London (19.03.17) – One of benefits seen to be arising from the use of GM-crops in agriculture is an increase in yield: the cultivation of GM-crops often produces more output for a given input of materials and labour than do the corresponding non-GM varieties (1). That claim, however, has often been challenged by opponents of the technology on the grounds that there has been no increase in the actual underlying yield of any of the commercial plants so far modified genetically (2). Who is right and what does this conflict in views mean?

The disagreement in part derives from different ways in which the concept of “yield” is interpreted. If, by using a different procedure or different plant strains, growers secure more output from the same input, their yields will have improved. This does not necessarily mean that each and every plant is more productive since all agricultural production is subject to losses along the way: not all seeds sown will germinate, not all plants will be equally healthy, crops suffer from attacks by insects, worms and other animals, from fungi, bacteria and viruses. There are also disadvantage arising from weed infestation: crowding out of the crops plants and perhaps partly shielding them from access to sunlight which will reduce their growth and fruition.

The quantities of potential food products lost are enormous. Some people takes the view that some 40% of food crops planted worldwide never reach consumers’ plates. The FAO in a recent publication (3) estimates that “each year, the world loses or squanders a third of the food it produces. This means that somewhere between planting seeds in fields and providing nourishment to the world’s 7 billion people, approximately 1.3 billion tonnes of food with a value of more than US$1 trillion is lost or wasted. These numbers are simply untenable in a world where, according to FAO, some 870 million people do not have enough to eat.” Quite so.

Of course, traditional breeding methods of improving yields have in some cases been highly successful. Thus, a report from India just a few days ago described a cotton variety which needs only 100 days to mature (compared with the more usual 170-240 days) and with a higher yield of cotton at harvest (4).

Hitherto, agricultural biotechnology (genetic modification) has allowed growers to control a number of specific problems reducing yield: insect attack on maize and cotton; virus disease of papayas, weed infestation in the cultivation of maize, soya. oilseed rape (canola) and sugar beet; all are in use commercially in various countries. Just recently, maize has been engineered to deliver strands of so-called interfering RNA that silence toxin-producing genes in a fungus which commonly grows on the crop. Thus, the plants themselves stop Aspergillus growing on the cobs to prevent it producing the aflatoxin that causes liver disease and cancer in people consuming infected maize (5). This is a valuable development but it does have a limitation: it may be effective only while the plant is actually growing and may not prevent toxin production during storage. Post-harvest deterioration and losses of food during storage and transport to market can be serious factors in reducing the quantities of wholesome food reaching consumers.

From a GM-perspective, perhaps the most interesting recent finding came from a team in Belgium, a country whose population (or, at least, whose government) are not wildly enthusiastic about GM-technology (6). They found that “that modulating the expression of the maize PLASTOCHRON1 (ZmPLA1) gene, encoding a cytochrome P450 (CYP78A1), results in increased organ growth, seedling vigour, stover biomass and seed yield. The engineered trait is robust as it improves yield in an inbred as well as in a panel of hybrids, at several locations and over multiple seasons in the field”.

This, it seems, is an unequivocal case of genetic modification increasing the intrinsic yield of a plant product.

Sources:

1. Do GM crops increase yield? Monsanto (26.11.12) (http://www.monsanto.com/newsviews/pages/do-gm-crops-increase-yield.aspx)

2. Truth: GM crops do not increase yield potential – and in some cases decrease it. GMO. Myths and Truths (2015) (http://earthopensource.org/gmomythsandtruths/sample-page/5-gm-crops-impacts-farm-environment/210-2/)

3. Seeking end to loss and waste of food along production chain. Food and Agriculture Organization of the United Nations (2017) (http://www.fao.org/in-action/seeking-end-to-loss-and-waste-of-food-along-production-chain/en/)

4. Vivek Deshpande (15.03.17). Cotton variety which needs only 100 days to mature developed. Indian Express (http://indianexpress.com/article/india/cotton-variety-which-needs-only-100-days-to-mature-developed-4569502/)

5. Dhiraj Thakare, Jianwei Zhang, Rod A. Wing, Peter J. Cotty and Monica A. Schmidt (10.03.17). Aflatoxin-free transgenic maize using host-induced gene silencing. Science Advances (http://advances.sciencemag.org/content/3/3/e1602382#aff-1)

6. Xiaohuan Sun and 18 collaborators (16.03.17). Altered expression of maize PLASTOCHRON1 enhances biomass and seed yield by extending cell division duration. Nature Communications, 8, Article number 14752 (http://www.nature.com/articles/ncomms14752#auth-1)

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