Author: Pravin L. Deshmukh
Nutritional disorders are basically physiological disorders in the plants that affect productivity as well as the quality of fruits. Disturbance in the plant metabolic activities resulting from an excess or deficit of environmental variables like temperature, light, aeration and nutritional imbalances result in disorders. In fruit crops, the deficiency of micronutrients causes many more disorders than that of macronutrients. Nutritional disorders have become widespread with diminishing use of organic manures, adoption of high density planting, use of root stocks for dwarfing, disease and salt tolerance, unbalanced NPK fertiliser application and extension of horticulture to marginal lands. To get high quality fruit and yields, micronutrient deficiencies have to be detected before visual symptoms are expressed.
The deficiencies of Zn, Mn and B are common in sweet orange, acid lime, banana, guava and papaya in India. To correct both visual and hidden micronutrient deficiencies, appropriate foliar and soil applications are necessary. The description of physiological and nutritional disorders in crops includes a number of technical terms and it is essential to understand the terms for better identification of symptoms. Some common terms are, bronzing (development of bronze or copper colour on the tissue), chlorosis (loss of chlorophyll resulting in loss of green colour leading to pale yellow tissues), decline (onset of general weakness as indicated by loss of vigour, poor growth and low productivity), die-back (collapse of the growing tip affecting the younger leaves), firing (burning of tissue accompanied with dark brown or reddish brown colour), lesion (a localised wound of the leaf/stem tissue accompanied with loss of normal colour), necrosis (death of tissue), scorching (burning of the tissue accompanied with light brown colour resulting from faulty spray, salt injury etc.)
Some crops are more sensitive than others to the deficiency of a micronutrient and it can be inferred that the critical concentration of a nutrient is not same for all the crops. The susceptibility or tolerance rating of crops to nutrient deficiencies shows considerable variation due to wider hereditary variability within a crop species. Further, terms such as low, moderate or high are very relative and should be used with caution.
Diagnostic plant symptoms of nutrient element insufficiencies
When a nutrient element insufficiency (deficiency and/or toxicity) occurs, visual symptoms may or may not appear, although normal plant development will be slowed. When visual symptoms do occur, such symptoms can frequently be used to identify the source of the insufficiency.
Deficiency symptoms: Visual symptoms of deficiency may take various forms, such as….
- Stunted or reduced growth of the entire plant with the plant itself either remaining green or lacking an over-all green colour with either the older or younger leaves being light green to yellow in colour.
- Chlorosis of leaves, either interveinal or of the whole leaf itself, with symptoms either on the younger and/or older leaves, or both (chlorosis is due to the loss or lack of chlorophyll production).
- Necrosis or death of a portion (margins or interveinal areas) of a leaf, or the whole leaf, usually occurring on the older leaves.
- Slow or stunted growth of terminals (rosetting), the lack of terminal growth, or death of the terminal portions of the plant.
- Reddish purpling of leaves, frequently more intense on the underside of older leaves due to the accumulation of anthocyanin.
Visual symptoms of toxicity may not always be the direct effect of the element in excess on the plant, but the effect of the excess element on one or more other elements. For example, an excessive level of potassium (K) in the plant can result in either a magnesium (Mg) and/or calcium (Ca) deficiency, excess phosphorus (P) can result in a zinc (Zn) deficiency, and excess Zn in an iron (Fe) deficiency. These effects would compare to elements, such as boron (B), chlorine (Cl), copper (Cu), and manganese (Mn), which create visual symptoms that are the direct effect of an excess of that element present in the plant. Some elements, such as aluminium (Al) and copper (Cu) can affect plant growth and development due to their toxic effect on root development and function.
In some instances, a nutrient element insufficiency may be such that no symptoms of stress will visually appear with the plant seeming to be developing normally. This condition has been named hidden hunger, a condition that can be identified by means of either a plant analysis and/or tissue test. A hidden hunger occurrence frequently affects the final yield and the quality of the product produced. For fruit crops, abnormalities, such as blossomed rot and internal abnormalities may occur, and the post harvest characteristics of fruits and flowers will result in poor quality and reduced longevity.
Climatic and other causes
The occurrence of the symptoms may not necessarily be the direct effect of a nutrient element insufficiency. For example, stunted and slowed plant growth and the purpling of leaves can be the result of climatic stress, cool air and / or root temperatures, lack of adequate moisture, etc. Damage due to wind, insects, disease and applied foliar chemicals can produce visual symptoms typical of a nutrient element insufficiency. In all these cases, carefully followed diagnostic techniques must be employed –particularly the use of plant analyses and / or tissue tests if the cause for visual disorders is to be correctly identified.
Element/status Visual symptoms
Deficiency: Light green leaf and plant colour with the older leaves turning yellow, leaves that will eventually turn brown and die. Plant growth is slow, plants will be stunted, and will mature early.
Toxicity: Plants fertilized with ammonium-nitrogen (NH4-N) may exhibit ammonium toxicity symptoms, with carbohydrate depletion and reduced plant growth. Lesions may occur on plant stems, there may be a downward cupping of the leaves, and a decay of the plants under moisture stress. Blossom-end rot of fruit and Mg deficiency symptoms may also occur.
Deficiency: Plant growth will be slow and stunted, and the older leaves will have a purple coloration, particularly on the underside. High P may also interfere with the normal Ca nutrition, with typical Ca deficiency symptoms occurring.
Deficiency: On the older leaves, the edges will look burned, a symptom known as scorch. Plants will easily lodge and be sensitive to disease infestation. Fruit and seed production will be impaired and of poor quality.
Deficiency: The growing tips of roots and leaves will turn brown and die. The edges of the leaves will look ragged as the edges of emerging leaves stick together. Fruit quality will be affected with the occurrence of blossom-end rot on fruits.
Deficiency: Older leaves will be yellow in colour with interveinal chlorosis (yellowing between the veins) symptoms. Plant growth will be slow and some plants may be easily infested by disease.
Deficiency: A general overall light green colour of the entire plant with the older leaves being light green to yellow in colour as the deficiency intensifies.
Deficiency: Abnormal development of the growing points (meristematic tissue) with the apical growing points eventually becoming stunted and dying. Flowers and fruits will abort. For some grain and fruit crops, yield and quality is significantly reduced.
Deficiency: Younger leaves will be chlorotic and plants will easily wilt. For wheat, a plant disease will infest the plant when Cl is deficient. Premature yellowing of the lower leaves with burning of the leaf margins and tips. Leaf abscission will occur and plants will easily wilt.
Deficiency: Plant growth will be slow and plants stunted with distortion of the young leaves and death of the growing point.
Deficiency: Interveinal chlorosis will occur on the emerging and young leaves with eventual bleaching of the new growth. When severe, the entire plant may be light green in colour.
Deficiency: Interveinal chlorosis of young leaves while the leaves and plants remain generally green in colour. When severe, the plants will be stunted.
Deficiency: Symptoms will frequently appear similar to N deficiency. Older and middle leaves become chlorotic first, and in some instances, leaf margins are rolled and growth and flower formation are restricted.
Deficiency: Upper leaves will show interveinal chlorosis with an eventual whiting of the affected leaves. Leaves may be small and distorted with a rosette form.
About Author / Additional Info:
Ph.D. Scholar, Department of Horticulture, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola, Maharashtra-444104.