Rice blast disease| دھان کا بھبکا بیماری اور کنٹرول | Bemari ki pechan or control| cereal crop|Agri|

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دھان کا بھبکا یا بلاسٹ یا بھبکا‏
Magnaporthe grisea
بیماری کی پہچان
‏یہ بیماری ایک پھپھوندی کی وجہ سے ہوتی ہے۔ اس کا حملہ پتوں، گانٹھوں،
مونجر کی گردن اور مونجر پر ہوتا ہے۔ پتوں پر آنکھ جیسے نشان بن جاتے ہیں
جو دونوں اطراف سے نوکیلے ہوتے ہیں۔ اس کے کنارے گہرے بھورے
اور ان کا درمیانی حصہ مٹیالے رنگ کا ہوتا ہے۔ سازگار حالات میں یہ نشان بڑے ہو کر آپس میں
مل جاتے ہیں اور پتے کے بڑے حصے کو خشک کر دیتے ہیں، جس کی وجہ سے پتے کی خوراک بنانے کی صلاحیت بہت سست یا کم رہ جاتی ہے۔‏
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‏یہ بیماری نمی والے موسم میں جب بارش زیادہ عرصہ رہے اور سورج نہ نکلے تو خوب پھیلتی ہے۔ نیز بارش جس کا دورانیہ کم ہو اس بیماری کے پھیلاؤ میں معاون نہیں ہوتا۔ زیادہ نائٹروجنی کھاد کے استعمال سے بھی اس بیماری کا احتمال بڑھ جاتا ہے۔ یہ بیماری کٹائی کے بعد متاثرہ فصل کی مڈھ اور پرالی پر باقی رہ جاتی ہے۔
DISEASE: Rice Blast
PATHOGEN: Magnaporthe oryzae (anamorph: Pyricularia oryzae)
HOSTS: Rice (Oryza sativa).
Hundreds of millions of people world-wide depend on rice as a staple food (Figures 1, 2). A crop failure, for any reason, poses a real threat of starvation. Rice blast, caused by a fungus, causes lesions (Figure 3) to form on leaves, stems, peduncles, panicles, seeds, and even roots. So great is the potential threat for crop failure from this disease that it has been ranked among the most important plant diseases of them all. Other grasses, including crabgrass, are infected with closely related fungi (Magnaporthe grisea, Magnaporthe poae, Magnaporthe rhizophila and Magnaporthe salvinii), which cause nearly identical symptoms on their respective hosts.
Symptoms and Signs
The symptoms of rice blast include lesions that can be found on all parts of the plant, including leaves, leaf collars, necks, panicles, pedicels, and seeds. A recent report shows that even roots can become infected. However, the most common and diagnostic symptom, diamond shaped lesions, of rice blast occur on the leaves, whereas lesions on the sheaths are relatively rare.
Rice leaves. The symptoms on leaves may vary according to the environmental conditions, the age of the plant, and the levels of resistance of the host cultivars (Figure 4). On susceptible cultivars, lesions may initially appear gray-green and water-soaked with a darker green border and they expand rapidly to several centimeters in length. On susceptible cultivars, older lesions often become light tan in color with necrotic borders. On resistant cultivars, lesions often remain small in size (1-2 mm) and brown to dark brown in color.
Rice collars. The collar of a rice plant refers to the junction of the leaf and the stem sheath. Symptoms of infection of the collars consist of a general area of necrosis at the union of the two tissues (Figure 5). Collar infections can kill the entire leaf and may extend a few millimeters into and around the sheath. The fungus may produce spores on these lesions.
Rice necks and panicles. The neck of the rice plant refers to that portion of the stem that rises above the leaves and supports the seed head or panicle. Necks are often infected at the node by the rice blast fungus and infection leads to a condition called rotten neck or neck blast (Figure 6). Infection of the necks can be very destructive, causing failure of the seeds to fill (a condition called blanking) or causing the entire panicle to fall over as if rotted. The rice blast fungus can also infect the panicles as the seeds form (Figure 7). Lesions can be found on the panicle branches, spikes, and spikelets. The lesions are often gray brown discolorations of the branches of the panicle, and, over time, the branches may break at the lesion.
Rice seeds. The fungus has often been isolated from the pedicels of the seeds. Seeds are not produced when pedicels become infected, a condition called blanking. Symptoms of rice blast on seeds themselves consist of brown spots, blotches (Figure 8), and occasionally the classic diamond-shaped lesion often seen on leaves. The process and the time during which infection of seeds by spores of the pathogen occurs has not been fully described but recent information shows that the fungus can infect seeds by infecting the florets as they mature into seeds, and it is believed that this is the main way seed infection develops.

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