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Yellow leaf blight disease typically starts from the lower leaves and progresses upward. Affected leaves turn yellow, then dry and become white. Initially, dark green spots appear at the leaf tip or edge, which develop into yellow, elongated stripe lesions. The boundary between diseased and healthy tissue is distinct, and the leaves often show a corrugated appearance. In later stages, small, jelly-like structures appear on the leaf surface. When diseased leaves are cut and placed between two glass slides, and clear water is dripped onto them, bacterial exudation can be observed.
Yellow dwarf disease usually begins in the parietal lobe and the next 1–2 leaves, then spreads upward and downward. The leaves gradually turn yellow or develop a mottled mosaic pattern. Infected plants are stunted, with shortened internodes and an abundance of black roots. New root development is reduced, and the leaves become flat, wavy, and often yellow and dry.
Physiological premature aging and fertilizer damage can also cause yellowing of rice leaves, and these conditions need to be differentiated. Physiological yellowing starts from the lower leaves and spreads upward, with the leaves showing an orange-yellow color and a metallic sheen. There are no visible lesions or bacterial masses present. Improper use of ammonium bicarbonate, ammonia, or pesticides may lead to yellow or golden yellow discoloration, sometimes accompanied by burning-like spots.
In acute rice blast, the lesions begin as small dark brown spots that later become oval with grayish-green mold on their back. In the chronic form, the lesions are fusiform with reddish-brown borders and a gray center. A brown necrotic line runs through the middle of the lesion. When wet, a gray-green mold layer becomes visible on the back of the lesion.
The flax patch disease starts as small, needle-like spots that gradually expand into oval-shaped lesions resembling sesame seeds. The thickened lesions are dark brown and darker than those caused by rice blast. Closer inspection reveals three distinct color layers: an outer yellow halo, a wide dark brown edge, and a central area that is mostly gray and yellow. The dark brown part of the lesion appears lighter when viewed from above and often obscures the fine vein network. No necrotic lines are present on either side of the lesion.
Bacterial brown stripe disease initially affects the midrib at the base of the leaf, spreading both upward and downward, forming brown stripes. The affected areas exude a milky white liquid. As the disease progresses, the plant rots and emits a foul odor. Dead leaves remain attached, and the heart leaves die and become brittle.
Pediococcus pneumoniae often appears in clusters, affecting multiple strains within the field. The basal tissues of rice plants become soft and develop dark brown spots. The most distinctive feature is the peeling of the leaf sheaths and stalks. Many small, black sclerotia, smaller than leek seeds, are present.
Bacterial base rot occurs sporadically in the field, with one to three infected plants per spot. The base of the affected plant shows a gray, rotten appearance. The plant can be easily pulled out of the soil, and when squeezed, a milky white, cloudy bacterial fluid oozes out, accompanied by a strong odor. No fungal structures are present.
Physiological blue-green stem discoloration causes the stems to shrink, become dry, and prone to lodging. The base of the stems shows no signs of insect damage or lesions. Aseptic nuclei may appear in the sheaths and stalks, especially in late rice varieties nearing maturity.
In cases of dry heart locust, wormholes or insect frass can be seen in the lower parts of the rice plant. The dead heart is easy to pull up. In indica rice, there are no wormholes or insects in the stems. The dead heart strains are easily removed, and the stem base and roots are shredded.
Diseased stripe plants show yellow streaks on the leaves, which curl into a paper-like shape and droop, forming a "false dead heart." The base has no wormholes, does not rot, and the dead heart is difficult to remove.
In white panicle rice, insects or worms can be found in the upper parts of the stems, and the white panicles are easy to pull up. The panicles and necks are not affected, and the white panicles are clearly visible in the field.
For panicle and japonica rice, there are no wormholes in the stems, and the white panicles are not easily removed. Dark brown spots appear on the neck, cob, and branches. These parts are easily broken. When wet, gray-green spores are visible on the diseased areas.
Rhizoctonia solani appears on the leaf tips, leaves, or heads, stems, and stalks. Initially, dark green spots form, which later expand into oval, cloud-like lesions with brown edges and a light brown to grayish-white center. The base tissue becomes soft, and the white panicles fall flat.