title: Genotype and environment effects on nitrate accumulation in a diversity set of lettuce accessions at commercial maturity: the influence of nitrate uptake and assimilation, osmotic interactions and shoot weight and development.
abstract: BACKGROUND
  The causes of the natural variation in nitrate accumulation and associated traits are studied using a diverse population of 48 mature lettuce accessions grown hydroponically in winter and summer seasons. Information on the effects of genotype, environment and their interactions will inform future selection strategies for the production of low-nitrate varieties more suited to meeting EU requirements for harvested produce.
  
  
  RESULTS
  The effects of genotype (G), environment (E) and G × E interactions were all significant, with nitrate concentrations lower but covering a wider range in summer. Concentrations of nitrate-N were positively correlated with those of water and total-N and negatively with assimilated-C in the shoot in both seasons, with all relationships partitioned according to morphotype and/or seasonal type. Corresponding relationships between nitrate-N and assimilated-N or with shoot fresh or dry weight were generally weak or inconsistent. Nitrate concentrations at an early growth stage were strongly related to those at maturity in winter, but not in summer when light levels were less variable.
  
  
  CONCLUSIONS
  The effects of genotype and environment on nitrate accumulation in lettuce are strongly influenced by morphotype, with most G × E interactions between accessions within the same morphotype predominantly of the non-crossover type. All low-nitrate-accumulating genotypes have increased concentrations of organic solutes (concentration regulation) and reduced water (volume regulation) to help stabilise osmotic potential within the shoots. Variability in nitrate accumulation arises more from differences in uptake than in efficiency of its chemical reduction. Genotypic differences in nitrate accumulation can be masked by changes in head morphology during maturation, provided that they are not confounded by substantial changes in intercepted light. Recent selection strategies do not appear to have produced lower-nitrate-accumulating cultivars.
authors.affiliation: Warwick Crop Centre, School of Life Sciences, Wellesbourne Campus, University of Warwick, Warwick CV35 9EF, UK. ian.burns@warwick.ac.uk
authors.forename: Ian G
authors.initials: IG
authors.lastname: Burns
authors.forename: Kefeng
authors.initials: K
authors.lastname: Zhang
authors.forename: Mary K
authors.initials: MK
authors.lastname: Turner
authors.forename: James
authors.initials: J
authors.lastname: Lynn
authors.forename: Sandy
authors.initials: S
authors.lastname: McClement
authors.forename: Paul
authors.initials: P
authors.lastname: Hand
authors.forename: David
authors.initials: D
authors.lastname: Pink
mesh_terms: D001692:Biological Transport; D057486:Carbon Cycle / Q000528:radiation effects; D003433:Crosses, Genetic; D005062:European Union; D005506:Food Contamination / Q000331:legislation & jurisprudence / Q000517:prevention & control; D059647:Gene-Environment Interaction; D014644:Genetic Variation; D005838:Genotype; D018527:Hydroponics; D018545:Lactuca / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects; D009566:Nitrates / Q000378:metabolism*; D058458:Nitrogen Cycle / Q000528:radiation effects; D009997:Osmotic Pressure; D018520:Plant Shoots / Q000254:growth & development* / Q000378:metabolism / Q000528:radiation effects; D015203:Reproducibility of Results; D012621:Seasons; D013472:Sunlight; D013997:Time Factors; D006113:United Kingdom; D014867:Water / Q000032:analysis
chemical_list: D009566:Nitrates; D014867:Water