S13 - Session P3 - Understanding the molecular and physiological basis of tipburn in lettuce

Authors: Andrew Beacham *, Katie Wilkins, Jim Monaghan, Julia Davies, Guy Barker

Background: Tipburn is a serious physiological disorder of lettuce ( Lactuca sativa ), causing leaf margin discolouration and collapse, leading to unsaleable crops and food waste. The condition is hard to predict and no completely effective control methods exist. Tipburn is poorly understood but appears to be associated with impaired calcium distribution. In Brassica oleracea ¸ vacuolar calcium transporters exhibit differential expression in tipburn-resistant and susceptible lines. We previously developed a commercially-relevant hydroponic assay to phenotype a Lactuca Diversity Fixed Foundation Set (DFFS) for tipburn resilience, identifying significant (p < 0.001) genotypic effects. Objectives: We will now use this assay to investigate the molecular basis of tipburn in lettuce. We hypothesise that expression of L. sativa homologues of Arabidopsis vacuolar calcium transporters may differ between tipburn-resistant and susceptible lettuce lines as in B. oleracea and that this could affect leaf calcium content and distribution. Materials and methods: We have identified putative homologues of Arabidopsis vacuolar calcium transporters in the L. sativa genome through reciprocal BLASTp analysis. We will determine their expression in the apex and base of tipburn-affected and symptomless leaves in selected DFFS and commercial lettuce lines by RT-qPCR. Calcium, magnesium and potassium levels in samples will be determined by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), in addition to calcium ion-selective electrode measurements and hyperspectral imaging. Fluo-8 dye will be used to collect preliminary in vitro leaf intracellular calcium concentrations. In addition, existing genotype by sequencing (GxS) data will be used to detect sequence differences in calcium-associated genes in the DFFS lines. Perspectives: Together, these data will begin to link molecular components to nutrient homeostasis in tipburn of lettuce. This project is funded by the UK BBSRC HortQFLNet initiative and carried out in association with Vertical Future and G's Fresh.