## 1 Introduction  
Garlic (_Allium sativum_ L.) is an edible plant which has been employed extensively as a spice since ancient times. The potential antimicrobial activities of garlic constituents have been investigated for a long time. [PERSON], for instance, investigated the antimicrobial potential of garlic. Organosulfur compounds, especially allicin, derived from garlic are excellent antimicrobial agents with a broad spectrum of biological activities against several bacteria (both Gram-positive and Gram-negative), fungi, protozoa and viruses [1; 2; 3; 4; 5]. Various studies have confirmed that thiol modification of glutathione and proteins is crucial for understanding the antimicrobial mode of action of allicin [6; 7; 8]. There are several mechanisms that contribute to the resistance to allicin in bacteria like the Mercuric reductase MerA proteins, which seem to be able to detoxify allicin by reduction. A genomic cluster conveying the resistance has been identified employing a highly allicin-resistant _Pseudomonas fluorescens_ strain isolated from garlic [9]. Recently, allicin, because of its oxidizing nature, has been reported to induce apoptosis in yeast cells [8], an alternative cell-killing mechanism to the formerly suggested specific oxidative inactivation of crucial enzymes [10; 11]. Allicin (diallythiosulfinate) is released when garlic cloves are crushed, and allin-an organosulfur precursor-is transformed into allicin via two step mechanism [8; 12; 13]. In the first step, allin is converted to allysulfenic acid and dehydroalanine by the enzyme alliinase. In the second step, allicin is synthesized from spontaneous condensation of two molecules of allysulfenic acid to form one molecule of allicin (Figure 1) [14]. The antimicrobial and pharmacological activities of garlic extract are predominantly derived from allicin [15]. The antimicrobial potency of garlic is quite amazing: a 50 g of garlic bulb can yield approximately 100 mg of allicin [16]. As far as the antimicrobial properties of allicin are concerned, it has been reported that allicin inhibits more than 300 microorganisms [17], including a variety of bacteria, such as, _Mycobacterium tuberculosis_, _Escherichia coli_, _Klebsiella proteus_, _Streptococcus_ spp., _Staphylococcus_ spp., _Bacillus_ spp., _Helicobacter pylori_ and even methicillin-resistant, _Staphylococcus aureus_ (MRSA) [15]. Similarly, the cytotoxicity of allicin in the form of vapors has also been evaluated in human lung pathogenic bacteria including multidrug resistant (MDR) bacterial strains [18]. The antimicrobial mode of action of allicin has been deciphered and DNA gyrase was confirmed to be the prime target of allicin in the antibacterial action [11]. Garlic extract has also shown promising antifungal activities against various pathogenic yeasts. The fungicidal activity of garlic was comparable to reference antimycotic drug, i.e., fluconazole [19; 15]. Similarly, garlic extracts have been reported to inhibit the growth of pathogenic fungi, such as _Botrytis cinerea_, _Penicillium expansum_, _Neofibraea alba_, _Fusarium_ and _Rhizopus_ species [20; 21]. The wide range of antifungal activities of allicin has also been confirmed against various plant-pathogenic fungi. Allicin exhibited promising antifungal activities both in vitro and in vivo against several plant-pathogenic fungi, e.g., _Alternaria brasiscicola_, _Botrytis cinerea_, _Magnaporthe grisea_ and _Plectospherella cucumerina_[22; 23; 24; 25]. There is a severe antibiotic crisis owing to the emergence of resistance leading to inefficacy of the currently available antimicrobials. Therefore, the development of novel potent agrochemicals is an alternative to combat resistance developed by phytopathogens [26; 25]. A large number of pests have developed resistance to the fungicides such as methyl bromide.