Effect of GA3 and NAA on Okra Growth and Yield: A Field Trial on cv. Parbati in Sunsari, Nepal

What did the okra growth regulator trial find?

Foliar sprays of plant growth regulators raised both the growth and the pod yield of okra (Abelmoschus esculentus) cv. Parbati in a spring 2025 field trial at the Agriculture Research Station, Tarahara, Sunsari district, Nepal. The headline result is that the best treatment for growth was not the best treatment for yield. A tank mix of 100 ppm GA₃ + 100 ppm NAA produced the tallest plants and the largest leaves, while NAA at 150 ppm applied alone gave the most pods per plant, the heaviest pods and the highest total pod yield: 9.55 t ha^-1 against 3.39 t ha^-1 in the water-sprayed control, an increase of 181.7%.

The study was published in Tropical Agroecosystems 7(2): 59–64 (DOI 10.26480/taec.02.2026.59.64). Manwee Gupta is first author; Bishal Neupane is second and corresponding author. According to the article's author-contribution statement, Gupta led conceptualisation, field investigation, data curation, formal analysis and the original draft, while Neupane contributed methodology, formal analysis, review and editing, and supervision.

Why test GA3 and NAA on okra in the Eastern Terai?

Okra, known in Nepal as bhindi, is grown mainly in the Terai and mid-hills. Citing Ministry of Agriculture and Livestock Development statistics for 2021/22, the paper reports a national okra area of 9,397 ha and a mean yield of 11.95 t ha^-1, and argues that this reflects under-use of the crop's potential, partly because low-input physiological tools such as plant growth regulators (PGRs) are rarely used by farmers.

The two regulators tested act differently. Gibberellic acid (GA₃) promotes stem elongation and leaf expansion, so its effects were expected to show first in plant height and leaf size. Naphthalene acetic acid (NAA), a synthetic auxin, reduces premature abscission of flowers and young fruits, so its effects were expected mainly in pod number and pod yield. Because PGR responses are concentration-dependent and often non-linear, the authors tested two rates of each compound, alone and in combination, rather than a single dose.

How the experiment was designed

• Site and season: Agriculture Research Station, Tarahara, Sunsari (136 m above sea level), sown in mid-March 2025 (first week of Chaitra).
• Design: randomised complete block design (RCBD), seven treatments, three replications, 21 plots.
• Plots: 3.0 m × 1.5 m, 25 plants per plot at 60 cm × 30 cm spacing; five tagged plants per plot used for plant-level measurements.
• Treatments: T1 control (water spray); T2 100 ppm GA₃; T3 150 ppm GA₃; T4 100 ppm NAA; T5 150 ppm NAA; T6 100 ppm GA₃ + 100 ppm NAA; T7 150 ppm GA₃ + 150 ppm NAA.
• Application: foliar sprays to run-off at 30 and 45 days after sowing (DAS) with a knapsack sprayer; control plots received an equal-volume water spray on the same dates. Both sprays were completed before the first pod harvest.
• Analysis: single-factor ANOVA for RCBD, means separated by Fisher's LSD at p ≤ 0.05, in R 4.2.2 and Microsoft Excel.

One detail worth noting for students: because the treatment set pairs each regulator with two rates but is not a complete factorial, the authors analysed the seven treatments as a single factor rather than as a regulator × concentration factorial. Pod yield was measured on the whole plot, while pods per plant and pod weight came from the tagged sub-sample, so the yield figure is an independent measurement rather than a product of the other two.

Treatment results: growth and yield of okra cv. Parbati

Treatment effects were highly significant (p < 0.001) for every growth and yield-attributing trait except stem diameter at 45 DAS. The table below brings together the main growth and yield values from the article's Tables 1 and 2. Means in a column sharing a letter are not significantly different (LSD, p ≤ 0.05).

Source: Gupta and Neupane (2026), Tables 1 and 2. CV for pod yield was 8.26% and LSD (0.05) was 0.93 t ha^-1.

Growth: the combination built the biggest canopy

T6 (100 ppm GA₃ + 100 ppm NAA) produced the tallest plants at 30, 60 and 75 DAS. At 75 DAS it reached 100.87 cm, 54.9% taller than the control. It also gave the longest leaves (21.27 cm, 62.7% above the control) and, statistically level with NAA 150 ppm, the widest leaves (20.67 cm against 16.53 cm in the control). The control was the shortest treatment at every recording date.

Yield: NAA at 150 ppm was clearly best

NAA at 150 ppm gave 8.24 pods per plant (107.6% above the control) and 66.82 g pods (73.7% above the control), and its pod yield of 9.55 t ha^-1 was significantly above every other treatment. NAA at 100 ppm (7.39 t ha^-1) and GA₃ at 150 ppm (6.68 t ha^-1) ranked next. The two combinations gave the lowest yields of any regulator treatment, and T6, the growth leader, ranked last among them at 5.17 t ha^-1.

Why did the best-growing treatment give a lower yield?

This divergence between growth and yield rankings is the most useful result of the trial. The authors offer two explanations that are consistent with the data. The first is hormonal balance: combining two regulators raises the total exogenous load, and excess auxin can interfere with fruit set. The second is sink competition: the combined treatments built the largest canopy, and assimilate allocated to leaves and stems may have come at the expense of developing pods. The paper is explicit that its design cannot separate these explanations, because dry-matter partitioning and flower and fruitlet drop were not measured.

Yield rose from 100 to 150 ppm in both single-regulator series, with no decline at the higher rate. The optimum NAA rate in this environment therefore lies at or above 150 ppm and was not bracketed by the experiment.

What this means for okra growers

On this evidence, the authors identify foliar NAA at 150 ppm, sprayed at 30 and 45 DAS, as the treatment to carry forward for okra in the Eastern Terai. They also caution that confirmation across multiple seasons, sites and cultivars, a wider concentration range and an economic assessment are needed before a blanket recommendation is made to growers. A practical point for anyone reading the growth data: a taller, leafier okra plant is not necessarily a higher-yielding one, so canopy size alone is a poor guide to the value of a PGR treatment.

What this means for researchers and students

• Record both growth and yield traits; a study stopping at plant height would have chosen the wrong treatment here.
• Include rates high enough to find the peak of the response curve. Here the NAA optimum was not reached.
• Measure partitioning (dry matter by organ) and flower or fruit drop if the aim is to explain why combinations underperform.
• When the treatment set is not a full factorial, analyse it as a single factor, as this paper does.

A companion okra study by Neupane and colleagues at Katahari, Morang, accepted in TURJAF, tested NAA and GA₃ under different conditions; see the summary of the Katahari okra trial. For a step-by-step guide to running this kind of analysis, see analysing RCBD field trials in R with agricolae.

Limitations

The authors list several constraints. The trial ran for one season at one site with one cultivar, so season and site interactions cannot be assessed. No phenological data were recorded. Yields are total rather than marketable, since no marketable/unmarketable split was made. No residue analysis was performed, and the paper makes no claim about residue safety, although both sprays were completed before the first picking. Comparisons with published work sometimes involve different cultivars and spray schedules.

How to cite this study

Gupta, M. and Neupane, B. (2026). Effect of Different Plant Growth Regulators on Growth and Yield of Okra (Abelmoschus esculentus (L.) Moench) cv. Parbati in Sunsari District, Nepal. Tropical Agroecosystems, 7(2): 59–64. https://doi.org/10.26480/taec.02.2026.59.64

The full list of Bishal Neupane's articles is on the publications page, and the field and statistical methods he uses are described on the methods page. Supervisors or collaborators interested in this line of work are welcome to get in touch through the contact page.