Study On Gray Leaf Spot Of Maize Caused By Cercospora Zeina

Maize(Zea mays L)is one of the most important cereal crops in the world.It is also known as the world's major food crops along with wheat and rice.It is not only a human staple food but also an important raw material of feed,light industry and medicine industry,and plays an important role in the development of national economy.Gray leaf spot of maize is a serious foliar disease of Zea mays in many countries where it is cultivated and can cause heavy yield loss.At present,it has become one of the most important diseases of maize in china.In 1991,maize gray leaf spot caused by Cercospora zeae-maydis was found in Dandong,China,it is the first occurrence in China.For a long time,the domestic researchers all believe that only C.zeae-maydis is the pathogen of maize gray leaf spot in China.But in 2010,I found the maize gray leaf spot caused by C.zeina occurred in Yunnan,China.It has caused serious yield losses in Yunnan and has a tendency to spread to northern China.However,there is no report on the systematic research for the disease in the world.Its occurrence regularity is not clear and the effective prevention and control measures are unknown.So it has the probability of outbreak.Therefore,using the methods of plant pathology and molecular biology,I study the disease symptoms,etiology,diagnosis,distribution,pathogen pathogenicity,resistance of germplasms,host resistance mechanism and resistance QTL mapping for this disease,in order to provide scientific basis for the diagnosis,monitoring,early warning,effective prevention and control of the disease.The main results are as follows:1.The occurrence of maize gray leaf spot caused by C.zeina in China was first reported.From 2010 to 2011,I investigated the severity of maize gray leaf spot in Yunnan and observed the characteristics of disease symptoms.Samples were collected from Dali,Dehong,and Baoshan of Yunnan.Pathogen was isolated by single spore isolation.Morphological identification,specific primer and rDNA-ITS sequence analysis was performed.The results showed that the maize gray leaf spot in Yunnan was a new maize disease,and the casual agent was C.zeina.2.The differences in biological characteristics of C.zeina and C.zeae-maydis were studied clearly.The comparative analysis of biological characteristics of C.zeina and C zeae-maydis was performed.The results showed that there were significant differences in the optimum medium,carbon source,nitrogen source,temperature,and the suitable temperature and pH for conidia germination of C.zeina and C.zeae-maydis.It showed that there were significant differences in the biological characteristics of the two species of Cercospora.3.The species and geographical distribution of pathogen of maize gray leaf spot in China were studied clearly.From 2010 to 2016,using the methods of plant pathology and molecular biology,the strains were detected and analyzed that were isolated from samples collected from 97 cities(counties)of 13 provinces in China.The results showed the pathogens of maize gray leaf spot were C.zeina and C.zeae-maydis.The C.zeae-maydis distribute in Heilongjiang,Jilin,Liaoning,Neimenggu,Shanxi,Shandong,Shanxi,Henan,Sichuan,Hubei,and Hunan.The C.zeina distribute in Yunnan,Guizhou,Sichuan,Hunan,Hubei,Shanxi and Henan,and it has a tendency to spread to northern China.4.Evaluation of 300 maize germplasms for resistance to C.zeina and C.zeae-maydis were performed.A technique of artificial inoculation for resistance evaluation to C.zeina was established.Using this technique,resistance of 300 maize germplasms to C.zeina and C.zeae-maydis was evaluated.The results showed that 10,100,121,62 and 7 maize germplasms were highly resistant,resistant,moderately resistant,susceptible and highly susceptible to C.zeina respectively,however,4,33,78,137 and 48 maize germplasms were highly resistant,resistant,moderately resistant,susceptible and highly susceptible to C.zeae-maydis.Only 77 germplasms had the same resistance to C.zeina and C.zeae-maydis,but 149 germplasms display the opposite resistance.It indicated that there were great differences in pathogenicity of C.zeina and C.zeae-maydis.The 76.99%germplasms were highly resistant,resistant or moderately resistant to C.zeina,but 61.67%germplasms were susceptible or highly susceptible to C.zeae-maydis.It indicated that the pathogenicity of C.zeina to most germplasms was weaker than C.zeae-maydis.5.The effects of C.zeina infection on host defense enzymes activity were studied clearly.The changes of defense enzymes activities in the resistant inbred line De813 and susceptible inbred line R151Ht1 A were studied after infection by C.zeina,in order to reveal physiological and biochemical mechanisms in host resistance to C.zeina.There were no obvious differences in the activities of defense enzymes PAL,POD,PPO,SOD and CAT in maize inbred lines with different resistance before infection by C.zeina.However,after infection by C.zeina,the activities of defense enzymes in resistant inbred line increased more quickly and could be maintained at a high level for a longer time,the peak activities of defense enzymes in resistant inbred line were higher than that of susceptible inbred line.The results showed that the physiological and biochemical responses of resistant inbred line were more rapid and lasting than that of susceptible inbred line after infection by C.zeina.6.A preliminary study on QTL mapping of resistance to C.zeina in maize was performed.A F2 segregating population was developed from a cross between resistant inbred line De813 and susceptible inbred line R151HtlA to C.zeina.Molecular markers linked to resistance to C.zeina were screened via simple sequence repeat-bulked segregant analysis(SSR-BSA).The F2 population(367 plants)was used to detect the degree of linkage between the molecular markers and resistance genes,in order to determine the chromosome locations of the resistance QTLs.The results showed there was a major QTL for resistance to C.zeina at bin 1.04-1.05 on the short arm of chromosome 1.It was located in an interval between the markers,its genetic map distance is 14.73cM and physical distance is about 4Mb.The genetic distances between the QTL and markers J91 and J96 were 8.03cM and 6.7cM,respectively.The QTL could explain 53.0498%of the phenotypic variation rate,the additive effect reached-2.7218,and the dominant effect reached 1.07.