Zinc as an essential Plant Nutrient
There are 17 plants nutrients essential for growth, development and completing life-cycle of Plants i.e. seed to seed. Whenever their supply is restricted, deficiency symptoms are noticed on the plants in the form of leaves coloration or deformation of plant parts. Zinc is an important micro-nutrient along with other like Iron, Copper, Manganese, Boron, Molybdenum, Chlorine which are equally important in influencing crop yield as macro-nutrients but required in very small amount.
Role of Zinc :
Zinc regulates various metabolic activities and involved in production of growth regulating substances called Auxins in plants. Zinc is vital for photosynthesis and nitrogen metabolism. Zinc Deficiency affects flowering and fruit development by prolonging the vegetative period and delaying maturity resulting in lower yield with poor quality produce. In human beings zinc deficiency causes stunted brain development of the foetus. Infertility has also been observed in zinc deficient men. So zinc is very essential for both plants & human normal growth & development.
Zinc Deficiency Symptoms
Zinc deficiency symptoms start appearing after one month of sowing. The symptoms varies from light green, yellow to bleached spots in interveinal area of older leaves. The emerging leaves become smaller in size and internodal distance becomes short in case of severe deficiency. Deficiency system are prominent in Maize and Sugarcane that can be seen as yellow striping of leaves which becomes white in case of acute deficiency whereas Rice leaves becomes rusty. Cotton leaves also show bronzing of leaves whereas soybean plants are stunted with light green-yellow leaves. Zinc deficiency symptoms in some crops are briefly described below:
-
Citrus:
Small yellow blotches appear between the green veins on the leaves (mottle leaf). In case of severe zinc deficiency, the leaves become increasingly yellow except for the veins. Leaves are smaller than normal, narrow and have pointed tips. Maturity is delayed.
-
Cotton:
Symptoms appear three weeks after sowing. There is bronzing of both new and old leaves. Inter veinal chlorosis (golden yellow) is observed in the middle leave at initial stages of growth. The brown spots extend from the leave tip towards the base. Scorching of leaf margins occurs. The leaves have a tendency to cup upwards or downward. Leaves become thick and brittle and leaf margins turn upwards. Plant gets a bushy appearance due to shortened internodes. Fruiting is delayed.
-
Fruit Plants:
In Apple, plum, guava, peach, pear, and citrus, the leaf size at the shoot tip is greatly reduced (little leaf). The leaves become chlorotic (golden yellow) between the veins, while the veins remain green.
-
Maize:
Yellow striping of the leaves and older leaves have yellow streaks between the veins. In severe deficiency, the leaves show a broad yellow or entirely white band between midrib and edges. Young leaves are white and called the white bud in maize.
-
Mustard:
Inter veinal areas of the sub-terminal leaves develop light brown necrotic patches. These later enlarge and join to cover the entire leave blade except a narrow band along the veins.
-
Onion:
Plants are stunted with tops show marked twisting and bending.
-
Potato:
Zinc deficiency symptoms usually appear on the new growth. Zinc deficient plants show severe stunting and bronzing or yellowing of the leaves around margins starting from the tips. Youngest leaves are cupped upwards and resembles fern. Leaves of affected plants are smaller and their internodes are shorter than normal.
-
Pulses:
In greengram, blackgram, pigeon pea, and cowpeas, the veins and midrib of the old leaves remain green, the inter veinal portion develops a pale green or orange yellow colour. The leaves at later stages of growth, have reddish brown spots.
-
Rice:
Midrib of lower leaves towards the base becomes chlorotic. These leaves develop brown rusty spots which join together and form continuous areas. In case of severe deficiency, the entire leaf becomes rusty. Zinc deficiency in rice is termed as ‘Khaira’ disease in India. Symptoms is bronzing, starting with young leaves and later spreading to other leaves and stem.
-
Sugarcane:
White stripes/brands near the midrib 5-6 weeks after planting start near the base of lower leaves which spread towards the tip. At later stages, almost all the leaves show the deficiency symptoms.
-
Tomato:
Leaves show slow growth, become thick and show light inter-veinal chlorosis wilt and curl downwards. In later stages, older leaves turn brownish-orange with necrotic spots.
-
Vegetable Crops:
In chilies, okra and cucurbits, middle leaves show golden yellow or orange colour in the inter veinal portion while young leaves remain small in size.
-
Wheat:
Young leaves remain small, develop inter-veinal chlorosis and cup upwards. Middle leaves develop inter veinal chlorotic mottling and white necrotic lessons in the middle of the blade. The necrotic areas soon intensify and join together resulting in the collapse of the affected leaves near the middle. In case of severe deficiency, the lower leaves can be entirely chlorotic. Plants are stunted but unlike rice, bronzing is not very prominent.
