Hosts and Symptoms
Peronosclerospora sorghi has a broad host range, particularly plants in the sorghum family. These host plants include Sorghum bicolor, or sorghum, Sorghum sudanense, or Sudan grass, and Sorghum palepense, or Johnsongrass. Its hosts also include Pinnisetum glaucum, or pearl millet, and Zea mays, or maize. When maize plants are infected as seedlings, the first symptom to appear is chlorosis of the leaves. As the plant grows, it often shows stunting, and necrotic lesions begin to form on the leaves. As the leaves continue to grow, a white, downy growth may develop in the necrotic lesions, especially on the underside of the leaves. This downy growth is the result of the production of conidia and conidiophores under the proper environmental conditions.
Sorghum and maize express very similar symptoms. In sorghum, chlorosis of the seedlings is very common after infection. As the leaves get older, they can express white striping, which eventually leads to the necrosis of the white striped tissue. When the leaves die, they begin to become shredded in appearance, similar to hail damage. This symptom is associated with the production of oospores in the leaf tissue.
If sorghum plants are young and produce conidia on their leaves, this type of infection often leads to the death of the plant. If the sorghum plants are older, the pathogen will often produce oospores in the leaves. Plants are usually capable of surviving this type of infection and will survive until maturity. The disease may cause the tassels and ears of maize plants to develop improperly or not form at all. This also occurs within the panicle of the sorghum plant.
Key factors in diagnosing downy mildew on maize and sorghum caused by Peronosclerospora sorghi include chlorosis of the leaves, followed by white streaking of the leaves. The leaves could also have a white, downy growth on the underside of the leaf blade. The white streaked areas of leaves become necrotic over time, leading to a shredded leaf appearance. In the maturing plant, the reproductive structures do not form properly or do not form at all. This leads to a sterile plant.
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