11. Reducing Demand: Drought Resistant Crops

My last post looked at increasing the proportion of water (diverted from a storage reservoir) that ends up available in the plant root zone. This post looks at increasing how efficiently plants use this available water.

Naturally efficient water users:

Some plants are inherently more efficient water users than others. The term ‘xerophyte’ is given to plants that are particularly efficient. Unfortunately we don’t tend to eat xerophytes because they are often poisonous or spiky and we have a cultural aversion to them. Some people do eat them (e.g. the prickly pear cactus is commonly eaten in Mexico) and the FAO believes that this consumption should increase. However, cacti are not calorie dense and we are unlikely to convince the entire African population to start eating them overnight! Therefore we need to find ways to make current staple crops more water efficient. Maize is the most widely grown crop in Africa and is the main food source for over 300 million Africans (La Rovere et al., 2014). As a cereal crop it already has a relatively low water requirement, see table below (Mekonnen & Hoekstra, 2010)... but could we make this lower still?

Fig. 1 Prickly pear cactus growing in Mexico

Fig. 2 The water footprint of some selected crop products (Source: www.waterfootprint.org,  based on data from Mekonnen & Hoekstra, 2010).

Selective breeding:

In 2006, the Drought Tolerant Maize for Africa (DTMA) initiative was set up by CIMMYT and IITA and funded by the Bill & Melinda Gates Foundation. The project aimed to selectively breed maize varieties that are 30% more productive (than current varieties) when grown under 'moderate drought conditions'. So far the project has released over 160 new drought tolerant varieties in 13 African countries. However, realization of the predicted benefits has received limited empirical study (Fisher et al., 2015).  Furthermore, inadequate information, high seed price and lack of seed availability remain significant barriers to wide-scale adoption.

Fig. 3 A rural farmer from Ethiopia holds up the cob of a drought resistant variety of maize developed by the Drought Tolerant Maize for Africa (DTMA) initiative (Source: Annual Maize Report, 2013) 

Genetic engineering (GE):

Selective breeding can be slow and limited in scope (e.g. some plants can’t be cross-bred/some traits can’t be conferred via breeding). GE can overcome these issues. In 2013, Monsanto launched the Water Efficient Maize for Africa (WEMA) project in collaboration with AATF. They used GE methods to develop more water efficient maize hybrids (branded as ‘DroughtTEGO) to sell to smallholder farmers in SSA. They claim that farmers using these hybrids have achieved 20-35% greater yields under moderate drought conditions. However, GE crops continue to generate strong opposition, largely because people believe they are bad for our health, despite numerous peer reviewed studies demonstrating their safety. Furthermore, the barriers to adoption discussed above also apply to most GE crops. 

Fig. 4 A slightly humorous photo portraying anti-GE attitudes (GMO stands for 'Genetically Modified Organism' and is generally used to refer to Genetically ENGINEERED organisms, even though selective breeding is technically a form of genetic modification)

Microbial inoculation:
Recent research suggests that we can increase water use efficiency without changing plant genetics! Studies have found that drought tolerance can be conveyed by transferring microbial colonies from the roots of tolerant plants to the roots of less tolerant plants (East, 2013)! For example, inoculating rice with fungus from salt-tolerant dune grass reduced its water needs by 50%, whilst increasing its yield. In fact, a company called ‘Adaptive Symbiotic Technologies’ (est. 2008) now produces ‘microbial inoculants’, which can be applied to crop plants to increase their water efficiency. However, these are not yet available in SSA!

Fig. 5 Scanning electron microscope images of soil microorganisms. Some of these microorganisms can be used to convey drought tolerance from more tolerant to less tolerant plant species (Source: Dennis Kunkel)

Clearly more drought resistant crops do exist but significant barriers to adoption remain. These are similar to those for efficient irrigation technologies, namely high cost, lack of availability and lack of education.