Farming News - Scientists recommend breeding wildness back into tomatoes

Scientists recommend breeding wildness back into tomatoes

10 Feb 2016
Frontdesk / Arable

Scientists have found that wild tomatoes are better able to protect themselves against the destructive whitefly than our modern, commercial varieties.

Lycopersicon pimpinellifolium, the wild tomato variety used in the scientists' experimentResearchers from Newcastle University have said that breeders, in their quest for larger, redder, longer-lasting tomatoes, have inadvertently bred out key characteristics that help the plant defend itself against predators.

In recent years, there have been calls to protect biodiversity, not only to improve the health and resilience of natural ecosystems, but also because ‘wild relatives’ of key crops on which humans rely can carry traits that will prove vital in combating new crop pests or diseases, improving the nutritional value of crops and helping adapt them to a changing climate.

According to the UN Food and Agriculture Organisation (FAO), over three quarters of the world’s agricultural biodiversity was lost over the course of the 20th Century, due to unprecedented changes in food and farming which saw farmers opting for higher-yielding or more predictable varieties to fit in with the needs of the supermarket model. It has been estimated that, in the US, over 80 percent of tomato varieties were lost over this period.  

This week, Newcastle researchers said wild tomatoes have a dual line of defence against glasshouse whitefly - the main insect pest for tomato growers, which feed on sap from leaves and can lead carry viruses and trigger fungal infections. These defences include an initial mechanism which discourages the whitefly from settling on the plant in the first place and a second line of defence which happens inside the plant where a chemical reaction causes the plant sap to "gum up" blocking the whitefly's feeding tube.

Thomas McDaniel, who described these mechanisms, said breeders need to rediscover some of the natural traits that have been lost over generations of plant breeding; speaking about the natural resistance of wild plant varieties Thomas said it that in many cases it would be better to "breed some of that wildness back in" to crop varieties instead of continuously looking for new methods of pest control.

"By selecting for certain characteristics we have inadvertently lost some really useful ones,” the biologist explained. "The tomatoes we buy in the supermarket may have a long shelf life and be twice as big as the wild varieties but the trade-off is an intensive and costly pest control regime -- both biological and in the form of chemical pesticides.

"Our research suggests that if we can breed the whitefly resistant genes back into our commercial varieties then we can produce a super tomato that not only has all the characteristics that we have selected for but is also naturally resistant to the whitefly."

McDaniel said current methods used to reduce whitefly impacts include biocontrol - parasitoid wasps which lay their eggs in the young whitefly which are then eaten by the hatching larvae (though this is a costly and labour intensive form of control), and chemical pesticides including controversial neonicotinoid preparations.

Commercial varieties more attractive to pests

In recent research funded by agri-science research council BBSRC, a team led by McDaniel found that when given free choice, whitefly were 80% more likely to settle and feed on the commercial tomato plants - in this case Solanum lycopersicum or 'Elegance' - over a wild variety - Lycopersicon pimpinellifolium.

By fitting gold wires to the back of individual whitefly and measuring the electro-chemical signals as they fed on the plant sap, the team found the insects spent more time 'roaming' and less time feeding on the wild varieties than those which settled on the commercial plants.

"One option would be to revert back to growing more of the older, wild varieties, and certainly we are already seeing a trend towards this, particularly on allotments and among smaller growers," McDaniel explained. "However, lower yields means the wild varieties are unlikely to be a viable option on a large scale.

"Our findings suggest that if we can breed the wild, whitefly resistant genes back into our tomatoes then it offers a real solution for the commercial tomato industry."