Week 3

• Learning Objectives

  • List chronologically and describe the major historical events in the development of the science of plant pathology
  • Explain the contribution of various people who helped greatly in the furtherance of the science of plant pathology
  • Discuss the “germ theory of disease” and its role in developing the science of plant pathology
  • Describe and discuss the progress of phytopathology in the Philippines from 1908 to the present
• Diseases of plants have caused devastations since time immemorial
• Fossil fungi about two billion years old have been found in pre-Cambrian charts
• Fossils of primitive gymnosperms contain fruiting bodies of fungi not unlike those that now parasitize old coniferous trees
• It is believed that plant diseases had been present on earth long before man appeared
• The Bible, Aristotle, Homer, and Theophrastus recorded diseases including blights, mildews, rusts, and blasts
• Superstitious beliefs regarding the nature and cause of plant diseases were rampant in the pre-scientific period
• Greeks and Hebrews attributed diseases to punishment for sins, bad weather, and unfavorable soil conditions
• Around 875 A.D., ergot epidemics caused by Claviceps purpurea swept through Europe
• Ergot of Rye is a disease caused by Claviceps purpurea, leading to severe health issues and death
• From the 17th century to the mid-19th century, early attempts at classifying plant diseases were made by Tournefort, Zallinger, Fabricius, and Unger
• Franz Unger is credited with the “autogenetic theory of disease”
• The concept of spontaneous generation prevailed due to microorganisms not being visible
• The compound microscope was invented in 1590, allowing the observation of microorganisms
• Hans and Zaccharias Jansen invented the compound microscope in 1590
• Hooke was the first to see plant cells in cork pith and illustrate a plant pathogenic microscopic fungus
• Leeuwenhoek in 1683 found bacteria, protozoa, and other microorganisms
• The “germ theory of disease” was enhanced by the works of various people including Pier Antonio Micheli, Tillet, Targioni-Tozzetti, Fontana, and Prevost
• Targioni-Tozzetti (1766) and Fontana (1767) did some studies on cereal rusts and concluded that the disease was caused by the rust fungi associated with it
• Prevost (1807) was the first to conclusively demonstrate that the bunt disease of wheat is caused by a fungous pathogen. He studied the formation of spores and their germination
• His work laid a firm foundation for plant pathology
• He also noted that wheat seeds soaked in a copper bucket resulted in smut-free plants and showed that copper sulfate prevented spore germination
• In 1858, Julius Kuhn wrote the first textbook on plant pathology entitled “The Diseases of Cultivated Plants, Their Causes, and their prevention”
• The period from 1850 to 1900 may be called the etiological period during which the theory that plant diseases were caused by pathogenic organisms was developed
• Louis Pasteur completed the overthrow of the theory of spontaneous generation in 1860 when he provided irrefutable evidence that microorganisms arise from pre-existing living entities
• Brefeld, Koch and Petri studied pure culture techniques for the growth of microorganisms
• The role of pollutants in causing plant diseases was demonstrated by German scientists as early as the 1880s
• Thomas J. Burrell (1878-1883) of the United States and J.H Wakker (1883-1889) of Holland showed that fireblight of apple and pear is caused by a bacterium
• E.F. Smith also studied several more bacterial plant diseases showing how important this pathogen are
• Bawden and Co-Workers in 1936 showed that crystalline virus preparation consistent of protein and nucleic acid. Kausche and co-workers in 1939 were the first to see the virus particles under an electron microscope
• Gierer and Scharamm established in 1956 that the nucleic acid is the infective component of the virus particle
• Nematodes as plant pathogens were first observed by Needham inside wheat galls (Kernels) in 1743. Berkeley noted root knot nematodes in galls formed in roots cucumber. Cobb conducted extensive studies on the morphology and taxonomy of plant parasitic nematodes from 1912 to 1932
• Flagellate protozoa were observed by Lafont in 1909 in the latex-bearing cells of laticiferous plants although these organisms parasitize the latex without causing apparent damage to the plant. Stahel in 1931 found protozoa causing abnormal phloem formation and wilting of coffee trees
• Mycoplasma-like organisms (MLOs) as plant pathogens were first reported by Doi and co-workers to infect aster yellows in Japan in 1967. Ishii and co-workers in 1965 observed that treating infected plants with tetracycline caused a temporary disappearance of the symptoms and the mycoplasma-like bodies. It also caused yellowing in some other crops. The MLOs are now called phytoplasmas
• Davis and co-workers observed that they called a spiroplasma in 1972. This motile, helical microorganism caused the stunt disease of corn. The phytoplasmas and spiroplasmas are placed taxonomically in class mollicutes, order mycoplasmatales. They are also referred to us the Mollicutes
• Diener in 1971 observed viroids as plant pathogens of potato causing spindle tuber disease. A viroid is an infectious ribonucleic acid molecule which is the smallest agent of plant disease and is not capable of independent multiplication. Cadang-cadang of coconut, citrus exocortis and potato spindle tuber are believed to be caused by viroid
• Burdeaux Mixture, a highly effective fungicide, was discovered by Pierre Marie Alexis Millardet in October 1882. This formed the foundation for the chemical control of plant diseases
• There has been increasing concern over the years regarding human and animal health, environmental pollution and pest/pathogen resistance that were brought forth as consequences of the continued use of fungicides, nematicides as pesticides in general
• The search for alternative methods of containing pests and diseases led to studies on biological control using antagonistic (to the pathogen) microorganisms, use of botanicals, and compounds that are generally
• Methods of containing pests and diseases

  • Use of fungicides
  • Use of nematicides
  • Biological control using antagonistic microorganisms
  • Use of botanicals
  • Compounds that are generally regarded as safe