Growing more aware of tomatoes' weaknesses.
THE drive to breed bigger and better tomatoes has made them a soft touch for pests, research on Tyneside has shown. Led by Newcastle University, the research indicates that wild tomatoes are better able to protect themselves against destructive whitefly than modern, commercial varieties.
The study shows that the quest for larger, redder, longer-lasting tomatoes has led to the loss of key characteristics which help the plant defend itself against attack.
Wild tomatoes have a double defence against whitefly, with an initial mechanism discouraging the insect from settling on the plant in the first place.
A second line of defence inside the plant involves a chemical reaction, causing the plant sap to 'gum up' and block the whitefly's feeding tube.
Thomas McDaniel, the PhD student who led the research at the university's school of biology, says the findings highlight the natural resistance of wild plant varieties and suggests the need to "breed some of that wildness back in" instead of continuously looking for new methods of pest control.
"By selecting for certain characteristics we have inadvertently lost some really useful ones," said Thomas.
"The tomatoes we buy 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 supertomato that not only has all the characteristics that we have selected for but is also naturally resistant to the whitefly."
The glasshouse whitefly is the most troublesome pest for the UK's tomato growers.
It damages the plant in three ways - by extracting sap and therefore nutrients, by creating a sticky honeydew on the surface of the plant which attracts mould, and by transmitting damaging plant viruses through its saliva.
Currently, 'bio-control' methods, such as the parasitoid wasp, are used to reduce the impact of the whitefly on tomato crops.
The wasp lays its eggs in the young whitefly, which are then eaten by the hatching larvae.
However, for control to be effective, the wasps need to be released on a weekly basis, which is costly and labour intensive.
As a result, most growers also use chemicals, including the controversial neonicotinoid pesticides, which have been linked to dwindling bee populations. In the study, funded by the Biotechnology and Biological Sciences Research Council, it was found that when given free choice, the whitefly were 80% more likely to settle and feed on the commercial tomato 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," said Thomas. Seed catalogues for gardeners now offer so-called "heritage" tomato varieties. "However, lower yields means the wild varieties are unlikely to be a viable option on a large scale," said Thomas.
"Our findings suggest that if we can breed the wild, whitefly-resistant genes back into tomatoes - either through a selective breeding programme or genetic engineering - then it offers a real solution for the commercial tomato industry."
Project supervisor Dr Barry Brogan, also from Newcastle University, said the findings also highlighted the importance of maintaining biodiversity. "There has been growing interest in traditional and wild varieties of fruit and vegetables, driven mainly by people wanting to recapture the tastes of their childhood," he said.
"But actually it's playing a vital role in protecting these older varieties and maintaining biodiversity. "If we allow our wild species to be lost then we risk losing potentially useful traits that we might need at a later date."
PhD student Thomas McDaniel's research has shown that wild tomatoes have greater resistance to whitefly than those grown for shop shelves