Study of the Interaction of Auxin and Cytokinin Levels on Morphological, Traits and Yield Components of Cowpea (Vigna unguiculata L.) Cultivars

Document Type : Original Article

Authors

Mohsen Pourfarokhi ¹

Shahram Lak ¹

Nasser Zarifinia ²

Tayeb Sakinejad ¹

Mani Mojddam ¹

¹ Department of Agriculture, Islamic Azad University, Ahvaz Branch, Iran

² Horticultural Sciences Research Institute, Sabzi Vasifi Research Institute, Safi Abad Agricultural and Natural Resources Research Center, Agricultural Research, Education and Extension Organization (AREEO), Dezful, Iran

10.22067/ijpr.2026.95948.1120

Abstract

Introduction
Legumes hold a special position in sustainable agriculture and the global cropping pattern. These plants, by establishing symbiosis with nitrogen-fixing bacteria of the genus Rhizobium, are capable of converting atmospheric molecular nitrogen into a form absorbable by the plant. This characteristic, while reducing dependence on nitrogenous chemical fertilizers, leads to improved soil fertility and increased productivity in crop rotation. Among legumes, cowpea (Vigna unguiculata L.) is of particular importance due to its unique physiological and nutritional characteristics. This species, traditionally cultivated in arid and semi-arid regions such as northern Khuzestan, is an ideal option for cultivation under climate change conditions due to its favorable adaptation to environmental stresses (drought and heat). The high nutritional value of this crop (18-32% protein and essential amino acids) has made it a cost-effective substitute for animal protein sources. Plant hormones, as key signaling molecules, play a decisive role in modulating physiological processes and enhancing the performance efficiency of plants. Auxins, particularly indole-3-acetic acid (IAA), are effective in nitrogen fixation through increasing cell dimensions, vascular differentiation, and nodulation. Cytokinins also determine final yield by stimulating cell division, inhibiting leaf senescence, and regulating the transfer of photosynthetic materials to storage organs. The interaction of these two hormones in regulating the source-sink ratio and allocation of photosynthates to seeds is of particular importance. The innovation of this research lies in investigating the interactive effects of different levels of auxin and cytokinin on the morpho-physiological characteristics and yield of cowpea cultivars (Mashhad, Mahali, and Arabic) under the climatic conditions of Dezful. Despite scattered studies on the individual effects of these hormones, there is no comprehensive information regarding the optimal concentrations for their combined application and the differential response of cultivars. This research is designed with the aim of quantifying the growth and reproductive responses of cultivars to the combined application of auxin and cytokinin and identifying the best cultivar-hormone combination for sustainable yield increase.
 
Materials and Methods
This research was conducted during two crop years (2021-2022) at the Safiabad Agricultural and Natural Resources Research Center in Dezful. The experiment was designed as a factorial split-plot arrangement based on a randomized complete block design with three replications. Main plots consisted of three cowpea cultivars (Mashhad, Mahali, and Arabic), and sub-plots included factorial combinations of three auxin concentrations (0, 200, and 400 mg.L^-1) and three cytokinin concentrations (0, 100, and 200 mg.L^-1). Each experimental plot comprised 10 planting rows, 10 meters long, with a row spacing of 75 cm and a plant spacing of 20 cm.
Hormone foliar application was performed at the beginning of the flowering stage (60 days after planting). Measured traits included grain yield, biological yield, number of branches per plant, number of pods per plant, pod length, number of seeds per pod, and 100-seed weight. Combined analysis of variance for the data from two crop years was performed considering the year effect as a random factor and the effects of cultivar, auxin, cytokinin, and their interactions as fixed factors. Means were compared using Duncan's multiple range test at a five percent probability level using SAS software (version 9.2). Correlation coefficients between traits were calculated using Pearson's method in SPSS software (version 26), and graphs were drawn using Excel software (version 2013).
 
Results and Discussion
The results showed that the combined application of auxin 400 mg.L^-1 and cytokinin 200 mg.L^-1 resulted in superior performance in most traits compared to control treatments and individual hormone applications. The highest number of seeds per pod (12.7), pod length (16.7 cm), number of branches (14), and grain yield (2346 kg.ha^-1) were observed in the Mashhad cultivar, while the highest number of pods per plant (45.6) and biological yield (5226 kg.ha^-1) were observed in the Mahali cultivar under the same treatment. On average, hormone application caused a 24% increase in grain yield, with the Mashhad cultivar showing the greatest response. Combined analysis of variance showed that the three-way interaction (cultivar × auxin × cytokinin) was significant for biological yield, number of branches, number of pods per plant, and 100-seed weight. Two-way interactions were significant for grain yield, pod length, and number of seeds per pod. The highest grain yield (2346 kg.ha^-1) was obtained from the treatment of Mashhad cultivar with auxin 400 mg.L^-1 and cytokinin 200 mg.L^-1 (V1A2C2). This treatment also resulted in maximum biological yield (5661 kg.ha^-1), number of branches (12.8), number of pods per plant (45.6), pod length (16.0 cm), and number of seeds per pod (12.7). The lowest values were observed in the control treatment of the Arabic cultivar. It appears that the application of auxin and cytokinin, by improving hormonal balance, increasing photosynthetic efficiency, and optimizing source-sink relationships, has led to increased pod formation, improved seed growth, and ultimately enhanced yield. Correlation analysis showed a significant positive correlation between grain yield and biological yield (r = 0.75) and between the number of pods per plant and biological yield (r = 0.72). Pod length had a very strong correlation with the number of seeds per pod (r = 0.88) and 100-seed weight (r = 0.89).
 
Conclusions
The results indicated that the combined foliar application of the plant hormones auxin and cytokinin had a significant effect on improving the morphological traits, yield components, and grain yield of cowpea. The Mashhad cultivar showed the greatest positive response to hormone application, and the treatment of auxin 400 mg.L^-1 along with cytokinin 200 mg.L^-1 on this cultivar was identified as the most effective combination for maximizing yield impact. Therefore, the combined application of these hormones at the mentioned concentrations on high-potential cultivars like Mashhad can be recommended as an effective strategy to enhance cowpea productivity in regions similar to the climatic conditions of northern Khuzestan province.
 
Acknowledgement
The authors express their gratitude to the Safiabad Agricultural and Natural Resources Research Center in Dezful for their support in conducting this research.

Keywords

Number of pods per plant

Number of side branches

Plant hormone

Pod length

Sustainable agriculture

100-seed weight

Subjects

• Agronomy

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Authors retain the copyright. This is an open access article distributed under Creative Commons Attribution 4.0 International License (CC BY 4.0)

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