QTLs for shelf life in lettuce co-locate with those for leaf biophysical properties but not with those for leaf developmental traits

Abstract

Developmental and biophysical leaf characteristics that influence post-harvest shelf life in lettuce, an important leafy crop, have been examined. The traits were studied using 60 informative F9 recombinant inbed lines (RILs) derived from a cross between cultivated lettuce (Lactuca sativa cv. Salinas) and wild lettuce (L. serriola acc. UC96US23). Quantitative trait loci (QTLs) for shelf life co-located most closely with those for leaf biophysical properties such as plasticity, elasticity, and breakstrength, suggesting that these are appropriate targets for molecular breeding for improved shelf life. Significant correlations were found between shelf life and leaf size, leaf weight, leaf chlorophyll content, leaf stomatal index, and epidermal cell number per leaf, indicating that these pre-harvest leaf development traits confer post-harvest properties. By studying the population in two contrasting environments in northern and southern Europe, the genotype by environment interaction effects of the QTLs relevant to leaf development and shelf life were assessed. In total, 107 QTLs, distributed on all nine linkage groups, were detected from the 29 traits. Only five QTLs were common in both environments. Several areas where many QTLs co-located (hotspots) on the genome were identified, with relatively little overlap between developmental hotspots and those relating to shelf life. However, QTLs for leaf biophysical properties (breakstrength, plasticity, and elasticity) and cell area correlated well with shelf life, confirming that the ideal ideotype lettuce should have small cells with strong cell walls. The identification of QTLs for leaf development, strength, and longevity will lead to a better understanding of processability at a genetic and cellular level, and allow the improvement of salad leaf quality through marker-assisted breeding.

QTL analysis reveals the genetic architecture of domestication traits in Crisphead lettuce

“…It has already been shown that RILs of the cross between cultivated L. sativa and wild L. serriola used in this study have differentiated root architecture (Johnson et al 2000), seed and seedling traits (Argyris et al 2005), and leaf biophysical and developmental traits (Zhang et al 2007). To our knowledge no classical or quantitative genetic data are available on the genetic basis of traits that differ between wild and cultivated lettuce: the available studies have mostly focussed on offspring fertility of different Lactuca species and among cultivars crosses (Thompson et al 1941;Lindqvist 1960a, b;Prince et al 1979;de Vries 1990).…”

“…maps, it appears that regions overlap with those found by Zhang et al (2007) for leaf biophysical and developmental traits, such as leaf area (LG3) and absolute growth rate (LG7) although the exact map alignment is difficult due to limited marker overlap. Such clustering is consistent with either many linked genes and/or of few genes with major pleiotropic effects.…”

“…capitata L. nidus jäggeri Helm) and its wild relative L. serriola f. serriola (UC96US23). The RILs are from the same set as used in Argyris et al (2005), Johnson et al (2000), and Zhang et al (2007). In total, 114 RILs were grown in the greenhouse under 6 h dark and 18 h light, a minimum of 18°C, under 600W SON T-Agro lamps generating on average 160 lmol/m 2 / sec at plant level.…”

Oxidative discolouration in whole-head and cut lettuce: biochemical and environmental influences on a complex phenotype and potential breeding strategies to improve shelf-life

“…Zhang et al (2007) identified strong negative correlations between discolouration and the plasticity and elasticity of leaf tissue, and a positive correlation with break strength, suggesting that subsequent discolouration may be related the ability of the lettuce tissue to deform in response to physical pressure. Not only may wound sites discolour, either during crop production or in storage, but the increased phenolic levels and enzyme activities produced in response to wounding may represent increased discolouration potential if apparently healthy material, damaged shortly before or during harvest, is later cut for prepared salad production.…”

“…Although Wurr et al (2003) found no relationship between tissue strength or stiffness and discolouration, physical leaf properties such as break-strength, plasticity, elasticity and cell area have been correlated with shelf-life in a cross between L. sativa and L. serriola, suggesting lettuce types with small cells and strong cell walls have better shelf-life (Zhang et al 2007). This observation supports the suggestion that cellular integrity may be important in reducing discolouration and Wagstaff et al (2010) noted that shelf-life increased by up to 66% with a concomitant reduction in membrane permeability in transgenic lettuce plants expressing reduced levels of the enzyme xyloglucan endotransglucosylase/hydrolase, which is involved in regulating cell wall rigidity.…”