Striga (Witchweeds) in Sorghum and Millet: Knowledge and Future Research Needs

Striga spp (witchweeds), are notorious root hemiparasites on cereal and legume crops grown in the semi-arid tropical and subtropical regions of Africa, the southern Arabian Peninsula, India, and parts of the eastern USA. These weed-parasites cause between 5 to 90% losses in yield; total croploss data have been reported. Immunity in hosts has not been found. Past research activities and control methods for Striga are reviewed, with emphasis on the socioeconomic significance of the species. Striga research involving biosystematics, physiological biochemistry, cultural and chemical control methods, and host resistance are considered. We tried to itemize research needs of priority and look into the future of Striga research and control In light of existing information, some control strategies which particularly suit subsistence and emerging farmers' farming systems with some minor adjustments are proposed. The authors believe that a good crop husbandry is the key to solving the Striga proble

Morphology Of Striga Forbesii And Preliminary Screening For Resistance In Sorghum

Striga forbesii Benth can be a serious pest problem on sorghum in Southern Africa. Its morphology, as found in the region, was described with the mention of a very small population on the species having an unusual floral form with strongly exerted style and stigma. It thus could be possible that there is some outcrossing in this predominantly autogamous species. The species produces up to 24,654 seeds per plant, and its seed production was compared with that of S. asiatica. Observation nursery screening showed that between 2.0 and 20.0 (%) germplasm accessions, from Zimbabwe, Botswana Swaziland, Lesotho and Angola, have resistance to S. forbesii. In addition, only 6.0 (%) from the Alad nursery and 3.2 (%) from the Karper nursery, which were introduced into the region, showed resistance. Preliminary results from advanced screening trials significant differential reactions to S. forbesii attack among sorghum varieties. Using the modified checkerboard design, five varieties, namely SAR 29, SAR 33, SAR 19, SAR 35 and SAR 37, showed good levels of tolerance of resistance to S. forbesii. The different reactions of susceptibility and resistance or tolerance were discussed relative to the test varieties

Comparative productivity and drought response of semi-tropical hybrids and open-pollinated varieties of sorghum

While the relative advantage of hybrids over open-pollinated varieties has long been established for temperate sorghums in developed countries, similar information for semi-tropical sorghums used in Africa and India is relatively scant, especially under conditions of drought stress. This study compared 23 hybrids with 21 open-pollinated varieties, all developed in India and/or Southern Africa. Materials were field-tested under conditions of stored soil moisture at two levels of drought stress (dryland or one supplemental irrigation) at Bet Dagan, Israel in 1989. Irrespective of the water regime, grain yield and harvest index increased and leaf area index decreased with a shorter growth duration of the genotypes. Hybrids were earlier, had a larger leaf area index, more than double the harvest index and produced more grain compared with varieties. In spite of their longer growth duration, varieties were less water-stressed than hybrids, as judged by their midday leaf water potential, relative water content and the extent of leaf rolling. The relatively poor plant water status of the hybrids could be partly ascribed to their larger leaf area index. Hybrids produced more biomass per day than varieties under low stress while varieties produced more biomass per day than hybrids under high stress. Thus, in terms of plant water status and mean daily biomass production, varieties were more drought resistant than hybrids. However, the physiological superiority of the varieties under drought stress did not result in a higher grain yield because of their inherent relatively poor harvest index, typical of the tall and late African sorghums. The superior physiological resistance to drought stress of these varieties could be translated into a yield advantage under drought stress if their potential harvest index is improved

Sorghum diseases in Eritrea - a survey report

Sorghum (Sorghum bicolor) is one of the main food crops of Eritrea. A total of 35 fields at 15 lowland locations and 13 fields at 8 highland locations planted with a variety of cultivars were surveyed in 2001 for sorghum diseases, based on the percentage of diseased plants in 5 subplots. In highland areas, covered kernel smut (Sporisorium sorghi [Sphacelotheca sorghi]) was predominant followed by head smut (Sporisorium reilianum [Sphacelotheca reiliana]) and about 10% incidence of Striga hermonthica. In lowland areas, leaf blight (Exserohilum turcicum [Setosphaeria turcica]), anthracnose (Colletotrichum graminicola [Glomerella graminicola]), zonate leaf spot (Gloeocercospora sorghi), loose kernel smut (Sporisorium cruentum) and covered kernel smut were important. Striga had between 2-100% incidence and was more prevalent in the drier lowlands. For all diseases, different cultivars exhibited different susceptibilities, and full results are tabulated

Major heretofore intractable biotic constraints to African food security that may be amenable to novel biotechnological solutions

The input costs of pesticides to control biotic constraints are often prohibitive to the subsistence farmers of Africa and seed based solutions to biotic stresses are more appropriate. Plant breeding has been highly successful in dealing with many pest problems in Africa, especially diseases, but is limited to the genes available within the crop genome. Years of breeding and studying cultural practices have not always been successful in alleviating many problems that biotechnology may be able to solve. We pinpoint the major intractable regional problems as: (1) weeds: parasitic weeds (Striga and Orobanche spp.) throughout Africa; grass weeds of wheat (Bromus and Lolium) intractable to herbicides in North Africa; (2) insect and diseases: stem borers and post-harvest grain weevils in sub-Saharan Africa; Bemesia tabaci (white fly) as the vector of the tomato leaf curl virus complex on vegetable crops in North Africa; and (3) the mycotoxins: fumonisins and aflatoxins in stored grains. Abiotic stresses may exacerbate many of these problems, and biotechnological alleviations of abiotic stress could partially allay some predicaments. Some of these constraints are already under study using biotechnological procedures, but others may require longer-term research and development to alleviate the problems. Despite the huge impacts of post-harvest weevils and of mycotoxins in grains, these issues had not been given high priority in national biotechnological programs, possibly due to a lack of knowledge of their immensity. The need for public sector involvement is accentuated for cases where immediate profits are not perceived (e.g. lowering mycotoxin levels in farmer utilized grain, which does not increase yield) but where the public weal will gain, and will be invaluable, especially where the private sector supplies genes already isolated

Improving the efficiencies of national crop breeding programs through region-based approaches: the case of sorghum and pearl millet in southern Africa

Resources available for agricultural research have fallen sharply in many national agricultural research systems (NARS) and international agricultural research centres. Therefore, it is becoming increasingly important that decision makers focus on improving the efficiency of national and international agricultural research. Breeding and variety release systems have remained largely focused on national challenges while seed markets are becoming globalized. This paper reports on studies and analyses of sorghum and pearl millet breeding and variety release systems conducted in Southern Africa Development Community countries. A synthesis is presented to provide a scientific and economic justification for improving the efficiency of the systems in SADC. It further proposes a regionalized breeding strategy that improves the efficiency in utilizing resources for crop breeding. Geographic information system analysis was used to delineate the region into four recommendation domains or agroecological zones (AEZs) based on length of growing period of the crop that cut across country borders. The AEZ together with multiple variety releases exemplify potential adaptability of the varieties across country borders. Sequential retrospective pattern analyses using grain yield data from multiple environment trials conducted over 12 years, stratified the 39 SADC test sites into 6 groups according to their similarity in line-yield. This provided an objective basis for selecting a few potentially useful and representative benchmark test sites for efficient regionalized variety testing in the future without loss of scientific information. NARS and International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) breeders have proposed a "Lead NARS" approach of regionalized breeding as a strategy for increasing the efficiency, cost effectiveness and sharing of regional responsibilities. Mechanisms for regionalized release procedures to facilitate farmer access to new improved varieties will alleviate problems of access to seed by farmers as well as the challenges facing small seed market

Trends and progress in sorghum research over two decades, and implications for global food security

Sorghum is a climate-resilient crop critical to livelihood in several semi-arid regions but has traditionally received limited research investment. In depth bibliometric analysis covering years 2000 – 2020 was performed using Scopus database to gain insight on sorghum research trends and identify gaps and opportunities for the crop. 17,720 relevant documents were retrieved and analysed. Robust increase in research literature on sorghum was observed for the period, more than tripling to almost 1,600/year in 2020. New opportunities stimulated by the sorghum genome sequencing and evolution of the crop as a model for drought tolerance, and growing recognition of sorghum as a potential food and energy security crop in response to climate change were key drivers of research output. Encouraging evidence demonstrates that both sorghum yield and nutritional quality are more stable to climate change compared to major cereal crops like maize and rice. End use trends suggest sorghum is more competitive in the food market than feed and bioenergy markets that have dominated its production in the past. Quality traits identified as most likely to expand long-term sorghum food value chain include endosperm functionality (kafirin protein properties), health (resistant starch and polyphenols), and nutrition (iron and zinc). Gene editing technology has shown promise as a tool to efficiently design sorghums with traits for high value food applications. Increased investment in market-driven sorghum improvement research targeting traits that address long-term consumer food needs will benefit both global food security and the environment