Many environmental factors constrain the production of major food crops in Sub-Saharan Africa and South Asia. At the same time, these food production systems themselves have a range of negative impacts on the environment. In this paper we review the published literature and assess the depth of recent research (since 2000) on crop x environment interactions for rice, maize, sorghum/millets, sweetpotato/yam and cassava in these two regions. We summarize current understandings of the environmental impacts of crop production systems prior to crop production, during production and post-production, and emphasize how those initial environmental impacts become new and more severe environmental constraints to crop yields. Pre-production environmental interactions relate to agricultural expansion or intensification, and include soil degradation and erosion, the loss of wild biodiversity, loss of food crop genetic diversity and climate change. Those during crop production include soil nutrient depletion, water depletion, soil and water contamination, and pest resistance/outbreaks and the emergence of new pests and diseases. Post-harvest environmental interactions relate to the effects of crop residue disposal, as well as crop storage and processing. We find the depth of recent publications on environmental impacts is very uneven across crops and regions. Most information is available for rice in South Asia and maize in Sub-Saharan Africa where these crops are widely grown and have large environmental impacts, often relating to soil nutrient and water management. Relatively few new studies have been reported for sorghum/millets, sweetpotato/yam or cassava, despite their importance for food security on large areas of marginal farmland in Sub-Saharan Africa – however, there is mounting evidence that even these low-input crops, once thought to be environmentally benign, are contributing to cycles of environmental degradation that threaten current and future food production. A concluding overview of the emerging range of published good practices for smallholder farmers highlights many opportunities to better manage crop x environment interactions and reduce environmental impacts from these crops in developing countries.

/pdf/environmental-impacts-and-constraints-associated-with-the-5bwtx9yjlr.pdf

Environmental impacts and constraints associated with the production of major food crops in Sub-Saharan Africa and South Asia

Cassava (Manihot esculenta Crantz.) is the most important vegetatively propagated food staple in Africa and a prominent industrial crop in Latin America and Asia. Its vegetative propagation through stem cuttings has many advantages, but deleteriously it means that pathogens are passed from one generation to the next and can easily accumulate, threatening cassava production. Cassava-growing continents are characterized by specific suites of viruses that affect cassava and pose particular threats. Of major concern, causing large and increasing economic impact in Africa and Asia are the cassava mosaic geminiviruses that cause cassava mosaic disease in Africa and Asia and cassava brown streak viruses causing cassava brown streak disease in Africa. Latin America, the center of origin and domestication of the crop, hosts a diverse set of virus species, of which the most economically important give rise to cassava frog skin disease syndrome. Here, we review current knowledge on the biology, epidemiology, and control of the most economically important groups of viruses in relation to both farming and cultural practices. Components of virus control strategies examined include: diagnostics and surveillance, prevention and control of infection using phytosanitation, and control of disease through the breeding and promotion of varieties that inhibit virus replication and/or movement. We highlight areas that need further research attention and conclude by examining the likely future global outlook for virus disease management in cassava.

Cassava Virus Diseases: Biology, Epidemiology, and Management

To shed light on trends about elimination of viruses from plants, a bibliographic research was conducted to identify thermotherapy, chemotherapy and tissue culture trials published from 1991 through 2010. Among woody plants, grapevine, apple and peach are the most frequent targets of sanitation protocols because their health status is strictly regulated. Even if thermotherapy represents the preferred method for the host, grapevine viruses can also be eliminated with chemotherapy and tissue culture; apple viruses respond to chemotherapy as well. Although a similar trend was reported among herbaceous plants, chemotherapy was the most frequently used technique in potato. With regard to virus, thermotherapy was successfully applied against viruses belonging to 13 families and an unassigned genus. Instead, chemotherapy and tissue culture techniques eradicated viruses belonging to fewer families (nine). An interpretation of thermotherapy effects considers the new metabolic “pathways” triggered by the natural antiviral response emitted by the infected plant, with particular reference to virus-induced gene silencing. With regard to chemotherapy, several groups of antiviral drugs belong to inosine monophosphate dehydrogenase inhibitors, S-adenosylhomocysteine hydrolase inhibitors, neuraminidase inhibitors. Tissue culture, usually adopted to regenerate plantlets in biotechnological breeding programs, represents the less used tool for eliminate viruses from plants.

https://dialnet.unirioja.es/descarga/articulo/4183676.pdf

Review. Elimination of viruses in plants: twenty years of progress

Management of plant virus and viroid diseases is a matter of vital importance and concern to the farmer, horticulturist, forester and gardener. It is well established that the virus and viroid diseases in different crops cause enormous losses in terms of quantity and quality of products (see Chapter-3 of Volume-I) (Sastry 2013b). Because of the serious losses they cause to agriculture and horticulture, virus/viroid diseases have acquired great importance in the realm of plant pathology and call for effective management measures against them. These diseases are not amenable to control by direct methods. Unlike fungicides and bactericides, no commercial viricides have yet been developed. However a number of indirect control measures for different crop plant-virus/viroid pathosystems suitable to varied agro ecosystems have been developed with an aim to avoid the pathogen or to minimize their impact on crop yields (Thresh 2003, 2006). As these diseases routinely cause systemic infections and have very effective methods of transmission, preventing their spread has become a complicated problem. Some diseases like Tobacco mosaic virus (TMV), Potato virus X (PVX), Cucumber green mottle virus (CGMMV), Citrus exocortis viroid (CEVd) and Potato spindle tuber viroid (PSTVd) are highly contagious and affect large number of hosts belonging to several families.

Management of Virus and Viroid Diseases of Crops in the Tropics

Sweetpotato (Ipomoea batatas L. Lam) is a tuber crop of immense potential as it produces more edible energy on marginal land than any other major food crop. As well as this useful property it can withstand adverse abiotic and biotic stresses and does not require intensive care. It therefore plays an important role in the economy of poor households where it acts as a major source of subsistence and is considered to be a ‘famine relief crop’. Besides this important function, the crop has immense industrial value for extraction of starch and production of animal feed. For all these reasons sweetpotato has great possibilities for enhancing food and nutrition security in developing and underdeveloped countries where most of the farmers’ holdings belong to the small and marginal categories. Although the crop is assuming greater significance owing to the ever-increasing population its importance is still underestimated and, unlike most staples, fails to attract sufficient attention of agricultural researchers throughout the tropics and subtropics. With greater attention and more collaborative research, there could be considerable improvements in the genetics of the crop and its husbandry which, together, would allow it to fulfill a wide range of needs in these areas of the world.

Crops that feed the world 5. Sweetpotato. Sweetpotatoes for income and food security

A survey was conducted on the incidence of cassava mosaic disease (CMD) in Kerala. Cassava mosaic disease occurred throughout the state at low to high incidences (44.5-96.75%) in the 35 regions surveyed. The disease incidence was higher in Thiruvananthapuram and Kollam districts and lower incidence was noticed in Wayanad district. Maximum white fly population was also observed in Thiruvananthapuram district of Kerala followed by Kollam. Survey results alsoindicate that Sri Lankan Cassava Mosaic Virus (SLCMV) is wide spread in Kerala.

http://www.isrc.in/ojs/index.php/jrc/article/download/8/9

S. Edison

Papers

Survey of Cassava Mosaic Disease in Kerala

Sweetpotato in the Indian Sub-Continent

Rust of Queensland arrowroot (Canna edulis) caused by Puccinia thaliae: a new record for India

Meristem culture and thermotherapy in the management of sweet potato feathery mottle virus (SPFMV).

First report of Rhizoctonia solani causing blight on yam bean (Pachyrrhizus erosus) in India