Bioactivity Of Aqueous Garlic Extracts(AGE) In The Growth And Defense Responses Of Eggplant Against Verticillium Dahliae

Eggplant(Solanum melongena L.),an economically important vegetable crop in the world is often very susceptible to many biotic and abiotic stresses.Verticillium wilt,an important biotic stress caused by Verticillium dahliae severely affects eggplant at various growth stages.It's a potent soil-borne fungus that infects eggplant with prominent symptoms being leaf necrosis,wilted areas distinguished in yellow bronze coloration seen between leave veins,yield losses,stunted growth and vascular discoloration.The advanced infection due to Verticillium dahliae may sometimes lead to complete plant death.It infects the plant roots and proliferates as microsclerotia in soil that can survive for 14 years even in absence of host.Recently,due to harms and ineffectiveness posed by chemical pesticide application for verticillium wilts,horticultural practices are favored among the scientific community.The antimicrobial potential of garlic derived compounds has already been proven,what's new in this aspect is to derive its effectivity towards more meaningful applications at the field levels such as its growth promoting potential and more possibly its use as elicitor for defense against microbial infection.The current study was therefore designed to investigates the aqueous garlic extract as biostimulator or inducer in growth and defense mechanism of eggplant against V.dahliae.The thesis comprises the following studies:1.Foliar spraying of AGE promotes growth,physiology and yield of eggplants in plastic tunnel conditionsRecently,botanical extracts are gaining popularity as biostimulants in vegetable production.In present study,the effect of AGE was studied on the growth and physiology of eggplant grown in plastic tunnel.AGE was foliage sprayed with various frequencies,i.e.,0,S1(once),S2(twice)and S3(thrice)at two independent growth stages,pre-and post-transplant.The results showed that the treated plants exhibited stimulatory responses in growth and physiology in accord with the repetition of AGE spray and growth stages of the plants,respectively.A single foliage sprayed pre-transplant resulted in improved growth,i.e.,plant morphology and biomass,and enhanced antioxidants enzymes(superoxide dismutase,SOD;peroxidase,POD),photosynthesis and chlorophyll abundance observed at vegetative,first flowering and fruit setting stages,respectively.However,thrice application inhibited the plant growth and development and resulted in lipid peroxidation,i.e.,increased malondialdehyde(MDA)content.In addition,the post-transplant application also showed growth stimulation and interestingly,an overall positive influence was observed with respect to the AGE application and no significant increase in the MDA content indicated the post-transplant seedlings responded well.Our findings demonstrate that AGE can act as a biostimulant to enhance the eggplant growth in plastic tunnel production.2.Seed priming with AGE enhances germination efficiency,alters antioxidant enzymes,modulates ROS and improves early seedling developmentOur previous studies have shown that foliar spray and root fertigation with AGE improve plant growth and physiology in pepper,eggplant,tomato and cucumber.Current study was aimed to evaluate the seed priming potential of AGE to enhance seed germination and early seedling growth of eggplant.Different concentrations(100,200 and 300?g m L^-1)of AGE were evaluated along with methyl jasmonate(Me JA)and salicylic acid(SA),plant growth regulators with reported seed priming potential whereas,water was taken as a control treatment.Eggplant seeds were primed for 4-,8-and 12-hours and seed germination traits such germination rate index,germination percentage,mean germination time,and early seedling growth traits such as fresh and dry weights,root and shoot lengths were observed.Moreover,plant antioxidant enzymes activities and lipid peroxidation levels,soluble protein contents and reactive oxygen species were monitored to establish the stimulatory/inhibitory effects of the treatments.The results indicate priming potential of AGE,SA and Me JA to enhance seed germination and early seedling growth in eggplant and the effects were obvious in various morphological and physiological traits.Seed priming significantly altered the antioxidant enzymes activities such as superoxide dismutase(SOD),and peroxidase(POD)with alteration in the reactive oxygen species(ROS).Interestingly,priming duration also affected the bioactivity of these chemicals because seed priming with 300?g m L^-1 AGE for 4 hours had a positive influence,however,prolonged exposure to the same concentration inhibited the seed germination process and induced oxidative stress on the seedlings with elevated levels of MDA content.We propose AGE seed priming as a biostimulant to enhance seed germination and early seedling growth in eggplant and the results hence lay the foundation for the preparation of garlic-based compounds to improve vegetable production under plastic tunnels and greenhouse.3.Aqueous garlic extract and diallyl disulfide application promote eggplant growth,elevate physiology and prime the defense responses to resist Verticillium dahliae infectionAGE and garlic allelochemical diallyl disulfide(DADS)have been recently reported to bear bioactive properties to stimulate plant growth and development and alter defense-related physiology.We,therefore,performed individual bioassays to study these chemicals as possible biostimulants for defense mechanism against Verticillium dahliae in eggplant seedlings.AGE and DADS were applied individually as foliar or root fertigation to the eggplants and samples were collected before and after pathogen inoculation at various intervals to indicate the defense mechanism.The obtained data revealed that with the application of AGE and DADS,the seedlings showed a primed state of defense responses including antioxidant enzymes activation,chlorophyll contents abundance and altered photosynthesis system compared to the control plants.Furthermore,the microscopic analysis of the plants showed a significant difference in the disease development and the level of pathogenesis was considerably low in the AGE or DADS treated plants in comparison to the control plants.The low abundance of ROS was noticed which clearly indicated that the plants were able to successfully encounter pathogen attack.The treated plants exhibited lower disease incident and disease severity index indicating successful defense against verticillium infection.Our results are therefore among the first to address the biostimulatory effects of AGE or DADS to induce resistance in eggplant seedlings against V.dahliae and may be used to establish preparation for garlic-derived bioactive compounds to improve growth and defense responses of eggplants under protected horticultural situations such as glasshouse or plastic tunnels system.