Wheat yellow spot, also known as the disease caused by *Drechslera tritici-repentis*, is a common fungal infection affecting wheat crops. The symptoms primarily appear on the leaves, forming distinct yellow-brown spots that gradually expand into elliptical or spindle-shaped lesions. These lesions can range in size from 7 to 30 mm in length and 1 to 6 mm in width. The center of the lesions tends to be darker, while the edges are not clearly defined. In advanced stages, the spots may merge, causing the leaves to turn yellow and eventually dry out. This disease occurs in all wheat-growing areas and can cause significant yield losses if left unchecked.
The pathogen responsible for this disease, *Drechslera tritici-repentis* (formerly *Helminthosporium tritici-vulgaris*), is a fungus belonging to the genus *Aspergillus*. Its sexual stage is known as *Pyrenophora tritici-repentis*. The ascospores are colorless to yellow-brown, long and oval, with three septa, and measure between 42 to 69 μm in length and 14 to 29 μm in width. The asexual spores, or conidia, are pale to brownish, cylindrical, and often slightly curved. They have an obtuse tip and a pointed, snakehead-like base, with an umbilical depression. These conidia typically have 1 to 9 septa and range from 80 to 250 μm in length and 14 to 20 μm in width.
The disease spreads through infected seeds, crop residues, and contaminated soil. The pathogen survives the winter in plant debris or manure and infects wheat plants in the following growing season through ascospores. Once the disease appears, the infected tissues produce conidia, which are spread by wind and rain, leading to secondary infections and further disease development. Effective management includes crop rotation, proper sanitation, resistant varieties, and timely fungicide applications. Controlling this disease is crucial to maintaining healthy wheat crops and ensuring good yields.
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