Wheat yellow spot, also known as the disease caused by *Drechslera tritici-repentis*, is a common fungal infection that primarily affects wheat leaves. The symptoms typically appear as small, yellow-brown spots that gradually expand into elliptical or spindle-shaped lesions, ranging in size from 7 to 30 mm in length and 1 to 6 mm in width. These lesions often have a dark center with no distinct borders, and in later stages, they may merge together, causing the leaves to turn yellow and eventually dry out. This disease can occur in all wheat-growing areas and can lead to significant yield losses if left unchecked.
The pathogen responsible for this disease, *Drechslera tritici-repentis* (formerly known as *Helminthosporium tritici-vulgaris*), is a fungus belonging to the genus *Aspergillus*. Its sexual stage is referred to as *Pyrenophora tritici-repentis*. The ascospores are colorless to yellow-brown, long-oval in shape, and contain three septa, with 0 to 1 median septum. Their size ranges from 42 to 69 μm in length and 14 to 29 μm in width. The asexual spores, or conidia, are pale to brownish, cylindrical, and slightly curved, with an obtuse tip and a sharp, snakehead-like base. They may have between 1 to 9 septa and measure 80 to 250 μm in length and 14 to 20 μm in width.
The disease spreads through various routes, including infected seeds, crop residues, and contaminated soil or manure. During winter, the pathogen survives in these materials and becomes active the following growing season when ascospores are released. Once the disease starts, infected plant parts produce conidia, which are then spread by wind and rain, leading to secondary infections and further disease development. Proper management practices, such as crop rotation, resistant varieties, and timely fungicide applications, are essential in controlling this disease. For more detailed control methods, refer to the section on wheat leaf spot and root rot management.
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