Clarifying the immune system of tomato plants offers opportunities for horticulture
30 November 2011
Cultivated tomatoes lack certain sugar compounds that wild tomatoes do have. Wild tomatoes use these compounds to protect themselves from being consumed by insects. This was discovered during systems biology research performed by Dr Kirsten Leiss and PhD student Mohammad Mirnezhad. Plant breeders can use this knowledge to introduce characteristics of wild tomatoes back into cultivated tomatoes. That could mean that insecticides are no longer needed in the future. Mirnezhad defended his doctoral thesis on 30 November.
Wild tomatoes originate from the Andes region of South America. They are small, green have an unattractive shape and taste bitter. To please consumers, plant breeders have turned them onto large red fruits with a pleasant taste. However as a result of this the tomato lost its natural immune system to insects and pathogens. The researchers used metabolomics to discover how the immune system of tomatoes works. This technique is used to follow traces of metabolic products such as amino acids and glucose cells in tissues and organs. However, the technique had not previously been used for research into insect resistance in plants.
Sugar replaces insecticides
Leiss ordered wild tomato seeds from a breeding institute in California and cultured these together with plants from Dutch varieties. The aim was to test the tomato plants for their sensitivity for herbivorous insects and the presence of antibodies against these natural enemies. Leiss and Mirnezhad found acyl sugars in wild tomatoes; sugar compounds that render the plant resistant to insects such as thrips and white fly. These insects suck plant cells empty and can transmit viruses. Cultivated tomatoes lack these acyl sugars. To gain a complete picture of the immune system of plants, PhD student Mirnezhad investigated the thrips that pose a threat to tomato plants. After all, insect pests can just as easily become resistant to the natural defences of plants as they can towards insecticides.Mirnezhad discovered that thrips on lettuce, leek and chrysanthemums are genetically different even though they belong to the same species. This genetic variation was not associated with differences in food preference. The thrips just as eagerly consumed all of the plants tested but they did have a clear preference for the plant they wished to pair on. How this behavioural difference can be explained by the plant’s chemistry is a following step in the research.
Leiss and Mirnezhad carried out their research at Leiden University with funding from NWO and NGI (Netherlands Genomics Initiative). Thanks to this fundamental research the discovery of Leiss and Mirnezhad can be translated into a practical solution with funding from Technology Foundation STW. With this grant Leiss hopes to develop a ‘metabolomics resistance test’. Plant breeders could use such a test to predict the resistance of new vegetables and ornamental flowers to insects and pathogens. This research could therefore ultimately contribute to the sustainability aspect of the Top sectors Horticulture and Agrofood.
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