β-carotene and chlorophyll levels in cultivars and breeding lines of lettuce

The aims of this study were to determine the genetic variability to chlorophyll and β-carotene levels in lettuce, to check the correlation between these characteristics and to evaluate the potential use of a crisp head lettuce in breeding programs to increase β-carotene content in new cultivars. 18 lettuce cultivars (six crisp head, eigth butterhead and four leaf green) were used and eight advanced lines, derived from a cross between ‘Salinas 88’ (crisp head) and ‘Veronica’ (leaf green). The experiment was a randomized complete block design (RCB) with three replications and six plants per plot. At harvest time, samples were collected from leaves of each plant and evaluated to the chlorophyll content using the SPAD-502 and β-carotene content using high performance liquid chromatography (HPLC). There were significant differences for both characteristics. The breeding lines and crisp head cultivars, on average, displayed chlorophyll and β-carotene levels higher than other cultivars. The range of variation was from 110 to 528 units SPAD for chlorophyll and 1,343 to 3,638 μg 100 g-1 for β-carotene, highlighting the existence of genetic variability. The broad-sense heritability was higher than 0.80, with a correlation of about 0.82 for both characteristics. These results suggest the success possibility of indirect selection for high content of β-carotene using SPAD as reading for selection of plants with high chlorophyll content. Studies have demonstrated that the crisp head lettuce has much lower in β-carotene and chlorophyll than other lettuce types. This difference is probably due to the fact that the analyses have been done on internal leaves, which are used for consumption. The internal leaves develop protected by the external leaves resulting in photosynthesis decrease. In this paper we analyzed the outer leaves, which showed higher levels of chlorophyll and β-carotene. The crisp head cultivar ‘Salinas 88’ displayed a value of 2.658 μg 100 g-1 and line AFX007C-150-14, derived from this, 3,638 μg 100 g-1. These results highlight the potential use of crisp head lettuce ‘Salinas 88’ for obtaining new cultivars of other types with higher levels of β-carotene.