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

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.

Transcriptomic insights into the allelopathic effects of the garlic allelochemical diallyl disulfide on tomato roots

“…Hayat et al . showed that aqueous garlic extract altered the defense mechanism of cucumber seedlings through the activation of ROS at mild concentrations29. However, in the present study, the ROS content may decrease in response to the down-regulation of the RBOH genes involved in ROS production (Supplementary Table S6), suggesting that ROS may not be the active signal in inducing tomato resistance under 0.21 mM DADS conditions.…”

“…(2013) showed that the activities of CAT and POD in pepper were significantly enhanced when intercropping with garlic, while that of PPO was inhibited7. In addition, the activities of SOD, POD and CAT in cucumber ( Cucumis sativus ) leaves were also increased in response to aqueous garlic extracts at proper concentrations29. Wang et al .…”

Aqueous Garlic Extract as a Plant Biostimulant Enhances Physiology, Improves Crop Quality and Metabolite Abundance, and Primes the Defense Responses of Receiver Plants

“…Garlic cultivar G025 was obtained from the garlic germplasm unit, College of Horticulture, Northwest A&F University, China. The aqueous extract was prepared according to method previously described in our article [27]. Due modifications were made, however, according to the requirements of experiment.…”

“…However, less is understood about the possible biological activity of garlic-derived compounds on the growth and physiology of receiver plants, particularly their utility as growth promotors, or about priming inducer/stimulator needs. In our earlier studies, aqueous garlic extract (AGE) has been shown to alter the antioxidative response of cucumber seedlings, and this effect was observed to be concentration-dependent [27]. Moreover, tomato seedlings' growth in response to variable concentrations of AGE revealed significant results [28].…”

Is Alpha-Glucosidase Inhibition a Mechanism of the Antidiabetic Action of Garlic (<i>Allium sativum</i>)?

“…Many studies have found that garlic has strong antioxidant properties. It has also been found that raw garlic has more antioxidant activity than cooked garlic [29]. Anti-inflammatory and immune protection effects of garlic have also been demonstrated [30].…”