Isolation And Characterization Of Antagonistic Fungi Against Five Fungal Phytopathogens

The demand for quality food,feed,and fiber continue to surge as a result of the rising global population which subsequently increases the threats plant diseases pose on crops worldwide.Over the past years,farmers have adopted the use of agrochemicals to control plant diseases but the environmental pollution and changes to soil microbial biodiversity by such chemicals continue to remain a global challenge.As a result,ecologically friendly and safe methods to control plant diseases are required which has paved way for research into Biological Control Agents(BCAs).Nonetheless,for the successful implementation and use of biological organisms as control agents,an in-depth understanding of their underlying mechanism is needed.In view of this,different fungi were isolated from the tea plant rhizosphere and screened for several isolates with high antagonistic activity against all five selected phytopathogens;Athelia rolfsii DQ,Fusarium oxysporum FS,Glomerella cingulata PTT,Colletotrichum gloeosporiodes CMT,and Botrytis cinerea Pers PTM.Seventy(70)different fungal isolates were isolated from the tea rhizosphere with different antagonistic activity on the selected phytopathogens.15 isolates with good antagonistic activity on all the phytopathogens were selected for identification and further studies.Most of these potential antagonists belonged to the genera Trichoderma hence,Mucor moelleri AA1 together with two randomly selected Trichoderma species(T.koningiopsis AA4 and T.asperellum MK6)were selected for this study with most attention on the M.moelleri.The results showed that M.moelleri had high antagonistic activity against all five phytopathogens just as that of the Trichoderma test species using both in-vitro and in-vivo techniques.It was evident that M.moelleri controlled the growth of the pathogens in both dual culture and liquid co-culture.Furthermore,a pot culture study revealed simultaneous disease suppression and plant growth promotion by the antagonist.A growth curve analysis of the M.moelleri and the individual phytopathogens revealed the fast growth of the antagonist as opposed to the pathogens.Nonetheless,M.moelleri recorded a considerable amount of mycelial growth even at 12hr whereas the pathogens recorded mycelial growth after 24-36hr.Again,using the sandwich plate method,it was observed that M.moelleri produced microbial volatile compounds(mVOCs)that as well inhibited pathogen growth.More so,there was the production of several hydrolytic and oxidative enzymes such as β1,3-glucanase,catalase,and proteases in equally high content as that of the Trichoderma sp.To further understand the underlying mechanisms,scanning electron microscopy(SEM)and headspace-solid phase microextraction(HS-SPME)was employed.Examining the interaction site of the dual culture of M.moelleri and the individual phytopathogens using SEM,different forms of activity were observed.The main forms being:the antagonist grabbing the pathogen,hooking of the pathogen,decrease in mycelial size and the production of web-like structures by the pathogen.The HS-SPME analysis of the antagonists identified several mVOCs which constituted compounds of various chemical groups such as alkaloids,esters,ether,monoterpenoids,alcohol,aromatic compounds,amide,heterocycles,acyclic hydrocarbons,carboxylic acids,etc.M.moelleri not only suppressed pathogen growth but also promoted plant growth and development by the production of indole-3-acetic acid(IAA),and ACC deaminase.Overall,these results combine to make M.moelleri a good prospective candidate for biological control and as a plant growth-promoting agent.The present study appears to be the first report identifying M.moelleri as a biological control agent.