(2):112-115.
8. Kulkarni VJ. Chemical control of tree vigour and the promotion of flowering and fruiting in mango (Mangifera indica L.) using paclobutrazol. Journal of Horticultural Science. 1988;63(3):557-566.
9. Nartvaranant P, Subhadrabandhu S, Tongumpai P. Practical aspects in producing off-season mango in Thailand. Acta Horticulturae. 2000;509:661-668.
10. S.K. Nagar: Gujarat Agricultural University; 1999.
11. Panse VG, Sukhatme PV. Statistical Methods for Agricultural Workers. New Delhi: Indian Council of Agricultural Research; 1985.
12. Purseglove JW. Mangoes west of India. Acta Horticulturae. 1972;24:107-174.
13. Rademacher W. Biochemical effects of plant growth retardants. Plant Biochemical Regulators. 1992;169200.
14. Ram S, Tripathi R. Effect of paclobutrazol on flowering and fruiting of Dashehari mango. Journal of Horticultural Science. 1993;68(1):45-50.
15. Reddy YTN, Kurian RM. Cumulative and residual effects of paclobutrazol on growth, yield and fruit quality of Alphonso mango. Journal of Horticultural Sciences. 2008;3(2):119-122.
16. Salazar-Garcia S, Vazquez-Valdivia V. Physiological persistence of paclobutrazol on the Tommy Atkins mango (Mangifera indica L.) under rainfed conditions. Journal of Horticultural Science. 1997;72(2):339-345.
17. Sarker BC, Rahim MA. Vegetative growth, harvesting time, yield and quality of mango (Mangifera indica L.) as influenced by soil drench application of paclobutrazol. Bangladesh Journal of Agricultural Research. 2012;37(2):335-348.
18. Sarker BC, Rahim MA. Influence of paclobutrazol on growth, yield and quality of mango. Bangladesh Journal of Agricultural Research. 2018;43(1):1-12.
19. Yamashita K, Kitazono K, Iwasaki S. Flower bud differentiation of Satsuma Mandarin as promoted by soil-drenching treatment with IAA, BA or paclobutrazol solution. Journal of the Japanese Society for Horticultural Science. 1997;66(1):67-76.
20. Yeshitela T, Robbertse PJ, Stassen PJC. Paclobutrazol suppressed vegetative growth and improved yield as well as fruit quality of 'Tommy Atkins' mango (Mangifera indica) in Ethiopia. New Zealand Journal of Crop and Horticultural Science. 2004;32(3):281-293.