Area under cultivation, production and yield per
hectare of rice indicates its importance. It is one of the leading food
crops of the world and a cash crop of Pakistan. It contributes 15 per
cent to the foreign exchange earnings.
The rice is frequently grown on heavy clay soils that
have an impervious, subsoil layer (hard pan) that limits the drainage,
because it requires a constant and plentiful supply of water. The rice
production can be used to reclaim saline soils, because flooding leaches
salts from the soils.
In those areas, where other crops are not possible to
grow or where Kharif irrigation water supply is abundant, this crop is
very suitable. Rice plants prefer 5.0-6.5 soil pH, and are moderately
tolerant to exchangeable sodium percentage (ESP) in the level of 20-40
per cent. This crop may also tolerate up to 0.40-0.60 per cent of the
white alkali and 0.10-0.20 per cent of the black alkali in the soil.
The rice crop is subjected to more than 40 diseases,
which are one of the reasons for the low yields of rice in the world,
The fungi, bacteria, nematode and the virus cause
different infectious diseases. Non-infectious diseases may be caused
because of low or high temperature, decrease or increase in different
nutritional elements essential for the crop. The causes of fluctuation
in the production may be more, but the diseases could not be ignored,
neglected or regretted, because they also cause variable loss of time to
The diseases may appear at any stage of the growth
and development of plant, attacking the seed sown, root system, foliage,
stalk, leaf sheath, inflorescence and even the developing grain. All
these diseases are injurious in some areas, in different years and on
various parts of the plant. All parts of plant are subject to disease
and one or more diseases can occur on virtually every plant and in every
field. These all draw attention because of the symptoms or signs and
generate great concern because of their effects on the quality or the
quantity of plants, straw and grains.
The brown spot, blast, stem rot, bunt, bacterial
blight, false smut, ufra and khaira (zinc deficiency) are sometimes
considered important diseases at various parts of the rice growing areas
of world including Pakistan. The brown spot or blight of rice is a much
more widespread and a common disease in almost all rice growing areas of
the world. Therefore cause, symptoms (identification), perpetuation
(survival from season to season), transmission and control (disease
management practices) of this most important disease of rice is being
summarized, so that the growers may protect their crop, the research
workers may decide their future strategies and extension workers may
also become alert.
The disease has been recorded all over the country.
Initially small dots or circular eye-shaped or round to oval spots
appear in light colour on the leaves. These spots increase in size,
coalesce with each other and result in linear spots brown in colour on
diseased leaves. Later on the withering and the yellowing of leaves
occur. Similar symptoms appear on glumes and kernels. The seed setting
may also be affected, cause sterility, shrivelling and shows rotting and
poor germination. Mostly emerged seedlings become blighted, if the
disease is severe.
The diseased seeds, plant debris and soils of
infected crop help the fungus to survive. In our conditions, the disease
causing fungus mostly survive and multiply on diseased crop debris lying
in the field as well as on the certain grasses and weed plants, from
which the organism can pass to regular rice crop under favourable
conditions. Air and irrigation water helps the fungus in transmitting
from the diseased to healthy plants.
The following disease management practices are proved
to be the best for control of brown spot or blight of rice:
The use of resistant varieties or disease-free seed in healthy soils.
Sanitation and crop
Hot water seed treatment at 54C for 10 minutes or with seed dressing
Collection and destruction of stubble and spraying with copper
fungicides at right time.
Application of suitable foliar fungicides help to minimize further
dissemination of the disease.
Improving drainage system is reported beneficial.
Fulfilment of nutritional requirements of plants, mostly in poor soils,
increase disease resistant.