Factors Responsible for Non Parasitic Disease
1. Unfavourable Temperature:
a. High Temperature Effects:
1. Plants are generally injured faster and to a greater extent when temperature becomes higher than maximum for growth.
2. High temperature are usually responsible for sun solid injuries appearing the sun exposed sides of fleshy fruits and vegetables.
Ex. Sun scald of apple, peppers, tomato, onion- bulbs, potato tubers, canker of linseeds.
b. Low Temperature Effects:
1. Low temperature causes greater damage to crops than high temperature.
2. Blotch type necrosis in Potato is due to freezing injury.
3. The frost injuries involved killing of buds of peach, cherry, killing of flowers, young fruits and sometimes succulent twings of most trees.
4. Low winter temperature may kill young roots of trees such as apple and may also cause bark splitting and canker development.
2. Unfavourable Light:
Lack of sufficient light or absence of light retards chlorophyll formation and promotes slender growths with long internodes, thus leading to pale green leaves, spridly growth and premature drop of leaves and flower. This condition is known as “Etiloation”.
3. Moisture Effects:
A. Low Moisture Effects:
Plant suffering from lack of sufficient soil moisture usually remain stunted are pale green to light yellow, have few small dropping leaves and finally in absence of moisture plant dry and wilt.
B. High Moisture Effects:
Stagnation of water or excessive moisture by flooding in the field may cause decay or rotting of fibrous root of plants resulting into wilting. Primarily due to accumulation of toxic materials around the root and base of stem and also due to non availability of nutrients.
Ex. Tip burn of paddy.
Another common symptom of house plants caused by excessive moisture is swelling. Edema appears as small bumps on the lower of leaves or on stem.
4. Inadequate Oxygen:
When there is excessive respiration in closed atmosphere the entire oxygen supply may be exhausted resulting in disintegration of cells due to enzymic action.
Ex. Black heart of potato.
5. Atmospheric Impurities or Air Pollution:
Presence of injuries gases in the atmosphere may cause definite injury to plant and plant parts.
More serious and wide spread damage is caused to plant in the fields by chemicals such as Ozone, sulphur dioxide hydrogen fluoride, nitrogen dioxide, peroxyaacotyl nitrates.
Ex. Black tip of mango necrosis. Fruit on trees is close proximity to brick kilns may bear necrotic lesions and become useless for sale and consumption. The smoke of kills polluted the air with toxic gases like gases like sulphur dioxide which caused necrosis of tissues.
6. Toxic effects of Decomposition Organic Matter in Soil and Soil Mineral Toxicity:
Crop residue decomposing in soil produce toxic substances such as fatty acids which produce symptoms of damping off, root rot, wilt and nutritional deficiency.
Excessive amount of sodium salt especially sodium chloride, sodium sulphate and sodium carbonate raise the PH of the soil and cause alkali injury i.e Chlorosis, stunting, boron, manganese and copper have been most frequently implicated in mineral toxicity disease. Excess boron is toxic to many vegetable and trees, Excess manganese is known to cause crinkle leaf disease in cotton.
7. Herbicidal Injury:
Some of the most frequent plant disorder seems to be the result of extensive use of herbicides. Increasing number of herbicides in use for general or specific weed control has created problems.
8. Nutritional Deficiencies or Disorder in Plants:
i) Deficiency of minerals viz Nitrogen, Phosphorus, potash, manganese , magnesium, boron, zinc, copper , iron, etc. results in disorders in plant metabolism and cause hunger signs in the crops.
ii) Excess of minerals disturbs nutritional balance needed for good metabolism in the palnt, thus hindering the effect of essential element.
iii) The deficiencies and excess of minerals also reduce the resistance of plant to fungal, bacterial and other diseases.
iv) The kind of symptoms produced by deficiency of a certain nutrient depend primarily on the functions of that particular element in the plant.
9. Plant Disease Due to Lack of Minerals
Other Improper Agricultural Practises:
A variety of other agricultural practices improperly carried out, many cause consideration damage to plants. Improper application of chemical viz. fungicides insecticides, nematicides and fertilizers at too high concentration results, into losses. Spray injury results into leaf burn or spolting or rosseting of fruits. Excessive or deep cultivation between rows of growing plants may pull roots of many plants.