Question

what are the deficiency symptoms the role of phosphorus in plant

Answer 1

Growth may be reduced to less than one half that of well nourished plants, without the appearance of any identifiable symptoms of phosphorus deficiency. Mild phosphorus deficiency is often associated with a darker than normal, bluish green colour of the foliage. Unlike nitrogen deficiency, young to mature leaves remain dark green at all levels of severity. In a young crop, only severely stuntedplants will show obvious symptoms on the older leaves. However, on less severely deficient crops symptoms may develop as the crop matures.

The first sign of phosphorus deficiency is usually the premature senescence of older leaves. In most (but not all) cultivars, yellowing is preceded by the appearance of purple anthocyanin pigments, producing a range of autumnal colours in the senescing leaves. Yellowing may spread from discrete interveinal patches, which typically become cleared of anthocyaninpigment, or may be more general, but often affecting one half of the blade more than the other. In this case, the chlorotic areas may appear orange or red due to the overlying anthocyanin pigments. Necrotic lesions may develop in the chloroticzones, and the necroses spread as irregular patches until the leaf blade is entirely brown and dry. In some cultivars (eg. Markham) no yellow or purple phase precedes the necrotic lesions, which appear on green tissue. However, as in other cultivars, those parts of the leaf blade which are not yet necrotic turn yellow in the final stages of senescence.

Some cultivars may develop purple pigmentation on the upper surface of the youngest leaves, particularly on the veins. This may resemble nitrogen deficiency, although in phosphorus deficiency it is less common among cultivars, and is less strongly veinal.

Answer 2

Some crops, such as corn, tend to show an abnormal discoloration when phosphorus is deficient. The plants are usually dark bluish-green in color with leaves and stem becoming purplish.