Crop stress yields nutritional rewards

The debate over the merits of organic vs. traditional farming methods is a complex one, taking place both in the popular media and in the scientific literature. One particularly thorny issue has been the question of nutrition: strong arguments that organically-grown produce contains higher levels of desirable nutrients (such as vitamins and phenolic antioxidants) have been equally robustly attacked. Critics have pointed out that there is no evidence for a mechanism whereby nutrient production could be suppressed in the presence of fertilisers or pesticides used in traditional farming.

A study recently published in the open-access journal PLoS One, however, has challenged that view. The Brazillian researchers investigated two similar farms, one organic and the other traditional, and compared the size, weight, and nutritional profile of an otherwise identical crop of tomatoes. They found that the organically-grown tomatoes did indeed have higher concentrations of the nutrients in question than the traditionally-grown crop, and concentrations of Vitamin C were 55% higher in the organic crop at the time of commercial maturity – a truly significant difference.

But the study goes further, claiming that increased ‘oxidative stress’ during the devlopment of organically-grown tomatoes could be the mechanism responsible for the difference. Oxidative stress occurs when the plants are exposed to the radical ion superoxide, leading to increased production and activity of antioxidants as the plants try to convert superoxide to a less harmful molecule. This increase in antioxidant production during growth is then reflected in the nutrient concentration of the harvested fruit.

While this is indeed a novel and significant finding, a larger study based on more than one crop from a single farm each will be necessary to ensure the study is more widely applicable; at present the sample size is too small to confidently extrapolate the results to farming in general.

As a result of their findings, the researchers suggest that farmers should not attempt to eliminate plant stress entirely but rather accept some level of stress to be beneficial to their crop. Whether this will be applied in practice remains to be seen.