Abstract
A description is provided for Sclerospora graminicola. Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Pennisetum typhoides, Setaria italica, S. viridis (type), and other hosts: (?) Agrostis alba, Echinochloa crusgalli, E. crusgalli var. frumentacea, (?) Eleusine indica, Euchlaena mexicana, Panicum miliaceum, Pennisetum leonis, Saccharum officinarum (inoculation), Setaria lutescens, S. mugna, S. verticillata, Zea mays (particularly 'popcorn' but rare in general on maize). Green ear disease of Pennisetum typhoides[Pennisetum glaucum]. DISEASE: 'Graminicola downy mildew' of Gramineae. Symptoms vary according to host, time of their expression and ambient conditions. The disease is entirely systemic in pearl millet, most Setaria spp. and maize, with pallid continuous laciniate areas or stripes on leaf blades, starting at base of any leaf, being latent in plant before that and becoming more extensive on successive leaves; eventually oospores appear in chlorotic areas and leaves of Setaria, but not pearl millet or maize, shred. If symptoms start early, plants are severely stunted and chlorotic and may die: if symptoms are delayed, dwarfing may yet occur; some shoots may escape disease. White down (sporulation) appears on chlorotic areas before dawn if dews occur at night; sporangia are actively ejected and germinate immediately, producing zoospores, or else die within a few hours. Sporangiophores collapse. On maize there is a closed system of stripes on thickened, corrugated, brittle leaves. Tillering is excessive: the spike of pearl millet and occasionally the inflorescences of Setaria spp. and maize may be transformed into leafy growth ('green ear') with oospores within, sometimes with no other symptoms present. In S. magna and S. verticillata, linear chlorotic local lesions form and in S. italica occasionally spot-like lesions. GEOGRAPHICAL DISTRIBUTION Widespread (CMI Map 431, ed. 1, 1967; with additions and deletions here). Africa: all West Africa south of Sahara; Niger, Chad, Sudan, Egypt, Uganda, Tanzania, Mozambique, Malawi, Rhodesia, South Africa (all on pearl millet). Asia: Israel (on pearl millet, rarely maize), Iran (on Setaria glauca[Setaria pumila]) Pakistan, Khazakstan (on pearl millet), India (on pearl millet and Setaria spp.), northern China, Manchuria, Korea, Taiwan, Japan (on Setaria spp.). Europe: Spain, Southern France, Switzerland, Italy, Czechoslovakia, Germany, Hungary, Yugoslavia, Rumania, southern Russia, Ukraine, Caucasus (all principally or entirely on Setaria spp.). N. America midwestern and eastern USA, midwestern Canada and Ontario (on Setaria spp., rarely maize and Panicum). Oceania: Hawaii. The record on maize in Bulgaria and Argenlina as well as that on 'grass plots' with Ophiobolus in the Netherlands can undoubtedly be referred to Sclerophthora macrospora. TRANSMISSION: Initial infection is by oospores in soil, which may remain viable a number of years. Transmission by mycelial-infected seed reported (53, 2547) but most seed-borne infection is by oospore infestation. Oospores are still infective after passage through digestive system of cattle. Optimum temp, for infection of Setaria, 20-21°C, min. 12-13°C, max. 30°C. Optimum for sporangium production 25°C, min. c. 10°C (35, 602). Although zoospores from sporangia germinate, they have not been shown to induce infection under natural conditions (45, 3567; Safeeulla, 1970), except for local lesioning in a few species of Setaria, and the disease can be very severe in absence of high humidity and sporulation.
Geographical distribution of traits and diversity in the world collection of pearl millet [Pennisetum glaucum (L.) R. Br., synonym: Cenchrus americanus (L.) Morrone] landraces conserved at the ICRISAT genebank
