Food security challenges in Sub-Saharan Africa: The potential contribution of postharvest skills, science and technology in closing the gap

More than half of global population growth between 2013 and 2050 is expected to occur in Africa and is projected to more than double from 1.1 billion to 2.4 billion people by 2050. Estimates suggest that globally, sustainable food production will need to increase by 70%. It is essential that postharvest loss (PHL) reduction occurs alongside this increase in sustainable food production and access to meet the enormous food demand. The paper examines the grain PHL levels in Sub-Saharan Africa (SSA) and their implications. The PHL reduction strategies, their merits and limitations are analysed in terms of appropriateness to smallholder farmers, who form the majority of the farming community in Africa. The paper further identifies emerging postharvest research and development issues and the implications at various levels. The need to consolidate the understanding, approaches and metrics of PHL is highlighted. This will enable losses to be measured more quickly, objectively and comparably across commodities and geographical locations in Africa and beyond, and to assist in decision-making and measuring the impact of different initiatives. That PHL reduction is now an aspiration of many high-level development plans across SSA is a significant step forward. However, the challenge still remains of converting this attention into meaningful practical actions and increased knowledge and skills at the scale required to enhance food security across the region

Field assessment of the efficacy and persistence of diatomaceous earths in protecting stored grain on small-scale farms in Zimbabwe

Farmers and grain traders in sub-Saharan Africa are forced to sell stored produce prematurely because of deterioration due mostly to insect damage. Producers expressed a need for a relatively cheap and safe method of insect control. Diatomaceous earths (DE) offer safer alternatives to synthetic chemicals, but information on their efficacy under tropical small-scale farming conditions is lacking. Two commercially available DE products, Protect-Its and Dryacides, were tested against the major post-harvest insect pests of grains and pulses. On-farm field trials in Zimbabwe showed that both inert dusts gave significant protection against insect damage when admixed with farm stored maize, sorghum and cowpeas for periods of 40 weeks. However, efficacy of these DEs is closely linked to the application rates and differs between commodities, locations and insect pests. An admixture application rate of 0.1% w/w of Protect-Its or Dryacides can be recommended to protect both maize and cowpea grain that is to be stored for 4 months or longer in Zimbabwe. However, Dryacides was not effective in preventing damage to sorghum grain by the bostrichid Rhyzopertha dominica unless applied at a higher rate of 0.2% w/w

Small-scale farmer perceptions of diatomaceous earth products as potential stored grain protectants in Zimbabwe

Farmers repeated prioritisation of the need for improved methods of controlling insect damage to stored commodities in Zimbabwe led to the search for alternative grain protectants to the locally available organophosphate-based pesticides. In field trials the diatomaceous earth (DE) products, Protect-Its and Dryacides, gave good protection to threshed maize, sorghum and cowpea from insect attack during 8 months storage, enabling households to increase both their food security and control over grain sales. However the initial trials, although on-farm, were researcher-managed and only evaluated by farmers at the end of the storage period. No information existed on how effective DEs were under real farmer management. At the start of the 1999/2000 storage season, farmers in Buhera and Binga districts set up trials in their own granaries using their own maize and sorghum grain, respectively. During a 7 months storage period they evaluated the application of 0.1% w/w Protect-Its compared to their typical grain protection methods. At 5 and 7 months storage, farmers compared the treatments using the parameters they view as important such as insect damage, expected ‘sadza’ yield and quality and sale price. The DE treatments outscored other practices for all parameters and farmers were keen to purchase DEs to protect their future harvests. Grain samples from the same trial were also analysed in the laboratory at 5 and 7 months for insect populations, damage and moisture content. Although grain damage and insect numbers were higher in the typical grain protection treatment than the DE treatment, the differences were not statistically significant

Maize seed selection by East African smallholder farmers and resistance to Maize streak virus

Interviews identified that most small-scale maize farmers in central Uganda and in the Southern Highlands of Tanzania plant home-saved seed of landraces or seed derived from various open-pollinated and hybrid varieties. Some farmers also bought a portion of their seed, either certified seed, locally traded seed or even maize sold for consumption. Selection for home-saved seed was generally among harvested cobs. Big cobs with many, regularly arranged, large, white, flint kernels were preferred. A maize cob may bear several hundred seeds, so a farmer needs to save <1% of cobs for seed. A form of resistance in which plants show only moderate symptoms and suffer only a small reduction in yield when infected has been incorporated in some released varieties. Because not all plants in most crops are infected and because plants uninfected with Maize streak virus (MSV) tend to produce bigger cobs than infected resistant plants, the few cobs selected by a farmer for seed may all be from the uninfected ‘escapes’, with no preferential selection of resistant types. On-station simulation of the farmers’ selection process in a crop of the MSV-resistant maize variety, Longe 1, confirmed this. An alternative very strong form of MSV resistance was identified

Sweetpotato infestation by Cylas spp. in East Africa: II. Investigating the role of root characteristics

The response of the sweetpotato weevil Cylas puncticollis (Coleoptera: Brentidae) to roots of different sweetpotato cvs was investigated as part of a project to examine the factors that affect susceptibility of sweetpotato cvs to weevil infestation in the field. Laboratory experiments were conducted at two sites (Ukiriguru and Kibaha) in Tanzania and at one site (Serere) in Uganda to determine if the harvested storage roots of sweetpotato cvs differed in their acceptability to C. puncticollis or if any root antibiosis towards C. puncticollis existed. For all experiments cultivar effects for the total number of emerging adults were significant to at least 10% and in most cases were much more significant. At Ukiriguru and Kibaha, the results showed reasonable consistency between years, and of the four cultivars used at both sites, fewer C. puncticollis adults emerged from roots of Sinia and Budagala than from SPN/0 and Mwanamonde on all occasions. A relationship between laboratory experiments and crown damage by Cylas spp. in the field suggests that cultivar differences in attraction/deterrence for Cylas spp. exist. However, correlations between adult emergence in laboratory antibiosis experiments and field infestation levels were generally not strong. Although this indicates that cultivar selection by laboratory experiments is not a useful strategy for reducing field infestation, there may be potential for using such techniques to select cultivars that are resistant to attack during longterm storage

Do diatomaceous earths have potential as grain protectants for small-holder farmers in sub-Saharan Africa? The case of Tanzania

Participatory on-farm field trials were set up over three storage seasons, from 2002 to 2005, in different agroecological zones of Tanzania to compare the efficacy of the enhanced diatomaceous earths (DEs) Protect-Its and Dryacides alone or combined with the pyrethroid permethrin. Other treatments included three commercially available synthetic chemical dilute dusts, containing 1.6% pirimiphos-methyl and 0.3% permethrin (Actellic Super and Stocal Super from different manufacturers) and 1% fenitrothion and 0.13% deltamethrin (Shumba Super); traditional protectants; and a locally available DE collected from Kagera in north-west Tanzania. Treatments were applied to maize and sorghum grain and dried beans. Insect pests are the main threat during storage, which in Tanzania includes the devastating larger grain borer, Prostephanus truncatus. All the grain protectants, except the traditional ones, kept damage incidence well below that of the untreated controls, and usually below 10% for periods of 40 weeks of storage. Exceptions occurred when grain was badly infested prior to treatment, in which case Actellic Super dust was more effective than the DEs. Very little difference in damage was observed between the DE treatments until 40 weeks of storage. In addition to the commercially available synthetic grain protectants, Protect-Its 0.25% w/w or Protect-Its 0.1% w/w plus permethrin at 2 mg/kg can be recommended to protect dry un-infested, winnowed maize and sorghum grain that is to be stored on-farm in sacks or woven granary baskets for periods of 4 months or more in Tanzania. Beans can be protected with lower application rates of Protect-Its 0.05% w/w or Dryacides 0.1% w/w. The study also demonstrated that Actellic Super dust obtained from an approved source and applied according to the manufacturer’s recommendations is effective in protecting stored maize, sorghum and beans for periods of at least 40 weeks—contrary to many of the suggestions that this product is no longer effective in Tanzania

Sweetpotato infestation by Cylas spp. in East Africa: I. Cultivar differences in field infestation and the role of plant factors

Sweetpotato weevils (Cylas spp.) constitute a major constraint upon sweetpotato production and utilization world-wide. Attempts to breed for resistance to Cylas spp. have had limited success. However, there are reports of variation in the susceptibility to weevil attack in the field among cultivars in East Africa. Field trials were conducted at two sites (Ukiriguru and Kibaha) in Tanzania and at one site (Serere) in Uganda to determine the extent to which sweetpotato cultivars presently available in East Africa consistently differ in their susceptibility to field infestation by Cylas spp. and to identify the plant factors that determine the levels of susceptibility. Several methods to assess levels of field infestation were tested, and their relative merits are discussed. Significant cultivar differences in susceptibility to Cylas spp. infestation were observed for four out of six trials carried out over 2 years. The exceptions were cases where infestation levels were either very low or very high. Linear regression models of infestation suggest that the following plant characteristics are associated with low susceptibility to Cylas spp. infestation: increased distance of roots from the soil surface, fewer soil cracks, fewer exposed roots and a high foliage yield. Both the distance of the roots from the soil surface (shortest weevil distance) and foliage yield differ significantly between cultivars. The former cannot be approximated by measurement of root neck length, but must be measured in situ