Font Size: a A A

Impact Of Pathogenic Fungal Sclerotia On Soil Microbial Diversity

Posted on:2020-07-06Degree:DoctorType:Dissertation
Country:ChinaCandidate:Mehmood Mirza AbidFull Text:PDF
GTID:1360330611482949Subject:Molecular Plant Pathology
Abstract/Summary:PDF Full Text Request
Sclerotia of various fungi are successful survival structures that remain viable within the soil for a long time under unfavorable conditions.Sclerotia are rich sources of chitin,carbohydrates,proteins,dietary fibers,fats and minerals,notably Na,K,Ca and Mg.It is a well-known fact that sclerotia are potential candidates for various purposes,including a nutritional source for microbial growth after parasitized by biocontrol agents.Rhizoctonia solani Kühan and Sclerotinia sclerotiorum(Lib.)de Bary,notorious soil-borne pathogens of various important crops,produce numerous sclerotia to oversummer and/or overwinter in the soil.Considering the coexistence of the sclerotia and other microbes in the soil,we hypothesized that sclerotia in soil may affect the community of soil microbes directly and/or indirectly.Hence,we inoculated sclerotia of R.solani and S.sclerotiorum in the soil collected from the rice-rapeseed rotation field and S.sclerotiorum in the soil collected from rapeseed-fallow rotation field in Shayang County,Hubei Province to observe changes in microbial diversity over three months using 16 S r RNA and ITS2 sequencing techniques.Soil samples were inoculated with sclerotia of R.solani or S.sclerotiorum and were incubated at 28±2? for three months and soil moisture content during the experimental period was retained 60-80% water-filled pore space(WFPS).The experiments were carried out in three biological replicates and soil samples were collected with a 1-month interval until the 3rd month and subjected to sequencing.In part 1,rice-rapeseed soil samples were inoculated with sclerotia of R.solani at concentrations of 0.50-2.50 g/ 100 g to find out the effect of inoculum concentration on soil microbial diversity.We observed a clear difference in diversity estimates of microbial communities in soil samples amended with 2.50 g sclerotia compared with the other concentrations.Plant growth-promoting bacteria(PGPB)such as Chitinophaga,Flavisolibacter,Dyella and biocontrol agents(BCA),notably Kribbella,etc.showed enrichment in amended samples.Moreover,microbes involved in different processes of the nitrogen cycle especially Azotobacter,Anaeromyxobacter,Geobacter,Thiobacillus,Nitrospira,and Nitrosospira,etc.revealed enhanced abundance in sclerotia-amended samples.Furthermore,beneficial fungal genera i.e.Ascobolus,Stachybotrys,Trichoderma,Lecanicillium,and Vermispora,etc.exhibited enhancement in sclerotia-amended soil samples compared with non-amended samples.Whereas,pathogenic fungal genera e.g.Fusarium,Cladosporium,Botrytis,Rhizopus,and Thanatephorus itself depicted more abundance in amended samples compared with non-amended controls.Conclusively,soil samples amended with 2.50 g sclerotia showed a diverse microbial population and activated more beneficial and pathogenic microbes.Hence,the 2.50 g sclerotial concentration was selected for subsequent experiments.In part 2,rice-rapeseed field soil stored for 1 year at room temperature was amended with 2.50 g R.solani sclerotia incubated for three months as described earlier and termed as2nd-year samples.Whereas,the soil samples amended with 2.50 g of R.solani sclerotia from Part 1 were used for comparison and termed as 1st-year samples.The objective of this part was to check the influence of soil storage on microbial diversity.It has been observed that samples of the 1st-year depicted higher diversity compared with the 2nd-year.We found that Azotobacter,Bradyrhizobium,Lysobacter,Ohtaekwangia,Phaselicystis,Parasegetibacter,Terrabacter,exhibited enhancement only in the 1st-year amended soil samples while Massilia and Phenylobacterium were solely enriched in the 2nd-year amended samples.In contrast,Typhula,Volutella,and Lecanicillium were solely abundant in the amended samples of 1st-year whereas Rhizopus,Chaetomium,Trichocladium,Curvularia,and Aspergillus revealed enhanced abundance only in the 2nd-year amended samples.It is worth mentioning that most of the above-mentioned fungal genera are reported plant pathogens.Furthermore,Chaetomium and Rhizopus exhibited abundance only in non-amended samples of 1st-year but showed enhancement in sclerotia-amended samples of 2nd-year while Chrysosporium,Cladorrhinum,Arthrobotrys depicted enrichment in 2nd-year amended samples.This comparative study revealed that soil samples stored for 1 year resulted in the decreased microbial abundance as well as activated more pathogenic fungal genera compared with 1styear amended samples,which might be due to R.solani or due to the storage of soil.In part 3,keeping in view the rapeseed rotation in rice-rapeseed soil and to find out the reason for a change in microbial diversity and/ or abundance due to the amendment of R.solani sclerotia in 2nd-year soil,we amended 2.50 g sclerotia of S.sclerotiorum in 2nd-year rice-rapeseed soil.We found that alpha diversity indices confirmed the decline in the fungalcommunities while enrichment of bacterial communities was evident within amended soil samples compared to the non-amended controls.Sclerotial presence enhanced the abundance of PGPB,such as Chitinophaga,Anaeromyxobacter,Azoarcus,etc.whereas,some PGPB and BCA declined within the amended soil such as Sphingomonas,Massilia,Flavisolibacter,etc.In the amended soil,enrichment of antagonists like Clonostachys,Trichoderma,Arthrobotrys,and Vermispora,etc.was evident.While the growth of several genera with reported pathogenic potential such as Chaetomium,Cladosporium,Diaporthe and Sclerotinia revealed restricted abundance in amended samples but Fusarium was enriched in amended samples.This study provided evidence that most of the beneficial microbes revealed enrichment in S.sclerotiorum sclerotia amended soil samples.Besides this,we can envisage that storage of soil is not the influencing factor for the enrichment of pathogenic microbial population but it was R.solani which was the main cause of their enhanced abundance.In part 4,to further confirm the findings where soil samples amended with R.solani and S.sclerotiorum in 2nd-year of Part 2 and Part 3 depicted enrichment of varied population,we used the sequenced data of non-amended,R.solani and S.sclerotiorum amended soil samples from Part 2 and Part 3 and analyzed it again.This study exhibited that alpha diversity of bacterial communities revealed higher diversity in the S.sclerotiorum sclerotiaamended soil samples while fungal communities were more diverse in the non-amended samples.The bacterial genera having beneficial potential related to plant and its ecological niche,notably Rhizomicrobium,Dyella,Ochrobactrum,Rhodanobacter,Opitutus,Achromobacter,and Nitrosospira,etc.were evidently abundant in R.solani sclerotiaamended soil samples.Similarly,Geobacter,Anaeromyxobacter,Nitrospira,Phenylobacterium,and Burkholderia,etc.represented enhanced abundance in S.sclerotiorum sclerotia-amended samples.Comparatively,Aspergillus,Chaetomium,Curvularia,and Thanatephorus,etc.depicted enrichment only in R.solani sclerotia-amended samples while Arthrobotrys,Ascobolus,Vermispora,Clonostachys,and Mortierella,etc.showed enhancement only in S.sclerotiorum sclerotia-amended samples.Whereas,Alternaria,Fusarium,Diaporthe,Sclerotinia etc.were abundant in non-amended soil samples.It is imperative to mention that S.sclerotiorum sclerotia-amended samples enriched microbes were mostly of beneficial importance compared with R.solani sclerotia-amendedsamples where most of the enriched ones were of pathogenic nature.This comparative analysis provided further evidence that non-amended and R.solani amended soil samples enriched the pathogenic fungal genera whereas,S.sclerotiorum-amended samples favored the beneficial ones.In part 5,to mimic oversummer state of S.sclerotiorum sclerotia in the soil collected from the rapeseed-fallow field,we amended 2.50 g of S.sclerotiorum sclerotia to investigate the periodic shift in microbial diversity with a special focus on the abundance of soil-borne plant pathogens as well as PGPB.We found that microbial communities declined within sclerotia-amended soil samples compared with non-amended samples.S.sclerotiorum sclerotia enhanced the abundance of PGPB,such as Rhizobium,Mesorhizobium,and Burkholderia etc.Moreover,enrichment of fungal antagonists like Clonostachys,Trichoderma,Talaromyces,etc.was conspicuous in amended samples.In contrast,the presence of sclerotia resulted in the growth restriction of several reported plant pathogenic fungi belonging to various genera such as Athelia,Alternaria,Colletotrichum,Aspergillus,Sclerotinia and Macrophomina etc.It was evident that abundance of Sclerotinia declined in amended samples after 1st month along with Fusarium and Botrytis but Rhizopus was abundant even after the decline of aforementioned fungal genera.It can be concluded that Sclerotinia amended samples favored the growth of many beneficial bacterial and fungal genera along with few pathogenic ones where the latter declined along with Sclerotinia except Rhizopus.Conclusively,this study revealed astonishing results that the amendment of R.solani sclerotia enhanced the bacterial genera with reported beneficial potential as well as increased the abundance of several notorious fungal pathogenic genera.In contrast,S.sclerotiorum sclerotia-amended soil samples enhanced the abundance of beneficial bacterial and fungal genera but restricted the growth of pathogenic fungal genera.Moreover,the abundance of S.sclerotiorum declined considerably compared with R.solani that showed enhancement during different months of study in different experiments within sclerotia-amended soil samples.It might be due to the non-establishment of a beneficial consortium of biocontrol agents which was observed in the case of S.sclerotiorum.Moreover,these findings provided evidence that the addition of pathogenic fungal sclerotia enhanced the abundance of bacterialgenera with beneficial potential and suppress the plant pathogenic fungi,which might be due to the enrichment of reported biocontrol agents.Thus,we conclude that germination of sclerotia in the soil can influence the diversity of soil microbes,including enriching beneficial microbes and suppressing plant pathogens(especially in soil samples amended with S.sclerotiorum sclerotia).Whereas,the R.solani sclerotia-amended samples enriched the beneficial microbes as well as plant pathogens.
Keywords/Search Tags:Sclerotia, Rhizoctonia solani, Sclerotinia sclerotiorum, microbiome, plant growth-promoting bacteria, biocontrol agents, enrichment, microbial consortium
PDF Full Text Request
Related items