D. Use of balanced nutrition
Host nutrition plays an important role in host defense. Different macro-nutrients (NPK) and micro-nutrients (eg. Ca, Mn, Fe, Si etc) increase/decrease the resistance of different plants to plant pathogens or increase/decrease the pathogenicity of plant pathogens and therefore, influence the amount of disease produced.
Role of macro-nutrients (NPK):
N: Plants excessively supplies with N have soft, succulent vegetative tissue with little resistance to penetration by fungal hyphae or sucking and chewing insects which might be the vectors of many pathogens. The excessive growth due to overdose of N also creates micro-climatic conditions (such as more humidity) favorable for fungal and bacterial diseases. For example, over-supply of N (and inadequate K) can result in cereal lodging; humidity remains longer in lodged crops giving ideal conditions for germinating of fungal spores and multiplication of bacteria. Plants fertilized with high levels of nitrogen (which produces abundant succulent tissue) are also more susceptible to bacterial soft rot.
P: Fertilization of calla lilies with super-phosphate increased their susceptibility to bacterial soft rot. This fertilizer was found to increase the expression of plant cell wall degrading enzymes of the bacteria.
K: It was found that the use of potassium (K) decreased the incidence of about 70% fungal and bacterial diseases, and 40% of viral diseases (Perrenoud, 1990). K deficiency can result in cracks and lesions on the surface of leaves and fruits providing easy access to fungi and bacteria.
Role of micro-nutrients (Ca++, Mn, Fe, Si):
Ca++: On the other hand, if calcium is added to soil or is fed to plants in liquid fertilizer, it reduces soft rot diseases. Divalent Ca++ acts as a cross linker for pectate in plant cell walls to make the walls stronger and thus more resistant to pathogen attack. Calcium has also been reported to down-regulate (inhibit) the de-gradative enzymes genes of soft rot bacteria and fungi. These enzymes dissolve the middle lamella (inter-cellular cement) of plant cell walls. With insufficient Ca, cell walls leak low molecular weight organic compounds used as food by pathogens (living in inter-cellular spaces).
Mn: Manganese and copper are involved in activating the lignin-synthesizing metabolic pathways. Lignification (lignin is in-soluble in water) of cell walls is needed to provide resistance against many pathogens. The synthesis of soluble phenols (anti-pathogen toxic substances) is also stimulated by Mn. Manganese also inhibits the activities of some important pathogen enzymes. Acute deficiency of Mn can also decrease or inhabit photosynthesis which weakens the plant host.
Fe: Iron also plays a role in plant defenses. Mutant Arabidobsis plants unable to produce the iron storage protein ferritin were found to be more susceptible to soft rot bacterial disease (Erwinia chrysanthemi) than wild type plants (which can produce feritin).
Silicon (Si): Silicon increases the resistance of plants against some pathogens (eg., rice blast fungus, Pyricularia oryzae) by forming some kind of physical barrier to penetrating fungal hyphae.
SUMMARY OF THE LECTURE:
Nutrition also plays a big role in protecting plants against different pathogens. In general, if plants are well-nourished, they will be more resistant to the attack of plant pathogens. Different nutrients/elements play different roles in host resistance. A brief summary is given below:
N: Balanced N is helpful. However, excessive use of N causes lodging, soft tissue production etc., which makes plants more susceptible to diseases.
P: Balanced P is important but excessive P causes disease problems.
K: K deficiency causes cracks on surface of plant tissue, providing easy entry to pathogens.
Ca++: It cross links various components of plant cell walls making walls stronger and more resistant to pathogens.
Mn and Cu: They help in the synthesis of lignin, making cell walls very strong and resistant to pathogens.
Fe: It is needed for host resistance. Plants with ferritin (Fe-protein) are more resistant to pathogens.
Si: It provides physical barrier, making the entry of pathogens into plant tissues more difficult.
- Teacher: Dr. Musharaf Ahmad
Agron-602 Principles of Agronomy 4(2-4)
Agronomy, definition and scope.
Tillage-its objectives and types.
Quality seed and its uses.
-Crop nutrients, manures and fertilizers, classification, composition, sources and methods of application, green manuring.
Irrigation management, irrigation methods, water-use efficiency.
Weeds, insect pests and diseases of major field crops.
Crop rotation principles and types.
Harvesting storage and marketing of farm produce.
Integration of factors of crop production for effective use of various agricultural inputs.
Demonstration and use of tillage implements, preparatory tillage,
seedbed preparation and intercultural operations,
Seed identification and purity analysis.
Identification of organic and inorganic fertilizers and manures.
Calculation of nutrient cum-fertilizer unit value.
Visits to university farms and grain stores.
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2. Arnon, I. 1992. Agriculture in Dry Lands Principles and Practices. Elsevier, London.
3. Balasubramaniyan. 2004. Principles & Practices of Agronomy Pak Book Corp. Lahore.
4. Brady, N.C. and R.R. Weil. 2001. The Nature and Properties of Soils. Prentice Hall, New Delhi
5. De, G.C. 1995. Fundamentals of Agronomy. Oxford and IBH Pub. Co., New Delhi.
6. Havlin, J., S. Tisdale, W.L. Nelson and J.D. Beaton. 2004. Soil Fertility and Fertilizers: An Introduction to Nutrient Management. 7th Ed. Prentice Hall, New Delhi
7. Khan S.R.A. 2001. Crop Management in Pakistan with Focus on Soil and Water. Directorate of Agricultural information, Punjab, Lahore.
8. Khalil, I.A & A. Jan. 2002 Cropping Technology. National Book Foundation, Islamabad. 14
9. Michael, A.M. 1990. Irrigation: Theory and Practice. Vikas Pub. House, New Delhi.
10. Nazir, M.S. 1994. Crop Production. National Book Foundation, Islamabad.11. Pratley, J.E. 2003. Principal of Field Crop Production. Oxford University Press, Oxford
- Teacher: Dr. Asim Muhammad