Xenognosin production and tolerance to Striga asiatica infection of high-yielding maize cultivars

Ten cultivars of maize, a number of which are high yielding in the presence of the weed Striga asiatica in sub-Saharan Africa, were tested for resistance and tolerance to this root hemiparasite. Observed in rhizotrons, Striga asiatica attached and developed on roots of all cultivars, indicating that none exhibited a true resistance mechanism. However, root exudates from two cultivars, IWD STR Co and Zea diploperennis BC4C2, stimulated relatively little germination of S. asiatica, indicating low xenognosin production, with few parasites attaching and no significant decrease in host height or biomass apparent after 55 days of infection. Cultivar 98 Syn WEC also exhibited no significant differences in height and biomass on infection despite high xenognosin production and a lack of resistance to parasite attachment and development, indicating the operation of a tolerance mechanism. Cross-breeding of these low xenognosin-producing maize cultivars and Striga-tolerant lines could produce cultivars that perform exceptionally well on Striga-infested soils. This study highlights the need for cereal breeders to distinguish between the different mechanisms underpinning host performance in the presence of Striga

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

Nutritional quality and utilization of local and improved cowpea varieties in some Regions in Tanzania

Cowpeas are grown for their leaves and grains both of which are used as relish or side dishes together with the staple food. Little information is available on the nutritional quality of local and improved cowpea varieties grown in Tanzania as well as the recipes in which they are ingredients. This study was done to investigate cowpea utilization in Iringa and Dodoma regions of Tanzania. A cross-sectional survey was carried out where a total of 517 farmers were interviewed using a pre-tested structured questionnaire. Proximate and mineral composition of different varieties of cowpea grains and leaves were determined using standard AOAC methods. More than half of the households interviewed consumed cowpeas in one or more forms. Most cowpea recipes included them as relish being eaten with rice or stiff porridge (ugali), a mixture of dehulled maize and cowpea grains (kande) and cowpea buns (bagia). Improved cowpea varieties had relatively higher fat content ranging from 8 to 11.2% compared to local varieties (5.4%). Local cowpea grains had higher levels of calcium varying between 958.1 and 992.4 mg/kg than dehulled cowpea (360 to 364 mg/kg) and cowpea flour (303 to 311 mg/kg). Zinc ranged from 32.6 to 31.5 mg/kg, while iron content ranged from 27.6 to 28.9 mg/kg. Fresh cowpea leaves had the highest levels of minerals, with calcium varying between 1800.6 and 1809.6 mg/kg, zinc between 36.1 and 36.0 mg/kg and iron between 497.0 and 499.5 mg/kg. The improved cowpea varieties, IT99K-7212-2-1 (23.8 mg/kg) and IT96D-733 (21.2 mg/kg) had the highest iron content. IT99K-7-21-2-2-1 (32.2 mg/kg) and IT97K499-38 (28.3 mg/kg) had the highest zinc concentration. The bagia (cowpea buns), prepared in Dodoma had higher mineral composition, calcium (893mg/kg), zinc (13.7 mg/kg) and iron (16.3 mg/kg) compared to those prepared in Iringa; calcium (32.6mg/kg), zinc (4.96 mg/kg) and iron (5.2 mg/kg). The cowpea daily per capita consumption for the majority of the households surveyed ranged from 41 to 200 gm. The contribution of micro and macro nutrients is significant for both developed lines and local varieties but with leaves having greater mineral content than the grains; hence, promotion of consumption of the leaves alongside the grains would be of nutritional advantage. Additionally, farmers should be encouraged to plant the higher yielding cowpea varieties and preferred local varieties

Optimal environmental conditions for the infection and development of Puccinia purpurea on sorghum

Although rust can reduce grain yields of late-planted sorghum crops in Queensland, little research has been conducted on environmental parameters affecting infection and development. The effects of temperature, leaf wetness period, plant growth stage, urediniospore concentration and darkness period on the development of rust (Puccinia purpurea) on the inbred Sorghum bicolor line IS8525 were evaluated separately by artificial inoculation of plants under controlled conditions. Rust developed between 16 and 28 °C, with the optimum temperature being 20 °C. Disease severity (pustules cm−2) increased as the length of leaf wetness increased from 4 to 24 h. Infection occurred when plants were exposed to full light, full darkness and varying periods of darkness for the first 24 h after inoculation; 16 h of darkness resulted in the highest rust severity. Plants of IS8525 and of the more resistant line IS12539 inoculated 21–49 days after sowing developed higher levels of rust than others inoculated at, or close to, flowering (63 days after sowing). Rust severity also increased with increasing urediniospore concentrations, but leaf death occurred on young plants inoculated with the highest concentration (50 mg 100 mL water−1). The findings of this study have been used to develop an inoculation technique to detect putative pathotypes of P. purpurea in Australia