Garlic, from Remedy to Stimulant: Evaluation of Antifungal Potential Reveals Diversity in Phytoalexin Allicin Content among Garlic Cultivars; Allicin Containing Aqueous Garlic Extracts Trigger Antioxidants in Cucumber.

Zhihui Cheng,Sikandar Hayat,Muhammad Ali,Husain Ahmad,Xuejin Chen,Mengyi Wang

doi:10.3389/fpls.2016.01235

Abstract

Garlic has the charisma of a potent remedy and holds its repute of a therapeutic panacea since the dawn of civilization. An integrated approach was adopted to evaluate the genetic diversity among Chinese garlic cultivars for their antifungal potency as well as allicin content distribution and, furthermore; a bioassay was performed to study the bio-stimulation mechanism of aqueous garlic extracts (AGE) in the growth and physiology of cucumber (Cucumis sativus). Initially, 28 garlic cultivars were evaluated against four kinds of phytopathogenic fungi; Fusarium oxysporum, Botrytis cinerea, Verticillium dahliae and Phytophthora capsici, respectively. A capricious antifungal potential among the selected garlic cultivars was observed. HPLC fingerprinting and quantification confirmed diversity in allicin abundance among the selected cultivars. Cultivar G025, G064, and G074 had the highest allicin content of 3.98, 3.7, and 3.66 mg g-1, respectively, whereas G110 was found to have lowest allicin content of 0.66 mg g-1. Cluster analysis revealed three groups on the basis of antifungal activity and allicin content among the garlic cultivars. Cultivar G025, G2011-4, and G110 were further evaluated to authenticate the findings through different solvents and shelf life duration and G025 had the strongest antifungal activity in all conditions. minimum inhibitory concentration and minimum fungicidal concentration of Allicin aqueous standard (AAS) and AGE showed significant role of allicin as primary antifungal substance of AGE. Leaf disk bioassay against P. capsici and V. dahliae to comparatively study direct action of AGE and AAS during infection process employing eggplant and pepper leaves showed a significant reduction in infection percentage. To study the bioactivity of AGE, a bioassay was performed using cucumber seedlings and results revealed that AGE is biologically active inside cucumber seedlings and alters the defense mechanism of the plant probably activating reactive oxygen species at mild concentrations. However, at higher concentrations, it might cause lipid peroxidation and membrane damage which temper the growth of cucumber seedlings. At the outcome of the study, an argument is advanced that current research findings provide bases for cultivar selection in antifungal effectivity as well as genetic variability of the cultivars. Allicin containing AGE can be used in specialized horticultural situations such as plastic tunnel and organic farming as a bio-stimulant to enhance cucumber growth and attenuate fungal degradation of agricultural produce.

Highlights

Plants and plant-derived produce are among the prime utilities of mankind for food, shelter and cure since the dawn of civilization and it wouldn’t be inappropriate to state that the use of medicinal plants predates written human history (Harrison et al, 2015)
Both the macrodilution and microdilution method revealed significant role of allicin as the prime antifungal substance in the aqueous garlic extracts (AGE) and the Minimum Inhibitory Concentration (MIC) range from 1 to 5% depending on the fungal strains and experimental procedures
Pure allicin Allicin aqueous standard (AAS) showed an MIC of 39–195 μg mL−1 allicin content which coincides with the amount of allicin observed in our AGE through HPLC analysis

Summary

Introduction

Plants and plant-derived produce are among the prime utilities of mankind for food, shelter and cure since the dawn of civilization and it wouldn’t be inappropriate to state that the use of medicinal plants predates written human history (Harrison et al, 2015). Garlic has been documented to possess antimicrobial (Feldberg et al, 1988; Ankri and Mirelman, 1999; Coppi et al, 2006; Ayazi, 2011; Wallock-Richards et al, 2014), anticancer (Thomson and Ali, 2003; Rana et al, 2011; Lee et al, 2013), antidiabetic (Lee et al, 2009), antiviral potential (Corzo-Martínez et al, 2007) and has ability to cope with cardiac complications (Lawson et al, 1992; Borek, 2001) Various organosulfur compounds such as DADS, DATS, DAS, Ajoene etc., have been suggested to contribute to the biological properties of garlic (Martins et al, 2016). To date, reports that document the genetic diversity in garlic cultivars of Chinese origin are few and far between

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