Diversity And Ecological Distribution Of Endophytic And Entomogenous Fungi In Cruciferous Habitats

Cruciferous vegetables are important economic crops and play an important role in agriculture and human diets.The long-term and large-scale use of pesticides has led to resistant pest populations,which has seriously restricted the production and development of vegetables.Biological control,as an alternative strategy to chemical control,has been widely accepted worldwide.However,microbial control,as an important biological control strategy is still not widely applied.Fungi are widely distributed in nature.Both endophytic fungi and entomogenous fungi can be used as biocontrol agents in agriculture to assist plants to resist insect pests and diseases,and have broad application potential.To make a better use of the biocontrol potential of fungi,we first need to know their occurrence in nature.Three cruciferous plant species,Chinese cabbage(Brassica rapa),radish(Raphanus sativus)and white cabbage(Brassica olerocea),cadavers of 4 major cruciferous pests,diamondback moth(Plutella xylostella),flea beetle(Phyllotreta striolata),beet armyworm(Spodoptera exigua)and leaf miner(Liriomyza sp.),and soil samples were collected from 21 focal cruciferous fields with different landscape contexts and farming practice during four seasons(summer,autumn,winter and spring).Endophytic and entomogenous fungi were isolated,cultured,identified and evaluated for their association between fungal community diversity with factors namely landscape composition,host plant,farming practice,season and elevation,and tested for their pathogenicity to diamondback moth.The main results are summarized as follows:(1)Plant identity,plant part and season influenced the fungal endophyte community diversity in crucifers.Endophytic fungal isolates(4,178),belonging to 2 phyla,6 classes,16 orders,30 families,51 genera and 110 species were collected.Plant identity significantly influenced the occurrence and abundance of endophytic fungi,but had no significant influence on the diversity indices.The community diversity in roots was significantly lower than those of stems and leaves.The community diversity varied dynamically among seasons.Spring and autumn were more suitable for the growth of endophytic fungi and their community diversities were higher than those in summer and winter.The application of chemical pesticides on conventional farms significantly inhibited the endophytic diversity in roots,but there was no significant difference in roots,stems and leaves in organic farms.Factors were associated with specific endophytic fungal orders.For example,fungi within the Hypocreales,Eurotiales and Sordariales were associated with plant roots,while those within Capnodiales,Pleosporales and Trichosphaeriales were associated with spring.Similarly,factors were associated with specific functional traits.For example,pathotroph,symbiotroph,dung saprotroph,endophyte,epiphyte and plant pathogen were positively associated with autumn and summer seasons,white cabbage,leaf tissues and elevation,while saprotroph,animal pathogen,fungal parasite,undefined saprotroph,wood saprotroph and yeast-like organisms were positively associated with spring and winter seasons,root tissues,grassland and water in the landscape.(2)Elevation was a factor in shaping the community of entomogenous fungi in cruciferous vegetables.Entomogenous fungal isolates(240),belonging to 3 classes,7 orders,14 families,23 genera and 49 species were collected.Various factors influenced the community composition of entomogenous fungi.For example,Fusarium dominated in summer and autumn,Cladosporium in spring,and Aspergillus in winter.The diversity of entomogenous fungal communities in high-elevation farms was significantly higher than that in low-elevation farms.The abundance of entomogenous fungi isolated from larvae was significantly higher than that of adults.However,the insect life stage had no significant influence on the diversity and evenness of the entomogenous fungal communities.Farming practice,plant identity,season and insect species had no significant influence on the diversity of entomogenous fungal communities.Canonical correlation analysis showed that factors were associated with specific entomogenous fungal genera.For example,Phoma was associated with Chinese mustard and leaf miner larvae;Gibberella,Fusarium,Trichoderma and Aspergillus were associated with white cabbage,beet worm larva,forest and unused land in the landscape.(3)Farming practice and elevation influenced the soil-borne entomogenous community diversity.Soil-borne entomogenous fungi(244),belonging to 3 classes,3 orders,8 families,12 genera and 16 species were collected.Factors had little effect on the community composition of soilborne entomogenous fungi and Metarhizium pingshaense was the most dominant species.Farming practice had significant influence on the occurrence and abundance of soil-borne entomogenous fungi.The occurrence and abundance of soil-borne entomogenous fungi was significantly lower in traditional farms using pesticides than in organic farms.Similarly,elevation significantly influenced the abundance of soil-borne entomogenous fungi.Soil-borne entomogenous fungi in high-elevation farms were significantly higher than those in low-elevation farms.However,plant identity,farming practice and elevation had no significant influence on the community diversity indices of soil-borne entomogenous fungi.Two isolates were more pathogenic to diamondback moth than others.One was GZ-4-8-b(Penicillium janthinellum),causing 66% mortality,and the other was GZ-4-8-a(M.pinghaense),causing 52% mortality.In summary,endophytic fungi in cruciferous vegetables were influenced by seasonal changes and hosts.Farming practice mainly influenced the occurrence of endophytic fungi in plant roots and entomogenous fungi in soil,indicating that application of chemical pesticides could reduce soil microbial diversity.Semi-natural habitats were closely related to the occurrence of endophytic and entomogenous fungi.