Rice Disease 1

Bacterial blight

Bacterial blight is reported to reduced Asia’s annual production by as much. Bacterial blight is caused Xanthomonas campestris oryzae, an organism related to the bacteria bacterial leaf streak. The bacterium has races differ in their ability to the different resistant rice varieties.

Symtoms

Seedbed symptoms

In the seedbed, bacterial blight first causes tiny water-soaked spot on the margin of mature lower leaves. The spot enlarge, the leaves turn yellow, and dry and wilt.

Later season leaf symptoms

Lesion appear first, at about the heading stage, as water-soaked stripes on the leaf margin. Milky or cloudy dewdrop appear on the surface of young lesions in the morning. Bacterial ooze drops on young lesions. The lesion enlarge, the edges become wavy, and turn yellow or light brown. As the disease advances, the lesion cover the whole leaf blade, and turn grayish and later white.

Kresek symptoms usually occur 2-6 after the seedling stage.

Kresek symptoms sometime resemble rice stem borer damage

§ Leaves become water-soaked and fold and roll up along the midrib.

§ Then the whole plant wilts and dies.

o Distinguish kresek symptoms from rice stem borer , cut off the lower part the plant and squeeze it between fingers. A yellow bacterial ooze will appear the cut end if kresek is

o The yellow symptoms. Pale yellow occurs in the tropic, but is not common. Older leaves of infected plant are a normal green, but the youngest leaves are yellow or have a yellow stripe.

Disease cycle

After the initial leaf lesion appear, bacteria from ooze droplets on the leaf surface are spread throughout an area by wind and rain, particularly typhoons or irrigation water.

Rice plant can become infected with bacterial blight from many sources : diseased stubble, diseased seeds, paddy water, and diseased straw.

The bacteria enter through the water pores of the hydathodes or wounds of the leaf or root and multiply inside the plant.

The bacteria multiply inside the plant and enter the veins of leaf. Bacteria that enter the roots plug the water-conducting tissue and cause the plant to wilt.

* High temperature and humidity during crop growth increase the incidence of bacterial blight

The disease can survive in several species of weeds if rice not available

Control

The tropic, planting of resistant varieties is currently only practical way to control bacterial blight