How can mineral nutrition prevent plant disease? Mineral nutrition can affect two primary resistance mechanisms:• Physical resistance (e.g.cuticle layer, thickness of cell walls).• Chemical resistance e.g.nitrogen compounds (including alkaloids, cyanogenic glycosides and glucosinolates) terpenoids (rishitin, pisatin, gossypol) and phenolics.
• High nitrogen level in plant will produces the food for the pathogen• Excess nitrogen delays maturity of plant tissues and therefore increases the risk of disease infection and development• Excess nitrogen promotes thinner and weaker cell walls• The addition of nitrogen to the soil in different forms can also alter the activity of soil micro flora
• Increased nitrogen improves microclimate for pathogen• Facultative parasitic fungi like fussarium are actually suppressed by higher N levels• Unbalanced N :K ratio affects both yield and disease resistance.• High N applications can also effect the production of phenolic compounds needed for lignin• Increased Nitrogen level in the soil is congenial for , Ca, Si, K and Zn deficiency in the plants
Tentative Summary of the Effect of Nitrogen Levels on the Severity of Diseases Caused by Parasites Nitrogen LevelPathogen and Disease Low HighObligate parasitesPuccinia spp. (rusts) + +++Erysiphe graminis (powdery mildew) + +++Facultative parasitesAlternaria spp. (leaf spots) +++ +Fusarium oxysporum (wilts and rots) +++ +Xanthormonas spp. (spots and wilts) +++ +
• A. The cell wall is the combination of the two “mats of fibre” which are “glued” together by a “polymerized gel”• B. Middle lamella – The “polymerized gel” is like glue that binds the two layers together and forms the cell wall• C. Plasmodesmata – important in the translocation of nutrients and cellular material• D. Plasma membrane – The 2nd “line of defence” which keeps the disease “food” (simple amino acids & sugars) in the cell. This is also a very important part of natural disease resistance
Continued……2. Calcium is main component of the enzyme: Calcium polygalacturonates, which are required in the middle lamella for cell wall stability3. “Hypersensitive” response to disease (SAR or ISR)
• Phosphorus is important in early and strong root, stalk and stem development• Phosphorus is a vital component of Neuclic acid; the genetic "memory unit" of all living things• P as “Energy unit”• P as a “catalyst” in the biochemical reactions of plants• P produces more uniform and earlier crop maturity• It helps in withstanding the stress condition and there by increases the resistance
How K suppresses plant disease• Converts simpler molecule to complex and rigid molecules.• Potassium in proper quantity makes the plants to absorb Silica in the soil• Decreased cell permeability• Decreased susceptibility of tissue to maceration and penetration. because Potassium has role in the proper thickening of cell walls• Promotes the healing of wounds in plants, all of which increases the disease resistance
• Makes the plant to tolarate stress condition.• High K:Ca might leads to Ca deficiency and thus it decreases the resistance.• It helps to maintain cat ion concentration of cell.
Tentative Summary of the Effect of Potassium Levels on the Severity of Diseases Caused by Parasites. Potassium LevelPathogen and Disease Low HighObligate parasitesPuccinia spp. (rusts) ++++ +Erysiphe graminis (powdery mildew) ++++ +Facultative parasitesAlternaria spp. (leaf spots) ++++ +Fusarium oxysporum (wilts and rots) ++++ +Xanthormonas spp. (spots and wilts) ++++ +Based on Kiraly (1976) and Perrenoud (1977). 1998. “MineralNutrition of Higher Plants. 2nd ed. Horst Marschner.” p. 443.
Relationship Between Cat ion Content and Severity of Infection with Botrytis cinerea Pars. In Lettuce Cat ion content (mg/g dry wt.) Infection1 withK Ca Mg Botrytis14.4 10.6 3.2 423.8 5.4 4.1 734.2 2.2 4.7 1348.9 1.8 4.2 151 Infection index: 0-5 slight infection 6-10 moderate infection 11-15 severe infectionBased on Krauss (1971). 1998. “Mineral Nutrition of Higher Plants.” 2nd ed. HorstMarschner. P.447
THE EFFECT OF POTASSIUM ON ALTERNARIA LEAF SPOT, DEFOLIATION, and COTTON LINT YIELD
Potassium and soybean disease incidence on sandy soil