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

Abstract

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.

Striga

“…Thus, over 50 million ha of the arable farmland under cereals in subSaharan Africa are reported to be infested with Striga (Westwood et al, 2010). In West Africa, Striga has been estimated to infest 17.2 million ha, covering about 64% of the total area of the major millets like sorghum and pearl millet (Gressel et al, 2004), and the parasites have been reported to expand their infection range (Ejeta, 2007;Parker, 2012). Crop yield loss due to Striga infection has been estimated to range from about 10 to 31% in pearl millet experimental trial (Ramaiah, 1984).…”

“…Crop yield losses due to Striga attacks range from a few percent to complete crop failure and depend largely on the cereal host species and variety grown, rainfall distribution, soil fertility and the Striga seed density in soil Parker and Riches, 1993). The annual yield loss has been estimated to exceed US$10 billion (Gressel et al, 2004;Venne et al, 2009;Westwood et al, 2012;Pennisi, 2015). More recently, S. hermonthica has been identified as one of the seven most severe biological constraints to food production.…”

“…Millets thus play a critical role in ensuring food security in these regions Senthilvel et al, 2008 (Gurney et al, 2003(Gurney et al, , 2006Elzein and Kroschel, 2004;Vasey et al, 2005;Amusan et al, 2008). Indeed, Striga are the major and persistent biotic threat to production of these crops mostly grown on the hottest and driest marginal regions of sub-Saharan Africa, Middle East and large part of Asia (Gurney et al, 2002;Gressel et al, 2004;Ejeta, 2007;Rispail et al, 2007;Scholes and Press, 2008;Parker, 2012). At present, over 50 million ha of the arable farmland under cereals in sub-Saharan Africa are infested by Striga.…”

“…Benth. and S. asiatica (L.) Kuntze (henceforth denoted as Striga) are deemed to be the most economically important weeds parasitizing cereals (Berner et al, 1995;Cochrane and Press, 1997;Haussmann et al, 2000;Gressel et al, 2004;Gethi et al, 2005;Aly, 2007;Spallek et al, 2013). Striga infest millets, such as sorghum, pearl millet, finger millet, foxtail millet, little millet, proso millet, fonio, teff and barnyard millet (Chemisquy et al, 2010;Olivier, 1995;Parker, 2012;Atera et al, 2012), which represent the staple food and fodder crops of millions of poor rural families in the tropical and semi-arid regions of their cultivation, therefore are of utmost significance to subsistence farmers.…”

Integrated control of <em>Striga hermonthica</em> (Del.) Benth. in Burkina Faso through host plant resistance, biocontrol and fertilizers

“…S. hermonthica parasitizes all rain fed graminaceous crops in this region but is particularly problematic on sorghum, pearl millet and maize, the major staple cereals of over 300 million people in sub-Saharan Africa (Scholes and Press, 2008). Crop yield losses due to Striga parasitism have been estimated at 10.7 million tons per year in sub-Saharan Africa (Gressel et al, 2004). The methods most commonly used by farmers to control Striga in Burkina Faso are hand-pulling, crop rotation, and fallow, but these practices seldom lead to long-term reductions in the populations of S. hermonthica in infested fields (Traoré and Yonli, 2001).…”