A New Disease Of Tomato Wilt Caused By Plectosphaerella Cucumerina In China

Tomato (Solanum lycopersicum Mill.) is one of the most important vegetable crops in China. A newly occurred tomato disease, Tomato Wilt caused by Plectosphaerella cucumerina, has becomed more and more serious in recent years. It caused varying degrees of yield losses in tomato production, the disease incidence rate up to 100% and even no harvest in serious disease plastic greenhouse. Because limited knowledgement was known about the pathogenetic characters and control measures, the Tomato Plectosphaerella Wilt was increased prevalence and it was an urgent problem that has to be solved. In order to solve these problems, the aspects of disease symptoms, etiology, pathogenicity, geographical distribution and varieties resistance were studied systematicly. Besides, a molecular technique for early diagnosis was established. It was provided a theoretical basis for disease early warning and monitoring and disease prevention and control. The main findings were as follows:1. First reported a new disease of Tomato Plectosphaerella Wilt in China, and the causal agent was Plectosphaerella cucumerinaIn this sudy, a new disease of Tomato Plectosphaerella Wilt in huludao city of Liaoning Province was found and identified for the first time. By Koch’s postulates testing and morphological identification in combination with rDNA-ITS sequences analysis and molecuar method validation, the pathogen was identified as P. cucumerina which belongs to Fungi, Ascomycota, Pezizomycotina, Sordariomycetes, Hypocreomycetidae, plectosphaerellaceae, Plectosphaerella. Also, symptoms of the disease by field investigation and artificial inoculation test were studied. At beginning of fruit set, symptoms were chlorosis of lower leaves and lack of turgidity in young leaves. Severely affected plants were wilted and stunted as fruit was becoming matural. Primary and secondary roots became necrotic with few fine feeder roots. The symptoms of the disease were very similar to some physiological diseases and Tomato Fusarium Wilt.2. Systematic study of Biological Characteristics, host range and primary infection source of P. cucumerinaBiological characteristics results showed that the mycelia of the pathogen could grow better on PDA, PSA and MEA. The pathogen could effectively use many kinds of carbonhydrates and nitrogen sources. Sucrose, glucose and mannitol were better carbonhydrates, and peptone and yeast extract were the better nitrogen sources. The mycelia could grow under 5℃ to 35℃, and growed best at 27℃. The optimum temperature for conidial germination was 24℃. Mycelial lethal temperature was 50℃, 10min. And the optimum pH value was 6-8. The pathogen could infect eggplant, pepper, tomato, lettuce, bitter lettuce, melons, cucumbers, cabbage and oilrape under artificially inoculation.The pathogen survival condition detection results showed that P. cucumerina in soil and diseased plant debris could overwinter successfully and become primary infection sources of the disease. And the pathogen could not transmitted by seeds. Soil moisture was closely related to the survival time of the pathogen. The number of viable pathogen propagules decreased progressively with time. Pathogen could survive for 22 months and 18 months, respectively at 0% and 25% soil moisture, and it survived longer at 50%,75%,100%,150% soil moisture and water. Better conservation was obtained in water where pathogen remnants of approximately 102CFU/mL after 2 years. According to the biological research results and field investigation, disease cycle of the pathogen was constructed.3. Determined the geographical distribution of P. cucumerina on tomatoUsing molecular and plant pathology methods,847 tomato roots samples from 29 cities covering 10 provinces were isolated and identified. The results showed that the pathogen were isolated from samples of Liaoning, Hei Longjiang, Jilin, Hebei, Shandong, Shanxi and Hebei province. The isolation frequency of samples was different. Isolation frequency of Liaoning province was 10-82.78% and Hei Longjiang, Jilin, Shandong and Shanxi was 4.8-32%.4. Establishment of the Nested PCR Detection System of P. cucumerinaBased on the rDNA-ITS sequence of P. cucumerina and other common pathogens in soil, specific outer primers PcF1/PcR1 and intermal primers PcNF1/PcNR1 were designed. Combined these two kinds of primers, a nested PCR protocol was established. We could obtain a 195bp sequence from P. cucumerina, but nothing from other pathogens in the test. The sensitivity of this assay was lfg/μL DNA of P. cucumerina. The nested PCR detection results showed that pathogen could be detected on tomato roots and leaves at the second day after inoculation. Field test showed that the detection rate was 56% by nested PCR of 100 samples randomly collected in the field. And disease incidence of the tomato in sample collection field was 49%. These data showed that the nested PCR could be effective to diagnose disease in in early stage of tomato production. It was provided theoretical and technique basises for disease early warning and monitoring, industrial seedling, and disease control.5. Rule for evaluation of resistance to Tomato Plectosphaerella Wilt was developed and the resistant varieties were screeded by the rule.After 3 years tests, a series of techniques including inoculum preparation, resistance identification, disease investigation, resistance evaluation were developed. The technology system for evaluation of resistance to Tomato Plectosphaerella Wilt was established. Using the technique,46 tomato varieties which used widely in North China, were evaluated for resistance to Tomato Plectosphaerella Wilt. The result showed that there were 6 varieties of highly resistant(HR) resources and accounted for 13.0%of the total. Resistant(R) resources were 10 varieties and moderately resistant(MR) resources were 12 varieties, which accounted for 21.7% and 26.1% respectively. And the frequency was 21.7% and 26.1%, respectively. Susceptible(S) resources were 11 varieties, accounted for 23.9% of the total. And highly susceptible(HS) resources were 7 varieties, accounted for 15.2% of the total.