Week 2

• Prepared by: 'FREDDIE D. CUAMBOT, PhD, Instructor'
• Learning Objectives

  1. Discuss the science and the art of plant pathology and describe how they are related

  2. Explain the various ways by which plant diseases affect man

  3. Discuss the various types of losses brought about by pathogens in plants and plant products
• Phytopathology or plant pathology

  Deals with the nature, causes and control of plant diseases. It is a science which looks into the characteristics of diseases, their causes, plant-pathogen interactions, factors affecting disease development in individual plants and in populations, and various means of controlling diseases
• The Science and Art of Plant Pathology

  • The art of plant pathology deals with the application of the knowledge gained from studying the science. This includes: Diagnosis of recognizing particular diseases by their symptoms and signs; Disease assessment and forecasting; Recommendation of appropriate control measures; Field application of suitable control measures
• The ultimate objective of plant pathology is to prevent or minimize plant diseases not only to increase food production but also to maintain the quantity and quality of harvested fresh commodity until it reaches the consumer
• Human beings (as well as other animals) exist on earth solely as guests of the plant kingdom because only the green plants can convert the energy from the sun into food
• We depend on plants not only for food but also for our clothing and shelter needs and for numerous luxuries. When diseases kill plants, all other forms of life on earth are adversely affected
• Economic Importance of Plant Diseases

  • History has recorded numerous cases of human suffering, death and upheavals due to plant disease epidemics. For example, the potato late blight disease caused famine and death of more than a million people in Ireland in 1845-46
• Famine and malnutrition occur in many parts of the world, especially in underdeveloped parts of Africa, Latin America, and Asia when plant disease control measures are inadequate or unknown
• The increasing world population compounds the problem as this means more mouths to feed and less agricultural land to till
• In the Philippines alone, enormous losses have been brought about by plant diseases. For example, the cadang-cadang disease of coconut has cost the country over a hundred million dollars since it was observed in 1918
• Downy mildew, the nemesis of corn, used to destroy as much as 95% of the corn crop before its control by chemical seed treatment was discovered in 1978. The loss amounted to over 170 million pesos annually
• The Tungro disease of rice affected 70,000 hectares of rice fields in 1971 alone, causing a loss of 1.22 million cavans of rough rice valued at P30,357,000
• Coffee and Citrus plantations used to be profitable sources of income in Batangas province until the former was ravaged by coffee rust and the latter by citrus decline
• Effects of diseases on plants

  1. Reduction in yield of diseased plants

  2. Decrease in photosynthetic capacity due to leaf spot and leaf blight

  3. Diminished host vigor by root pathogens

  4. Lessening of fruits fit for harvesting and marketing by fruit-rotting and fruit-spotting microorganisms
• Deterioration of harvested produce during storage, marketing, and transport accounts for tremendous losses in our food supply. The amount of food lost daily is enough to feed the world populations
• Losses may also occur as a reduction in the quality of the produce. Citrus fruits with numerous canker or scab lesions are rather unsightly and usually command lower prizes in the market
• Moldy cereals, pulses, oilseeds, and other commodities suffer nutrient losses, are discolored, and may carry-off flavors that are unacceptable to consumers
• Diseases of forest trees may reduce the strength of the wood pulp and cause undesirable discoloration
• Infected seeds germinate poorly, if at all. Those that germinate often produce diseased seedlings
• Many microorganisms that colonize plant products produce poisonous substances or toxins that endanger the health of the consumer
• A pathogen often causes the host plant to become weak and susceptible to attack by other pathogens

  For example, nematodes injure the roots of plants, and the injured areas serve as an avenue for the entrance of pathogenic microorganisms
• Diseases increase the cost of production and handling. One major input of production is the cost of controlling diseases
• In many instances, the application of control measures results in higher economic losses. The high cost of control is passed on to the consumer, thus, consumers pay a staggering price for the produce
• Herbert H. Whetzel: '“For what will it profit us if all the ill and diseases of the human race be banished and we then face starvation because of the diseases and pests of our food plants?”'