Etiology And Infection Characteristics Of Peanut Scab In Liaoning Province

Peanut(Arachis hypogara)is a kind of important industrial crop in China,it has been planting more than 400000 hm~2 in Liaoning province,become the third largest acreage crops.In recent years,peanut scab(Sphaceloma arachidis Bitaucourt et Jenkins)has been explosive popularity at Fuxin,Huludao and Jinzhou provinces,the loss was serious,and tends to gradually spread to the north.It has become one of the most serious diseases in peanut production in liaoning,restricted the healthy and sustainable development of the industry.Research that focused mainly on disease investigation,etiology,and chemical control of the disease but less on infection mechanism,epidemic regularity and forecasting technique can’t satisfy need for frontier plant protection.This study systematically researched on occurrence and damage in Liaoning Province,pathogen identification,morphology and molecular characteristics,the resistance identification and temporal dynamic of epidemic of peanut scab to provide theoretical basement for disease integrated control.1.Occurrence and etiology of peanut scab in Liaoning provinceIn order to definite the occurrence and harmfulness of peanut scab in Liaoning province,systematically investigate was carried out in peanut production areas.Result showed that peanut scab occurred and damaged in every main production area in Liaoning.Peanut scab occurred mainly in Fuxin,Huludao and Jinzhou,the average disease field rate were 100%,95%and 80%,the average strain rate were 96.34%,86.19%and 77.05%,the average disease index were 39.21,30.12 and 19.23.Sporadic disease were occurred in Shenyang and Tieling,the average disease field rate were 40%and 20%,the average disease index were less than 0.1.Based on the morphology and cultural characteristics,and multi-locus molecular analysis,the causal agent was identified as Sphacemola arachidis.Isolates were divided into 5 populations by RAPD and 0.79 coefficient and mainly grouped by location,their diversity was associated with geographical distribution.2.Resistance identification of peanut scab for different cultivated varietiesForty tested varieties differed significantly in disease resistance and 5 was HS(high sensitive),13 was S(sensitive),15 was MR(mid-resistance),7 was R(resistatance)while no HR(high resistance)or immune variety was detected.The main cultural variety Baisha 1016 in Liaoning province belong to high susceptible,and the disease index with 29.4 was the highest,Planted Baisha 1016 in large area was one of the main factors for peanut scab epidemic.3.The preliminary infections source and temporal dynamic of epidemic of peanut scabTo investigate the disease epidemic law in Liaoning Province,the field trial design was conducted to definite the preliminary infections source and temporal dynamic of epidemic of peanut scab.The results showed that pathogen of peanut scab overwinters in the form of mycelia and clamydospores in debris near the soil surface that became the main source for next year’s primary infection.The exponential phase began in late June to early July,logistic phase was in last ten-day period of July to last ten-day period of August,and terminal phase was in late August to the first ten-day period of September.Through comparing and analyzing the data,logistic model could well reflect the temporal dynamics of peanut scab.Baisha 1016 had the highest disease index,with an increase rate of 0.70 per day.Canopy temperature and humidity monitoring found that the occurrence of diseases with average temperature,accumulated temperature and moisture accumulation were significantly related.4.Infection characteristics of S.arachidisIn order to explore the mechanism and role of host defensive enzymes in plant-pathogen interaction,the infectious condition of S.arachidis and the dynamic changes of defense enzymes activity of pathogen infection in different resistance varieties of peanut were investigated in this study.The results showed that pathogen could infect leaf tissue though stoma and epidermis.At 25℃,Baisha 1016,the susceptible varity,of which the diseased plant rate was 80%,incubation period was 120h and disease index was 8.77 and those for Fuhua 17,the resistant varety,were 40%,144h and 2.77,respectively.At 15℃,incubation period of Baisha 1016 was 240h while no disease sympton was observed on Fuhua 17.Infection ability of fungi was obvious positive correlation with time in mosit chamber.The shortest time in moist chamber was about 4 h.The best combination of temperature and time in moist chamber for infection was 25～30℃ and 42～48 h.Culture time was significant positive correlation with infection ability of S.arachidis.With the prolonged culture time,the pathogen pathogenicity significantly decreased.The activities of defense enzymes including phenylalanine ammonia-lyase,peroxidase,polyphenol oxidase,superoxide dismutase and catalase in two peanut varieties all increased after inoculation and then dereased.Enzymes activities in resistant varieties(Fuhua 17)peaked at 24 to 36 hours post inoculation while in Baisha 1016 was at 48 to 72 hours post inoculation.The disease severity and infection index of Baisha 1016 were significantly higher than Fuhua 17 infected with S.arachidis.Mycelia began to expand 24h after inoculation and then expand through leaf epidermis 72h after inoculation.Conidiophores in brown was formed in the lesion area and produced ellipse conidia to complete infection circulation.