One bioengineered maize variety incorporating resistance to multiple pests and pathogens would have the potential to drastically improve production of the staple crop in sub-Saharan Africa, according to a team of researchers.
In a paper in the journal Pest Management Science, a team led by Jonathan Gressel argued that with maize yields stagnating and conventional breeding limited in its ability to counter the multiple weed, pathogen and insect threats of the continent, a high-tech solution is needed.
“Our analysis clearly shows that traditional breeding cannot pyramid enough needed genes to deal with the pest constraints facing sub-Saharan maize for two reasons: first, maize does not have all the necessary requisite genes in its genome; and second, where it does, the traits needed are polygenic and combining such traits is a formidable task,” they explained.
They suggested that breaking the current impasses would require multiple resistance traits, genetically engineered into a locally adapted, high yielding elite maize variety — and that this future is in sight. They compiled a list of resistance genes to such threats as mycotoxins and fall armyworm that could be ‘stacked’ at one location in the crop’s chromosome, many of which are already commercially used in the Americas.
Some of the same gene constructs could also be applied to sorghum and millet, which are significant crops for African farmers. They face similar problems with multiple biological threats in the field and limited scope for addressing them using traditional breeding.
While the background in available genetic material is hugely advantageous, another factor encouraging such a move is that the taboo against genetically engineered crops in Africa has waned in recent years. Bt cotton is now grown in several countries, while Nigeria and Ghana have approved genetically-engineering cowpea which is resistant to insect pests.
“Multi-trait biolistic transformation with known transgenes into a locus in a single maize strain coupled with conventional breeding of this single transgene locus complex into locally adapted inbreds and open-pollinated varieties has the potential to increase maize yields above and beyond present and future needs,” they wrote.
This would make exporting excess production possible, but with long-distance transport costs high and the possible risk of prices crashing locally due to oversupply, farmers would be able to simply plant less maize to meet their requirements. This would allow them to rotate unused land to legumes, cash crops, forage or agroforestry, and so bring in integrated pest management principles which could delay resistance to the components of the genetically engineered crop.
“The proposed transgenes are not a forever solution,” they warned. “Additional transgenes are needed to deal with new problems as they arise, whether that be evolved resistance or changed pest spectra.”
This is a problem for the future, however. The most pressing issue now is exactly how to engineer resistance traits into maize, they conceded. Transformation using Agrobacterium is proven, but only allows for the introduction of a limited number of genes, while CRISPR–Cas9 gene editing offers a tantalising cutting edge option, albeit nobody has successfully achieved what are known as ‘knock-ins’ using the technology in maize to date.
“Undoubtedly, site targeted multigene insertion will be achieved in the future, but this will take some time,” they added.
