Dissertation > Excellent graduate degree dissertation topics show

Etiology Studies on Broccoli Brown Stem Disease and Its Control Strategies

Author: WangHanRong
Tutor: SongFengMing
School: Zhejiang University
Course: Plant Pathology
Keywords: brown stem disease of broccoli identification Hyaloperonospora parasitica disease development control strategy
CLC: S436.35
Type: Master's thesis
Year: 2010
Downloads: 47
Quote: 0
Read: Download Dissertation

Abstract


Broccoli is a very popular vegetable among customers worldwide. Since it was introduced in 1980’s, Zhejiang Province has now become the largest broccoli production base in China, which has 10000 ha broccoli production per year, accounting for 70% of the total in China, and provides annually more than 300 000 ton products.However, diseases have become main problems in broccoli production in Zhejiang Province. Among them, brown stem disease, also called blackheart disease, is one of the most serious diseases that cause significant loss in broccoli production in Taizhou, Ningbo, Shaoxing and Hangzhou since 1999. Brown stem disease often causes significant symptom on stems and in diseased plants, vascular and stem epidermis turn brown and hollow. Typically, seriously diseased plants completely loss commercial value. It was estimated that the indicidence of the brown stem disease in broccoli ranges from 25% to 80%, leading to significant yield losses during recent years. Therefore, the brown stem disease has become the bigget bottleneck that threatens the sustainable development of the broccoli production in Zhejiang Province.In recent years, I performed field survey to estimate incidence of the broccoli brown stem disease, studied factors that affect disease development, and developed some useful control strategies. Results from these studies are summarized as follows. (1) Etiological identification of the causal agent of the broccoli brown stem diseaseTo identify the possible causal agent of the broccoli brown stem disease, I carried out a series of experiments including tissue culture, microscopic examination and observed a lot of hyphae and haustoria in diseased broccoli plants, which are similar to Hyaloperonospora parasitica causing downy mildew diseases in plants. The pathogen is unculturable on synthetic medium but can grown on broccoli tissues in vitro and in vivo. Cultures grown from broccoli tissues can cause significant symptom on broccoli that is similar to the symptom observed in diseased plants in the field. Meanwhile, rDNA-ITS (internal transcribed spacers) of pathogens was amplified and homology searches against NCBI datatbase revealed that the obtained sequences showed 99% similarity at nucleotide sequence level to those in Hyaloperonospora parasitica. Taken together, the casual agent of the broccoli brown stem disease was identified as H. parasitica Constant (Pers.ex Fr.). (2) Factors afftecting broccoli brown stem disease in fieldI further carried out field survey and a series of experiments to investigate the factors that affect developmentof broccoli brown stem disease in field. Results from these studies indicate that temperature and relative humidity (RH) are critical factors that afftect broccoli brown stem disease. Temperature is a prerequisite for brown stem disease, and decides the timing of disease appearance and speed of spread.Continuous raining with the temperature of above 10℃favors pathogen invading and disease development. However, low temperature (bellow 10℃) suppresses disease development. Relative humidity is also a determinant that affects disease severity. Waterdrops on the plants is the most important factor of spore germination and infection. Generally, continuous raining and fog days (more than 5 d) increase disease severity.Broccoli cultivars are another factor that affects development of brown stem diseases. We studied 15 broccoli cultivars for their resistance levels to brown stem disease and found that "youxiu" and "lvxiong 90" are the most disease resistant cultivars. (3) Spatial distribution pattern and sampling technique for broccoli brown stem diseaseWe studied the spatial distribution pattern and sampling technique for the broccoli brown stem disease. The tests of frequency distributions indicated that the all samples did not fit to the evenness distribution model, but to the neyman distribution model. The analyses of aggregation indexes showed that Lloyd’s index of mean crowding (m*) ranged between 2.493 and 3.207 and other indexes were as follows:cole’s index (I) of dispersion>0, David and moore’s index (m*/m)>1, Kuno index (Ca)>0, dispersion index (C)>1, and negative binomial index (K)>0. All these data suggest that the tested samples fit to the aggregate or contagious distribution patterns. The distribution pattern of the infected plants shad the tendency of gathering with the density of broccoli increased. The sampling numbers decreased with increase of the pathogen index. The sampling numbers were 77 plants when the incidence was 15. The sequence sampling procedure was based on the equation To (n)=1.35N±1.1573(?)N. (4) Effect of microelements on broccoli brown stem diseaseTo find the possible involvement of microelements in broccoli brown stem disease, I analyzed the potentials of four different microelement fertilizers such as cuikangbaoli, liangfengsupeng, liangfengsumei and liangfengsugai in control of the disease. Results showed none of the fertilizers tested could suppress the disease. This alsoh indicates that the broccoli brown stem disease is not physiological disease caused by nutrient deficiency. (5) Control strategies of broccoli brown stem diseaseI further studied the possible control strategies for management of broccoli brown stem disease. During my study, I screened and identified two disease resistant cultivars, "youxiu" and "lvxiong 90", and introduced these two cultivars to broccoli production in large scales. Fungicides were also screened and tested for their efficiency in control of broccloli brown stem disease and found that amixida (azoxystrobin) was the best chemical, giving a control efficiency of 89.74%. If mixed with spray of 300X oil "lvying", the control efficiency of amixida can be further improved. My studies also suggest that the control action must be taken when continuous raining (fog) and suitable temperature (10-27℃) last more than 5 d at bud or prophase period.Efficient and safe control strategies have been concluded based on the concept of integrated pest management, including rational crop rotation, cleaning of diseased residues, application of resistant varieties, plus B and low N fertilization, physical and biological control by turn, timely application of chemicals. These strategies have been widely applied in about 92% of broccoli fields in Zhejiang province and desired efficiency of disease control was achieved in the last several years.

Related Dissertations

  1. Research on the Attitude Controller Design and Control Strategy of High Altitude Platform,V249.1
  2. Temperature Drift Modeling and Compensation of Fiber-Optic Gyroscopes,V241.5
  3. Simulation and Analysis about Switched Reluctance Generator Power Supply System,TM31
  4. Research on Vector Control System of Induction Motor Based on DSP,TM346
  5. Compensation Methods of Different Speech Coding for Speaker Recognition,TN912.34
  6. Design and Simulation of UHF RFID System Based on the Protocol of EPC C1G2,TP391.44
  7. The Software Component Modeling Method Based on Feature and Its Application in VMI Management System,TP311.52
  8. Research on the Control and Remedy of Nanopositioning Stage Drived by Piezo Material Lead Zirconate Titanate,TP273
  9. The Study on Rhinoceros Horn and Its Imitation,TS932.2
  10. Study on Antioxidant Components of Tibetan Medicine Sanguo Tang San,R29
  11. Over-voltage Identification of Transmission Line Based on Hilbert-Huang Transformation,TM866
  12. Study of Synchronous Generator Excitation Control Based on Neural Network Identification,TM31
  13. Identification on the Species and Pathotypes of Four Cereal Cyst Nematode Populations from Western and Northern Henan,southern Hebei and Evaluation of Wheat Cultivars Resistance to Two Populations,S435.121
  14. Isolation and Identification of Avian Pathogenic Escherichia Coli from Chicken and Characterizations of Its Virulence-Associated Genes,S852.61
  15. Isolation and Identification of Infectious Bronchitis Virus and Sequence Analysis of Its S1 Gene and N Gene,S852.65
  16. Isolationand Identification of Porcine Parvovirus and Parts of Its Biological Characteristics,S852.65
  17. Research on Identification System of Cashmere and Wool Fiber,TS101.921
  18. Study of Isolation and Identification on Antimicrobial Substances Produced by Lactobacillus Acidophilus NX2-6,TS201.3
  19. A Study of the Isolation and Identification of Fusarium Wilt Germ in Sesame and the Characteristics of Sesame Germplasm Anti-Fusarium Wilt Disease,S435.653
  20. Genetic Diversity of Magnaporthe Grisea from Rice in Jiangsu and Identification of Resistance Rice Blast Gene,S435.111.41
  21. Isolation and Identification of a Probiotic Strain Capable of Producing Glycerol and Optimization of Fermentation Conditions for the Strain,S823.5

CLC: > Agricultural Sciences > Plant Protection > Pest and Disease Control > Horticultural Crops Pest and Disease Control > Vegetable pests > Cabbage pests and diseases
© 2012 www.DissertationTopic.Net  Mobile