Resistance Identification Of Peanut Germplasm From Henan Province To Aspergillus Flavus And Analysis Of Resistance Related PAL Gene Family

Peanut(Arachis hypogaea L.)is important economic and oil crops in China,and it is a great vegetarian source of protein and healthy fats.It has high nutritional value and varieties of therapeutic functions.China is the largest peanuts producer,whose annual planting area is only smaller than India,ranking second in the world,and its total output ranking first in the world.However,peanut is one of the most susceptible crops to be contaminated by aflatoxin.The contamination process can occur in growth,harvesting,storage and transportation,etc.Aflatoxin contamination seriously endangers the development of the peanut industry and human health.Screening the resistance of peanut germplasm will lay the foundation for the research of the resistance mechanism of peanut to Aspergillus flavus infection.In this study,66 peanut germplams in Henan Province were tested for resistance to Aspergillus flavus infection and then determinate its aflatoxin content.Four materials with different resistances to Aspergillus flavus infection were used to detected and analysis of defense-related enzyme activities such as phenylalanine ammonia lyase,peroxidase,and polyphenol oxidase.In addition,the cultivated peanut PAL gene family was took as an example to analyze the role of PAL in peanut resistance to Aspergillus flavus infection.The main conclusions are as follows:1.This study identified the resistance to Aspergillus flavus infection of 66 peanut germplasms include landrace and from released variety Henan Province.The result indicates that have no peanut variety of these germplasm is immune completely to infection of Aspergillus flavus.There are 5 varieties that are moderately resistant to Aspergillus flavus infection,accounting for 7.58 %;there are 32 materials that are moderately susceptible to Aspergillus flavus infection,accounting for 48.48 %,and21 materials are susceptible to Aspergillus flavus infection,accounting for 19.4 %;8materials were highly susceptible to Aspergillus flavus infection,accounting for12.12 %.The result indicated that have no peanut variety of these germplasm is immune completely to infection of Aspergillus flavus.The result of aflatoxin contenet showed that 8710-0-0-4 had the lowest aflatoxin content,which was 11.41 ppm.Correlation index of infection index and AFB1 content was 0.60,which indicate these two characters were weak correlation.2.In this study,four peanut varieties with different resistance to Aspergillus flavus infection were selected as materials to perform a comparative test of infection of Aspergillus flavus on seeds with intact seed coats and seeds without seed coats.The difference of peanut between resistant with susceptible varieties with intact seed coats is obvious,and the peanut seeds with the seed coat removed are all covered by Aspergillus flavus spores and there is no difference between resistant with susceptible materials.This result indicated that peanut seed coats play an important role in resisting to the Aspergillus flavus infection.In addition,the comparative test of the three defense enzyme activities,phenylalanine ammonia lyase,peroxidase and polyphenol oxidase,showed that the PAL and PPO of resistant materials and susceptible materials are significantly different after being infected by Aspergillus flavus in enzyme activity changes,especially PAL,the time to reach the peak of resistant varieties is 2 days earlier than that of susceptible varieties.The difference in changes enzyme activity were still exsist in the seeds without coat and it happened earlier than that when the seed coat is intact.3.In order to further identify the role of peanut PAL gene family in peanut resistance to Aspergillus flavus infection,the Ah PAL gene family was systematically analyzed.In this study,total of 10 PAL genes were identified in the cultivated peanut genome database.The PAL protein in A.thaliana,A.hypogaea,two wild peanuts(A.duranensis and A.ipaensis),M.truncatula,G.max and C.cajan were used to construct a phylogenetic tree and it was found that the PAL gene family of legumes can be divided into three groups.The PAL of each cultivated peanut can find orthologous genes in the wild species,and the Ka/Ks value of the gene pair is far less than 1,indicating that these genes were under the strong purification selection during the evolution process.After being infected by Aspergillus flavus,expression of some Ah PAL genes were changed,indicating that it may play a role in resistance to Aspergillus flavus infection.