Evaluation of antifungal activities of some Indian dietary spices against pathogenic Rhizopus arrhizus and Rhizopus stolonifer

Rhizopus arrhizus and Rhizopus stolonifer are pathogenic fungi responsible for causing ‘soft rot’ disease in fruits and vegetables, as well as life-threatening ‘mucormycosis’ in animals and humans, especially immunocompromised hosts. The use of synthetic fungicides and chemical preservatives to inhibit microbes is being challenged due to their toxic effects on human health and the environment. This has prompted researchers to investigate novel antimicrobials that are natural and safe. Current study aimed to evaluate the antifungal activities of essential oils (EOs), powdered (PWD) forms, and water extracts (WEs) of ten Indian dietary spices (Allium sativum (Als), Brassica nigra (Brn), Cinnamomum zeylanicum (Ciz), Cuminum cyminum (Cuc), Curcuma longa (Cul), Mentha piperita (Mep), Ocimum sanctum (Ocs), Syzygium aromaticum (Sya), Trigonella foenum-graecum (Trf), and Zingiber officinale (Zio)) against R. arrhizus (NCIM877) and R. stolonifer (NCIM1139). Spice agar method was used for investigating antifungal potential of PWD spices. Impregnated paper disc method and broth dilution technique were followed for screening the antifungal activities of EOs and WEs. Results revealed that EOs of six spices (Als, Brn, Ciz, Cuc, Mep, Sya), and PWD forms of four spices (Brn, Ciz, Cuc, Sya) inhibited the growth of both fungi in culture media, effectively. WEs of all ten spices remained ineffective in arresting the growth of tested fungal strains. R. stolonifer was found more sensitive compared to R. arrhizus towards tested substances. Based on these findings, further in vivo studies on PWD forms of Ccb, Ccm, and Sya and EOs of Als, Brn, Ccb, Ccm, Mep, Ocs and Sya may establish spices as ‘botanical antimicrobials’ to prolong the shelf life of valuable horticultural crops by arresting the growth of R. arrhizus and R. stolonifer.