Tithonia diversifolia (Hemsl.) A. Gray, is a notable aromatic medicinal plant, originated from Mexico and Central America. It is commonly known as Mexican sunflower and is classified under one of the flowering family, Asteraceae. The plant is a weed, moderately resistant to draught and is pantropical in its distribution (Kawini et al., 2017). Traditional healing uses of different parts of T. diversifolia, particularly leaves and flowers by indigenous people have been well documented. The plant is used though oral administration for treatment of diabetics, malaria, hepatitis, fever and other infectious diseases and several in-vivo and in-vitro studies on the ethno-pharmacological effects of T. diversifolia has provided heterogeneous evidence supporting majority of the beneficial therapeutic claims of the plant (Tagne et al., 2018). The presence of phenolic compounds such as tannins and particularly flavonoids enhanced several therapeutic activities including anti-inflammatory, anti-cancer, anti-malarial, antioxidant and antimicrobial activities of T. diversifolia (Oyewole et al., 2008; Thongsom et al., 2013; da Gama et al., 2014; Gaicomo et al., 2015; Dlamini et al., 2020). Because of the high potassium content in the leaves, the plant is also used as green manure for enhancement of soil fertility (Jama et al., 2000).
T. diversifolia, like other aromatic and medicinal plants has huge antimicrobial properties with high potency against both bacterial and fungal pathogens. Aqueous and ethanolic extracts of T. diversifolia leaves have shown effective inhibitory action against bacterial pathogens Escherichia coli and Salmonella typhi and fungus Candida albicans (Olayinka et al., 2014). Leaf extracts of T. diversifolia has also been reported to possess inhibitory effects against destructive fungal pathogens including Aspergillus niger, Colletotrichum gloeosporoides, Fusarium oxysporium, Gloeotrichum candidium and Phytopthora nicotianae (Rejeki et al., 2017; Ngegba et al., 2018; Awere et al., 2020; Chege and Kimaru, 2021). The plant is also reported to have strong inhibitory effect against potato wilt causal agent Ralstonia solanacearum (Opondo et al., 2023). Because of its strong fungicidal and bacteriosidal propertis, biofungicidal formulations have been manufactured which has shown promising control against Pythium myriotylum, the causal agent of root rot of Xanthomonas sagittifolium (Flore et al., 2023).
Alternaria brassicicola (Schwein) Wiltshire is a fungal plant pathogen well-known for causing one of the most devastating diseases called black spot disease in Brassicaceae members, many of which are of agricultural and economic importance. It is spread by wind, rain and insects and has the ability to survive and sporulate even in plant debris under favourable temperature and moisture content. Control of A. brassicicola in India hugely relies on chemical fungicides which remain a serious human and environmental threat (Gupta et al., 2020). Till date, convincing measure to bring about effective biological control of A. brassicicola diseases such as mustard blight of mustard plant and black spot disease of cabbage remain a huge challenge. Recent researches has focused on the use of plant growth promoting bacteria such as Psuedomonas fluorescens, Bacillus subtilus and B1 bacterial strains has shown some positive results (Sabry and Ali, 2016; Gupta et al., 2020). Use of the well-known antagonistic, Trichoderma viridei and also T. harzianum has also shown certain promising result in biocontrol of the pathogen (Sabry and Ali, 2016; Khalse et al., 2017). The present study reveals the potency of T. diversifolia leaf extracts against the test pathogen, A. brassicicola.