Symptoms: Symptoms often vary as a result of systemic infection. Leaf symptoms begin as chlorosis at the base, and successively higher leaves show progressively greater chlorosis. Infected chlorotic leaf areas can support abundant white asexual sporulation on the lower leaf surface. Severely infected plants are generally stunted and do not produce panicles. Green ear symptoms result from transformation of floral parts into leafy structures.
Pathogen and disease characteristics: Asexual sporangia are produced during the night under moderate temperatures and high humidity. Optimum sporangium production occurs at 20 °C. No sporulation below 70 percent relative humidity. Sporangia germinate to liberate 1 to 12 zoospores, which encyst and germinate by germtube. Sporangia generally do not remain viable very long after daybreak. Sexual oospores are thick-walled, spherical, brownish yellow, and 22 to 35 µm in diameter. Oospores form in colonized plant tissue and can survive from 8 months to 13 years under laboratory conditions.
Host range: Pearl millet. Host specificity is important in determing host range for this pathogen. S. graminicola has been reported from maize, sorghum, Echinochloa crus-galli, Panicum miliaceum, Pennisetum leonis, P. spicatum, Setaria italica, S. lutescens, S. verticillata, S. viridis, S. magna, Euchlaena maxicana, and Agrostis alba. Cross-inoculation studies to different hosts have usually been unsuccessful when attempted.
Geographic distribution: On page 2 of the primary citation, a reference to a 1884 publication by Farlow indicates that S. graminicola has been identified in the United States on "other millets." On page 3, the continental U.S. is included in the geographic distribution of the pathogen. Despite this information,
THIS PATHOGEN HAS NOT BEEN REPORTED ON PEARLY MILLET IN THE UNITED STATES, AND ALL EFFORTS TO RESTRICT ITS ENTRY SHOULD BE CONTINUED.
Sclerospora graminicola has been reported on pearl millet in the countries listed below:
Africa: Chad, Egypt, Gambia, Malawi, Mozambique, Niger, Nigeria, Senegal, South Africa, Zimbabwe. Also Burkina Faso, Ghana, Ivory Coast, Kenya, Mali, Sudan, Tanzania, Togo, Uganda, Zambia (S.B. King, personal communication, 1995).
Asia: India, Pakistan. Also Israel (S.B. King, personal communication, 1995).
Alternative disease name: Green ear disease.
Seed transmission: Evidence for transmission by seed is inconsistent and controversial. It has been suggested that this disease can be transmitted by oospores on the seed surface. To prevent introduction of S. graminicola, seed treatment is recommended.
Primary citation: Singh et al. 1993.
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Original posting: June 5, 1999.