Studies On Plant Resistance Against Tomato Rhizoctonia Rot Induced By Beauveria Bassiana Colonization

Beauveria bassiana is an important entomogenous fungus,which exists widely in nature,can control many kinds of agricultural and forestry pests,and is widely used in the world.In recent studies,it has been found that B.bassiana could colonize in plants by different inoculation methods and gave a positive effect on plant growth and resistance against stress.However,there have been few reports on the application of B.bassiana to control soil-borne plant diseases.In the present study,1×10~8 spores/m L of B.bassiana was used for seeds soaking and root irrigation to Solanum lycopersicum,as well as a soil-borne phytopathogen R.solani was employed for study on biocontrol effects of B.bassiana as endogenesis against soil-borne phytopathogen.The growth promoting effect and disease resistance of tomato by B.bassiana colonization,and the colonization regulation of B.bassiana in tomato plants under pathogen infection were studied in greenhouse and field experiments,respectively.This study provided potential for plant soil-borne diseases control by B.bassiana.The main results of this study were as follows:1.Study on colonization characteristics of B.bassiana in tomato seeds and plants.B.bassiana could colonize in tomato seeds or plants by seed soaking and root irrigation.The spores of B.bassiana distributed in the seed coat and embryo of tomato seeds,and gradually germinated into hyphae over time after seed soaking by B.bassiana.The spores of B.bassiana could live in the root bark,the interior of the root,the stem bark and the leaf of tomato,and gradually germinated into hyphae after root irrigation by B.bassiana.In summary,B.bassiana could colonize,germinate and form hypha in tomato seeds and different plant parts by seed soaking or root irrigation.2.Effect of B.bassiana colonization on tomato growth.The different types of B.bassiana spores could promote the germination rate of tomato seeds and increase the root length,the B.bassiana blastspores showed better than the aerial conidia on that.The germination rate of tomato seeds increased by0.56%,83.33%and 66.67%on the 1st,2nd and 3rd day after the spore colonization of B.bassiana,respectively,and in which the root length of tomato increased by 95.58%,63.1%and 38.9%on the 3rd,4th and 5th day,respectively;While in the B.bassiana aerial conidia treatment group,the germination rate of tomato seeds increased by 0%,41.66%and 55%on the 1st,2nd and 3rd day,and the root length of tomato increased by 33.12%,17.17%and 17.48%on the 3rd,4th and 5th day,respectively.The spores of B.bassiana were colonized in tomato by root irrigation and seed soaking,both treatments were beneficial to the increase of plant height and chlorophyll content.On the 21st day after root irrigation.The plant height and chlorophyll content of tomato were increased by 14.19%and 3.23%,respectively,and which were 9.68%and 3.74%by seeds soaking,respectively.3.Study on resistance of tomato against R.solani infection by B.bassiana endophytic colonizationThe resistance of tomato plants to R.solani could be improved by both seed soaking and root irrigation assays,and the disease control effects of root irrigation method was better than that of the seed soaking.The disease incidence and disease index of tomato were reduced by 10%and 52.83%after seed soaking by B.bassiana respectively,and which were 22.37%and 27.54%after root irrigation respectively.In field experiments,compared with the treatment of pathogen naturally infection,the control effect of irrigating root treatment was 54.77%,and which was 62.40%by seeds soaking treatment;while in artificial inoculation treatment,which were 66.07%and 56.66%,respectively.4.Studies on the colonization of B.bassiana and pathogenic bacteria in tomato plants.Under the pathogen infection stress,the content of B.bassiana increased in the diseased parts of tomato plants,while where the content of pathogen decreased.In this study,relative real time quantitative RT-PCR(q PCR)was used to detect the fungal content in tomato samples.On the 21th day after pathogen inoculation,it showed that compared with the treatment of inoculation with R.solani only,the contents of pathogens in leaves and roots of tomato decreased by 54.9%and 78.8%after seed soaking by B.bassiana,respectively,and which were 64.7%and 75.9%after root irrigation by B.bassiana,respectively.Compared with the seed soaking treatment of B.bassiana.only,the content of B.bassiana in tomato leaves increased by 210.9%in treatment of inoculation with R.solani after seed soaking by B.bassiana on the 14th day,and which was 116.6%on the 21st day.Compared with the root irrigation treatment of B.bassiana only,the content of B.bassiana in tomato leaves increased by 102.7%on the 14th day and 68.9%on the 21st day in treatment of inoculation with R.solani after root irrigation by B.bassiana.The results indicated that B.bassiana could be recruited to the diseased area and inhibit the accumulation of R.solani.This study deepened the understanding of the interaction between B.bassiana and plants,and provided a theoretical basis for the rational use of entomogenous fungi to control soil-borne plant diseases.