Tuesday, June 14, 2011

Rice Diseases

Rice crop can be infected by living pathogens(fungi, bacteria, virus and nematodes) which cause infectious diseases or may also be damaged by some physical factors (rise or decrease in temperature, unavailability of water ) which cause noninfectious diseases. Apart from the fact weather the disease is infectious or noninfectious, any disease causes reduction in yield, so you can't ignore the diseases at any stage. The most important diseases of rice in various rice growing area of world are brown spot, blast, stem rot, bunt, bacterial blight, false smut, ufra and khaira (zinc deficiency). Blight or Brown Spot diseases is cause by fungal pathogen Helminthosporium oryzae in this disease, small oval shaped spots appear on the leaves which after few days join with each other and form linear spots. Later on, the leaves become yellow and poor germination occur. Another sever disease is the Bunt of Rice or Smut caused by Tilletia barclayana. In this disease, the grains filled with black powdery mass of fungus. Mostly a few number of grains are infected in an ear and if these are not severely infected, they can germinate but the seedlings show stunt in growth. Rice Blast caused by Pyricularia oryzae is another infectious disease in which fungal pathogen cause small, water soaked whitish, greyish or bluish spots on leaves, grains and on nodes. Brown spot may also be developed on plant. when the mature stage of fungal development reach the spot blasted. Grain development affected. In Bacterial Blight of Rice cause by Xanthomonas oryzea water soaked stripes appear along the margin of leaf blades, which later on enlarge and turn yellow. These lesions may cover the entire blade, may extend to the lower end of leaf sheath. Similar symptoms may occur on glumes of green grains.In Stem Rot (sclerotium oryzae) of Rice two to three months old plants begin to wither and ultimately dry up; the sheaths soon turn somewhat dark and start rotting. Black dots (fruiting bodies of sclerotia) occur at the base of dried leaves and leaf sheaths. Stem begins to rot and become soft, plant falls down.

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