Manipulation of bolting time for improved quality and greater sustainability in lettuce production

This project will take place at Warwick HRI in the University of Warwick (formerly the Horticultural Research International) and is aimed at understanding the molecular mechanisms controlling bolting in lettuce. Over 6,000 ha of lettuce, with a market value of over £80 million, was grown in the UK in 2005 (source DEFRA statistics, 2005). A major problem for lettuce growers is that the crop will sometimes initiate bolting (i.e. flowering) in the field before it is harvested. Whilst plants that are in the early stages of bolting are visibly indistinguishable from non-bolting plants, there are changes in the production of secondary metabolites in the leaves. These compounds may serve to protect the young floral buds from insect attack but give the lettuce plant a bitter and unpleasant taste and render the crop unsaleable. Delayed bolting, or greater holding ability in the field, is a desirable trait in commercial lettuce varieties as it preserves the quality of lettuces sold for consumption, and increases sustainability by reducing crop losses and wastage. This project will exploit the extensive knowledge on molecular mechanisms controlling flowering time gained from the study of model plants such as Arabidopsis. Lettuce genes that are homologous to genes known to control flowering in these model species will be identified. These will be good targets in which to induce variation in order to affect the control of bolting/flowering time. Inactivation of a gene that causes early bolting, for example, may cause later bolting which would mean that that lettuce variety will be less likely to bolt in the field before it is harvested. A greater understanding of the molecular mechanisms controlling flowering in crop species, and the natural variation that has evolved in crops to exert a robust effect on flowering, will also broaden our understanding of the flowering process. This project is a prime example of knowledge transfer from model to crop plants.

Premature bolting (flowering) of lettuce in the field before it is harvested is a major problem for growers as secondary metabolites are produced in the leaves which give the lettuce plant a bitter and unpleasant taste and render the crop unsaleable. Delayed bolting is a desirable trait in commercial lettuce varieties as it preserves the quality of lettuces sold for consumption, and increases sustainability by reducing wastage. This industrial partnership proposal will exploit the knowledge of molecular pathways controlling flowering time gained from model plants, and the large amount of genomic resources that have recently been developed for lettuce (eg. an extensive EST collection, an oligonucleotide tiling array of 35,000 unigenes, and a TILLING population), to identify genes controlling bolting time in lettuce, and either induce novel variation, or discover natural variation in these genes that can be used to delay bolting in lettuce. This will be done through four complementary approaches which vary in either the starting material or in the methodology used; a). screening EMS, or b). transposon mutagenised populations followed by identification of the site of the mutation using the tiling array, c).TILLING for mutations in lettuce homologues of known flowering time genes, d). screening a diversity set to identify natural variation affecting bolting time. The primary objectives of this research project are; i). The identification of lettuce genes controlling bolting time. These may either be homologues of known flowering time genes, or completely novel genes controlling bolting/flowering time. ii). The creation of late bolting lines in a modern iceberg lettuce cultivar which can readily be incorporated into breeding programmes to generate new varieties with greater holding ability. iii). The identification of naturally occurring alleles of known flowering time genes that have a robust effect on bolting time in different genetic backgrounds.