Quantitative trait loci (QTLs) linked with root growth in lettuce (Lactuca sativa) seedlings

Abstract

In-field variation of transplanted lettuce (Lactuca sativa L.) due to variable soil and environmental conditions is one of the major restrictions in the optimization of production and yield. Marker-assisted breeding for lettuce varieties with a more rapid rooting phenotype has the potential to improve the performance of lettuce transplants. This study aimed to identify traits linked with increased primary root length, lateral root length and lateral root emergence in 14-day L. sativa seedlings from an intra-specific cross (Saladin × Iceberg). In total, 16 significant quantitative trait loci (QTLs) were associated with increased root growth traits that would allow direct introgression of the traits. Six of the QTLs were associated with increased primary root growth, accounting for 60.2% of the genetic variation for the trait. Three QTLs were associated with lateral root growth (38.6% of genetic variation); two QTLs were associated with lateral root length density (27.6% of genetic variation) and three with root number density (33.4% of genetic variation), and two QTLs were associated with mean lateral root length (21.1% of genetic variation). The statistical QTLs were located across 9 different linkage groups (LGs) representing loci on 7 of the 9 L. sativa chromosomes. A combination of restriction fragment length polymorphism (RFLPs) and Kompetitive allele specific PCR (KASPs) markers linked to these rooting traits were identified, which could allow breeders to select for a rapid establishment phenotype.