Rice is a most important cereal crop that grown from corner to corner the world and its meets the food demand of more than half of the world population. There is a extensive number of variations in rice yield from one region to other more so in Pakistan. For improving and sustaining the rice yield to meet the demand of fast increasing population, there is a need to apply all the ingenuity of rice science. Managing the nutrient deficiencies, toxicities and pathogenic diseases is key to achieve this objective. A simple and easy to use visual diagnostic tool is very effective for timely identifying the symptoms and applying the corrective measures at field level.
Normally 16 elements are considered as essential, out of which N, P and K are the primary macronutrients; Ca, Mg and S are the secondary macronutrients; and Fe, Mn, Zn, Cu, B, Mo and Cl are the micronutrients. For optimum growth and reproduction all the essential nutrients are required by plants in balanced proportion. Nutrient deficiency occurs when an essential nutrient is not available in sufficient quantity to meet the requirements of a growing plant while the toxicity occurs when a nutrient is in excess of critical limits of plant. Both the situation hamper the normal plant growth and exhibit characteristics symptoms.
Plant diseases also show visible symptoms like nutrient deficiency and toxicity symptoms, sometimes it is difficult to distinguish one from an- other and requires expertise on the visual diagnosis. Though laboratory based molecular techniques are accurate tools, the visible symptoms based on the morphological characters sometimes are the only means of diagnosis available to farmers for adopting the corrective measures against the pathogenic diseases.
In most of the cases, interpreting visual nutrient deficiency, toxicity and disease symptoms in plants can be difficult, even for the most experienced eyes and hence plant analysis or soil testing is necessary to confirm the result. Many symptoms appear similar and multiple deficiencies and/ or toxicities can occur at the same time, making it even more confusing. Nutrient deficiencies can also be confused with symptoms of disease, drought, excess water, herbicide and pesticide damage and pest attack.
This article is about visual symptoms of nutrient deficiency, toxicity and some major disease in rice crop is designed as a management guide to identify, understand and manage the occurrence of nutrient deficiencies, toxicities and diseases in rice crop. We hope that this book will act as an useful tool for rice researchers, extension workers, students and farmers, and would help to boost up the rice production and productivity.
| Elements | Functions |
| Nitrogen (N) | It is integral part of chlorophyll. It promotes rapid growth, increase plant height and tiller number. It plays an important role in synthesis of proteins, enzymes, hormones, vitamins, alkaloids, nucleic acids (DNA, RNA) etc. |
| Phosphorus (P) | It plays central role in energy transfer and protein metabolism. It is a constituent of sugar phosphates, nucleotides, nucleic acids, co-enzymes and phospholipids. |
| Potassium (K) | It helps in osmotic and ionic regulation and is required as a co-factor or activator for 40 or more enzymes. It imparts disease and drought resistance. |
| Calcium (Ca) | It is involved in cell division and plays a major role in the maintenance of membrane integrity. It is a constituent of cell wall as calcium pectate. |
| Magnesium (Mg) | It is central part of chlorophyll and it is required in several enzymes involved in phosphate transfer. It is structural component of ribosomes. |
| Sulfur (S) | Somewhat like phosphorus, it is involved in plant cell energetics. It plays an important role in plant lipid synthesis and amino acids. |
| Zinc (Zn) | It is an essential component of several enzyme systems (de- hydrogenases, proteinases and peptidases including carbonic anhydrase and alcohol dehydrogenase). |
| Iron (Fe) | As a constituent of various enzymes (cytochrome, catalase, dipeptides etc.), iron plays the part of a vital catalyst in the plant. It is a key element in various redox reaction of respiration and photosynthesis. |
| Manganese (Mn) | It is involved in the O evolving system of photosynthesis and it is a constituent of decarboxylases, kinases, oxidases etc. and hence, essential for respiration, formation of chlorophyll and reduction in nitrates. |
| Copper (Cu) | Acting as a component of metalloenzymes, regulating some enzymatic actions, and catalyzing oxidation reactions; Play ing a role in: i) nitrogen, protein and hormone metabolism; ii) photosynthesis and respiration. |
| Boron (B) | It is essential for development and growth of new cells in plant meristem. It is necessary for the germination of pol- len, formation of flowers and for the absorption of cations. |
| Molybdenum (Mo) | It’s function in rice plants is limited to the reduction of nitrate to nitrite. It is a component of nitrogenase, nitrate reductase, sulphate oxidase and xanthine hydrogenase enzymes . |
| Chlorine (Cl) | Essential for photosynthesis and as an activator of enzymes involved in splitting of water. Associated with osmoregulation of plants growing in saline soils. |
