Sorghum and Millets Diseases A Second World Review

This book is the product of an international workshop held at Harare, Zimbabwe, in Mar 1988. Progress made on sorghum diseases since the first global workshop held in India in 1978 is reviewed; research needs and goals for the next decade are identified; and the strengthening of working relationships among pathologists studying sorghum and millets diseases discussed. Also included are recommendations made by workshop participants and reports on group discussions

Secondary conidiation of Sphacelia sorghi on sorghum, a novel factor in the epidemiology of ergot disease

Sphacelia sorghi, the ergot pathogen of sorghum in Zimbabwe, causes copious exudation of honeydew containing macroconidia. Within a few days the exudate develops a white crust consisting of a layer of secondary conidia borne above the honeydew surface on a palisade of sterigma-like projecting hyphae which arise from the macroconidia immediately below the honeydew surface. Secondary conidia are windborne, initiate infection and are recognized for the first time to have an important role in the epidemiology of ergot disease of sorghum in Southern Afric

Claviceps africana sp. nov.; the distinctive ergot pathogen of sorghum in Africa

Stromata arising from ergot sclerotia from sorghum in Zimbabwe were different in colour and texture from those of Claviceps sorghi from sorghum in India, compounding other differences in the dynamics of the early stages of parasitism, the sugar composition of honeydew, the quantitative expression of secondary conidiation and the morphology of sclerotia. The distinctive sexual stage forms the basis of describing the African material as a new Claviceps species which also uniquely elaborates a group of dihydrogenated ergot alkaloids that are biosynthetic intermediates leading to the principal product dihydroergosin

Windborne spread of ergot disease (Claviceps africana) in sorghum A-lines in Zimbabwe

In field trials in Zimbabwe, C. africana spread rapidly through replicated plots of male-sterile sorghum A-lines, from a group of centrally situated, inoculated plants. Prominent secondary conidiation by the pathogen on the surface of exuded honeydew provided airborne spores which were trapped in a Burkard continuous spore trap and showed diurnal peaks in air close to the primary inoculum source. From the rate and pattern of disease spread it is concluded that the characteristic secondary conidia of C. africana were the principal disease agents within the experimental area, and that ergot spread by windborne secondary conidia has significant epidemiological and economic implications for sorghum hybrid breeding in southern Africa

Influence of primary weather variables on sorghum leaf blight severity in Southern Africa

A study was conducted on the effect of climatic factors (rainfall, min. and max. air temp.) on severity of leaf blight (Exserohilum turcicum [Setosphaeria turcica]) over several locations and years in southern Africa (Malawi, Swaziland, Tanzania, Zambia, Zimbabwe). The weather data used were from 2 weeks before sowing to 3 weeks after sowing. Temp. was the most important variable predicting disease severity after dough stage of the crop. High disease severities coincided with min. temp. between 14 and 16°C and mean temp. of 20.8-22.2°. Low severity at dough stage of the sorghum or absence of leaf blight was associated with min. temp. >16° from 2 weeks before sowing to 3 weeks after sowing. Discriminant analysis conducted using temp. from very early in the season correctly classified 88% of the cases into 3 disease severity categories: no, low and medium-high disease. It is concluded that, primary weather variables, in particular air temp., may be valuable predictors of disease severity early in the season. The results may be used to identify and map disease levels for large areas using past temp. dat

Diseases and parasitic weeds of sorghum in Tanzania: Occurrence and incidence, 1986-1990

Sorghum is an important subsistence crop in Tanzania. Surveys were carried out between the 1986 and 1990 crop seasons to determine the prevalence of diseases and parasitic weeds in the major sorghum-growing areas of Tanzania. Twenty diseases of sorghum and three parastic weeds were observed. Grain moulds (several fungi), grey leaf spot (Cercospora sorghi), anthracnose (Colletotrichum graminicola), rust (Puccinia purpurea), leaf blight (Exserohilum turcicum), ladder leaf spot (Cercospora fusimaculans), sooty stripe (Ramulispora sorghi) and zonate leaf spot (Gleocercospora sorghi), were economically important diseases. Striga asiatica was the most common parasitic weed in Tanzania. Ilonga in the low-altitude (⩽ 1000 m) zone and Hombolo in the mid-altitude (> 1000 m) zone were identified as locations with a high frequency of diseases and striga incidence. These locations were recommended for resistance screening against most of the leaf diseases, grain moulds and S. asiatica

Brown leaf spot of pearl millet caused by Bipolaris urochloae in Zimbabwe

A leaf spot disease of pearl millet (Pennisetum glaucum [P. americanum]), characterized by the presence of extremely variable symptoms ranging from small dots or flecks to large, rectangular or spindle-shaped spots, was caused by B. urochloae. The disease was observed at several locations in Zimbabwe during 1985-87. Limited observations suggest that the disease is potentially important. This is the first report of B. urochloae attacking P. americanu