CROPS

Boosting cassava yields in Africa using molecular markers and tissue culture

Though native to South America, cassava (Manihot esculenta Crantz) is one of the most important food staples in sub-Saharan Africa. It is a very reliable source of dietary calories for smallholder farmers and their households because it can be cultivated relatively easily, without the need of costly inputs such as fertilizers. It is also gaining importance as a cash crop and offers immense potential for enhancing income and improving the livelihoods of these small-scale subsistence farmers.

However, to realize this potential, cassava crop yields in sub-Saharan Africa need to be boosted. For instance, the average yield of fresh roots per hectare is 10.2 tons in Africa, 12.5 tons in South America and 17.3 in Asia while worldwide it is 12.4.

Developing superior varieties of the crop in Africa benefits from increasing the genetic diversity of the breeding materials. There is a rich pool of cassava diversity, including its wild relatives in South America.

But the intercontinental transfer of cassava germplasm (living genetic resources), through seeds or stem cuttings, faces numerous constraints. For example, using seeds for this process has proven too difficult, time-consuming and expensive. The characteristics of the parents are difficult to reproduce in the offspring from seeds. Stem cuttings, on the other hand, pose a high-risk because their transport can spread pests and diseases across regions. Cassava germplasm from South America is also susceptible to a myriad of virulent pests and diseases found in Africa, in particular cassava mosaic disease (CMD).

To address these constraints, the National Root Crop Research Institute in Nigeria in 2004 pioneered the use of cell biology and molecular markers to introduce desirable traits of South American germplasm to cassava in Africa while at the same time increasing resistance to CMD.

Thousands of plantlets - miniature plants grown on sterile media in test tubes or flasks in the laboratory - were obtained from one of the world’s largest repositories of cassava germplasm, the International Center for Tropical Agriculture in Colombia. These aseptically grown plantlets have minimal risk of spreading diseases and pests and are thus not subject to the stringent quarantine conditions applied to the transport of other cassava germplasm. Through the use of molecular markers – analyzing and identifying fragments of cassava DNA linked to the traits of interest – scientists were able to rapidly combine into a new cassava variety the resistance to CMD obtained from a Nigerian variety and the high-yield, drought-tolerant traits contained in the South American types.

It is estimated that the improved cassava varieties, the fruit of these biotechnologies, could enhance the crop’s yield increases in Nigeria from the average 14 tonnes per hectare to 25 tonnes per hectare with an estimated additional revenue of 1.48 billion dollars for the cassava sector.

FORESTRY

Improving the quality of teak planting stock in Malaysia

Teak (Tectona grandis), a valuable tropical hardwood is widely planted in Asia, South and Central America and Africa but in many countries, the supply of teak planting stock cannot meet the demand. Teak has low seed yield per tree even in seed orchards as well as low and sporadic seed germination. This creates a problem for making teak germplasm available for smallholders and other tree planters, and for improving the quality of teak planting stock.

In Malaysia, the Sabah Foundation Group has been testing the mass propagation of high-quality teak clones using efficient nursery and micropropagation techniques since the early 1990s. This work has been carried out in collaboration with the Centre de Coopération Internationale en Recherche Agronomique pour le Developpement (CIRAD, France). Micropropagation – growing plant tissue cultures in laboratory conditions – is used to clone superior teak trees with desirable traits, such as fast growth, straight bole (trunk), minimal branching and high heartwood to sapwood ratio.

Successful application of these techniques from the laboratory to the ex-vitro acclimatization of plants to the field-ready stage has led to the increased availability of high-quality teak planting stock in Malaysia and worldwide exportation of teak plants to many tropical and sub-tropical countries. The technologies allow the mass production of clones from any outstanding teak tree regardless of its age.

The increased availability of high-quality teak planting stock has contributed to further development of intercropping systems based on teak and other cash crops such as rubbers, coffee, cocoa or even annuals such as legumes with nitrogen-fixing ability. These intercropping systems are of great interest to smallholders who are eager to not only maximize financial returns on their investments but also increasing the sustainability and diversity of their production systems.

LIVESTOCK

The global rinderpest eradication campaign

Global freedom from rinderpest (cattle plague) was declared in 2011 and marked only the second time in history that a disease has been eradicated worldwide, the first being smallpox. This achievement was the result of a combination of advances in the production of vaccines and strong cooperation among the international animal-health community, individual national veterinary services and local small-scale farming and pastoralist communities.

An infectious viral disease of cattle, buffalo, yak and numerous wildlife species, rinderpest caused devastating effects throughout history, including massive famines in regions where the disease spread unabated. Major waves of rinderpest outbreaks lasted for years and would result in mortality rates that could approach 90 percent in unprotected herds. This posed a massive risk to the food security and livelihoods of millions of large and small-scale farmers, including pastoralists. It is estimated that major outbreaks of rinderpest would destroy more than 70 million (or 14 million per year) of the 220 million cattle in Africa.

The first important step in the elimination of rinderpest was the development of a rinderpest virus capable of growing in cell culture and from it, the production of a quality-assured vaccine. Additional advances included technologies that allowed for this vaccine to be freeze-dried and stably stored for years.  However, the vaccine would lose its effectiveness when exposed to heat. Subsequently a vaccine more resistant to higher temperatures was developed, guaranteeing further effectiveness in remote areas.

An additional technological advancement was the development of diagnostic assays (tests) that could be carried out on the national herd of countries to establish, in a rapid and cost effective way, the vaccine coverage or to identify where the virus was circulating.

While samples of the virus that causes rinderpest are still stored in multiple laboratories in a few dozen countries, the disease no longer exists in nature. The last outbreak of rinderpest occurred in Meru National Park, Kenya, in 2001.

FISHERIES

Rapid detection of viral diseases in shrimp

Techniques that allow for the rapid detection of viral diseases have had a major impact on the cutting of losses in shrimp farming. The use of DNA-based diagnostic methods comes from the principle that each species of pathogen carries unique DNA or RNA sequences that differentiate it from other organisms thus offering high sensitivity and specificity for rapid screening for the presence of pathogen DNA.

Very small quantities of the viral DNA can be multiplied through the use of the polymerase chain reaction (PCR) – a tool to make more DNA - until there is a sufficient amount of the viral DNA to be detected in the laboratory. These methods have been adopted rapidly and used in diagnosis and for detection of many economically important viral pathogens of cultured finfish and penaeid shrimp. However, there are some limitations regarding their use, including "false negatives" caused by, for example, the selection of inappropriate host tissue sources, incorrect choice of DNA extraction methods, or low pathogen prevalence in the population being sampled – a situation that may erroneously affect the analysis and interpretation of test results.

The use of PCR has been introduced in India where shrimp aquaculture is mainly carried out by small- and medium-scale farmers located in remote villages - this included providing farmers with kits for collecting and preserving DNA. Since 2002, efforts to support shrimp farmers in disease control and coastal management have led to significant improvements in income and reduced shrimp disease risks.

An FAO–assisted project has supported local farmers form self-help groups or “clusters” to share experiences and implement better management practices. An economic analysis of 15 farmer groups in Andhra Pradesh showed that farmers adopting better management practices including using postlarvae (immature shrimp) for their shrimp stocks that had been screened in the laboratory for the presence of DNA from specific pathogens had higher profitability, lower production costs and were able to produce quality and traceable shrimp without using any banned chemicals.

The project has been highly successful in forming a self-help movement of farmers – from a mere five farmers who first adopted the cluster-farm approach in 2002, the programme swelled to more than 1 000 farmers in 30 aquaculture societies in five Indian coastal states by 2007.