*Article* **Allelopathic Potential and Active Substances from** *Wedelia Chinensis* **(Osbeck)**

**Kawsar Hossen 1,2, Krishna Rany Das 1,2,3, Shun Okada 1,2, Arihiro Iwasaki 4, Kiyotake Suenaga <sup>4</sup> and Hisashi Kato-Noguchi 1,2,\***


Received: 25 September 2020; Accepted: 30 October 2020; Published: 2 November 2020

**Abstract:** *Wedelia chinensis* (Asteraceae) is a wetland herb native to India, China, and Japan. It is a valuable medicinal plant recorded to have pharmaceutical properties. However, the phytotoxic potential of *Wedelia chinensis* has not yet been examined. Thus, we carried out this study to establish the allelopathic effects of *Wedelia chinensis* and to identify its phytotoxic substances. Extracts of *Wedelia chinensis* exhibited high inhibitory activity against the root and shoot growth of cress, alfalfa, rapeseed, lettuce, foxtail fescue, Italian ryegrass, timothy, and barnyard grass. The inhibition was varied with species and was dependent on concentrations. The extracts were separated through several purification steps, and the two effective substances were isolated and characterized as vanillic acid and gallic acid using spectral analysis. Vanillic acid and gallic acid significantly arrested the growth of cress and Italian ryegrass seedlings. The concentrations of vanillic acid and gallic acid needed for 50% inhibition (I50 values) of the seedling growth of the cress and Italian ryegrass were 0.04–15.4 and 0.45–6.6 mM, respectively. The findings suggest that vanillic acid and gallic acid may be required for the growth inhibitory activities of *Wedelia chinensis*.

**Keywords:** *Wedelia chinensis*; organic farming; phytotoxic substances; vanillic acid; gallic acid

## **1. Introduction**

Organic farming emerged at the beginning of the 20th century as an alternative agricultural method to demote the hazardous effect of nonnatural herbicides on the environment and people [1,2]. Natural substances are used in organic farming, and at the same time, the use of synthetic substances is banned or severely restricted [3]. Organic farming needs various types of agricultural crop that help to sustain beneficial microorganisms in the soil and to enhance soil conservation to increase farm production. Accordingly, weeds should be controlled without applying chemical herbicides that cause enormous problems [4]. Thus, searching for nature-based product alternatives to synthetic herbicides is now a pressing issue to control weeds, which is a major impediment to crop production [5,6]. In light of these concerns, allelopathy can be explored and used as alternative weed management over synthetic herbicides [7]. Many studies have reported on the use of phytotoxic substances as a nature-friendly approach to weed management [7–9].

The perennial herb *Wedelia chinensis* from the Asteraceae family is usually named Wedelia in Chinese, bhringraj in Hindi, and manjal karisalanganni in Tamil [10]. *Wedelia chinensis* is a climbing herb that is introduced in submerged areas in Assam, Uttar, and Andhra Pradesh and in offshore areas of India. It is also grown in the Madras Presidency of India, Japan, and China [11,12]. The herb is a fragile, expanding, and hairy-type plant, with branches usually up to 50 cm long.

The leaf architecture is simple, arranged oppositely with subsessile leaflets and short, white hairs. Its flower is an axillary head and yellow. The fruits are nearly oval with hairs on the surface [13–15]. The literature reports that different parts (leaves, stems, and roots) of *Wedelia chinensis* are applied as hepatoprotection and a cholagogue and as folk medicine to treat various diseases such as diarrhea, jaundice, cough, diphtheria, headache, and pertussis; to help relieve mental stress; and to promote sleep [16,17]. Conventionally, the leaves, stems, and fruits are used in childbirth and to treat bites and stings, kidney dysfunction, fever, amenorrhea, infection, and wounds [18]. Leave extracts are a natural way to generally apply anti-inflammatory medicines such as Dolonex (Piroxicam) Brufen, and Voveran [13].

Pharmacological investigations have revealed that *Wedelia chinensis* had effects on diterpenoids, sesquiterpenes, triterpenoids, flavonoids, organic acids, and steroids [19,20] and has antioxidant [21,22], anti-inflammatory and antimicrobial [23], and anticancer effects [24]. Moreover, *Wedelia chinensis* is a common garden herb that tends to form a community, and field investigations have shown that there are few weeds in its community [25]. Although *Wedelia chinensis* is known to contain many pharmaceutical features, the allelopathic effects of this plant have not yet been recorded in the literature. Therefore, the study was conducted to explore the allelopathy and to identify the allelochemicals from *Wedelia chinensis*.

## **2. Materials and Methods**
