Mapping of quantitative trait loci for bolting time in bunching onion ( Allium fistulosum L.)

Late bolting is one of the most important agronomic traits in bunching onion (Allium fistulosum L.) because it affects the yield and quality of the harvested products during the spring and early summer. However, genetic and molecular studies of bolting time in bunching onion have not been reported thus far. To understand the genetic basis of bolting time in bunching onion plants, we evaluated the bolting time of two F2:3 populations derived from crosses between cultivars differing in bolting time and conducted quantitative trait loci (QTL) analysis based on the bunching onion genetic linkage map. When the KiC population derived from a cross between the ever-flowering line Ki and the late-bolting line C was grown under field conditions, two QTLs associated with bolting time were repeatedly detected on the linkage groups 1a on chromosome 1 (Chr. 1a) and 2a on chromosome 2 (Chr. 2a). However, the QTL on Chr. 1a was not detected when the KiC population was grown in a heated greenhouse under unvernalized conditions. A single QTL with major effect was identified exclusively on the linkage group Chr. 2a in the SaT03 population derived from a cross between early-bolting line Sa03 and late-bolting T03 evaluated under field conditions. QTL located on Chr. 2a in both populations were linked to the same marker loci, suggesting that these regions were strongly related. Simple sequence repeat loci linked to these QTLs had significant effects on bolting time in both populations.