Study On Physiological And Biochemical Resistance Of Peanut (Arachis Hypogaea L.) Against Web Blotch

Peanut(Arachis hypogaea L.)is an important oil crop in the world.Peanut web blotch is a leaf disease of peanut,which can cause reduction of 10% to 20% peanut yields,and in serious cases up to 40% yield losses.Web blotch has become one of the major threats restricting the production of peanuts in the main production areas in China.Peanut varieties harboring web blotch resistances are considered to be the most economical and effective way to reduce the damage from biotic stress.However,the mechanism of resistances against peanut web blotch is still unclear,which restricts the breeding process of resistance to peanut web blotch.Firstly,this study established a rapid method to obtain a large number of conidia of the pathogen caused peanut web blotch,improved the method of conidia inoculation and evaluated the different resistant levels of six peanut varieties.Furthermore,by inoculation of the pathogen on different peanut varieties,the infection process of the pathogen and different levels of hypersensitive response besides the change of plant defense related enzyme activity from the above mentioned peanuts varities were analyzed.The main results are listed as follows:1.Pathogen was isolated from peanut leaf tissue collected from the experimental field of Riverside Base of Henan Academy of Agricultural Sciences.By observing the colonial morphology,sporozoites and conidia on PDA and OA growing media,in addition to analyzing rDNA-ITS sequence,which showed 100% homology with Peyronellaea arachidicola sequence,we confirmed that the isolated fungal pathogen was the same species that previously reported cause of peanut web blotch disease(P.arachidicola).The sporulation of mycelia and conidia under light-dark alternation(12 h/12 h and 16 h/8 h)and dark culture were compared.It was found that mycelium inoculation and conidia inoculation produced the most spores under light-dark alternation(16 h/8 h),pycnidium can be obtained rapidly and in large quantities by conidial inoculation,which was more than six times of that under other culture conditions2.Peanut varieties showing different resistant levels against web blotch were inoculated with mycelium suspension and conidia suspension.After 12 days,different peanut varieties were identified by leaf area analysis system and nine-grade indoor standard for peanut web blotch.Our results showed that: 1)The Disease index for different peanut varieties by these two methods were identical.The resistance responses ranged from high to low was WBR1/WBR2,WBR3,WBS1,WBS2 and WBS3.However,the concentration of mycelial in the inoculation suspension is hardly controlled with the mycelial method,and the coefficient of variation between repetitions showed much higher than that of spore suspension.2)By analyzing the lesion area and disease index of six varieties inoculated with conidia suspension of different concentration,it was found that the lesion area and disease index of all varieties(except WBR1 and WBR2)were significantly different under different inoculation concentration,but there was no significant difference between repetitions.With the increase of inoculation concentration,the lesion area and disease index increased,and the resistance was consistent with the tested inoculaum concentration.These results indicated that spore suspension inoculation had high homogeneity and stability which could accurately identify disease resistance levels of peanut varieties.3.Observing the infection process of web blotch pathogen by optical microscope.It was found that conidia produced primary haustorium(or appressorium)on different resistant levels of peanut,but the hypersensitive responses were different.The range and degree of hypersensitive response about resistant varieties were larger and faster,and the occurrence time of hypersensitive responses were earlier than that of susceptible varieties.The number of different infection structures in leaf tissues of different varieties increased significantly with the prolongation of inoculation time,and the number of hypersensitive response was positively correlated with disease index,while the number of collateral mycelium and primary haustorium(or primary appressorium)was negatively correlated with disease index of peanut varieties.4.Physiological and biochemical techniques were used to study the relationship between the activities of defensive enzymes and resistant reponses.Our results showed that the activities of SOD,POD and CAT in leaves of resistant and susceptible varities were increased.However,the activities of three enzymes in resistant cultivars were significantly higher than those in susceptible cultivars,and the peak time of CAT activity in resistant varieties(48 h)was earlier than that in susceptible varieties(72 h).