Rather than trying to change the genome of the crop, which has been the more usual approach to GM, a manipulated genome of the maize streak virus (MSV) is inserted into the plant, in an approach that bears some resemblance to vaccination.

Dionne Shepherd, who led the team which developed the mutated gene, explained that MSV-resistant maize is the first genetically engineered crop developed and tested solely by Africans.

"South Africa is already the sixth-largest grower of GM crops in the world, but the perception of GM in the rest of Africa is poor - it`s currently banned," Dr Shepherd told BBC World Service`s Science In Action programme.

"But I think it`s more the multi-nationals that the rest of Africa is scared of. We`re hoping that our MSV-resistant maize, developed by Africans for Africa, will help change this negative perception."

Mutated protein

The maize streak virus can devastate most of a maize crop if it takes hold.

The virus stunts the growth of the maize and leads to abnormal crop development. Sometimes there is no yield at all.

Endemic to Africa, the virus gets its name from the yellow-white streaks it leaves across the leaves of the plants.

To tackle the virus, the scientists used what is called pathogen-derived resistance - using a gene from the virus itself to protect the plant.

"In our case, we used the gene that the pathogen requires to replicate itself, and we mutated it to make it non-functional.

"Then we inserted it into the plant genome. What then happens, the plant produces large amounts of this mutated replication protein, and when the virus enters the plant cell the mutated protein will recognise the virus`s native replication protein and bind to it.

"By binding to it, it interferes with the virus`s replication."

Before field trials go ahead, however, the scientists have to perform a risk assessment on the plant - by checking such aspects as whether the foreign protein is digestible, that it is not an allergen, and that it will not have a negative impact on other organisms or the environment.

These checks will "all take quite some time," Dr Shepherd said, meaning field trials may be another year off.

With additional monitoring required over a number of growing seasons, it is estimated it will be around five years before the plant is a commercial product.

Dr Shepherd admitted, however, that the "main issue" will be the cost of the crop, and whether it will be out of the price range of the poor farmers who need it the most.

Their commercial partner is South African seed company Pannar - but Pannar is not large enough to be able to afford the rigorous testing of the product.

"They are definitely committed to making the seed affordable for small-scale or poor farmers, but to do that they will probably need some help, maybe from the government, to help fund the risk assessment,"

© BBC MMVII