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Spring regrowth is an important trait for perennial plants including alfalfa, the most cultivated forage legume worldwide. However, the genetic and genomic basis of the trait is largely unknown in alfalfa due to its complex genetic background of the tetroploid genome. The objective of this study was to identify quantitative trait loci (QTLs) associated with spring regrowth using high-resolution genetic linkage maps we constructed previously. In total, 36 significant additive effect QTLs for the trait were detected. Among them, 10 QTLs individually explained more than 10% of the phenotypic variation (PVE) with four in P1 and six in P2. Six overlapped QTLs intervals were detected with two and four intervals distributed in P1 and P2, respectively. In P1, both overlapped genomic regions were located on homolog 7D. In P2, the four QTLs with PVE>10% were co-localized on homolog 6D. Meanwhile, six pairs of significant epistatic QTLs were identified in P2. Screening of potential candidate genes associated with four overlapped QTLs (qCP2019-8, qLF2019-5, qLF2020-4, and qBLUP-3) narrowed down one candidate annotated as MAIL1. The Arabidopsishomolog gene has been reported to play an important role in plant growth. Therefore, the detected QTLs are valuable resources for genetic improvement of alfalfa spring vigor using marker-assisted selection (MAS), and further identification of the associated genes would provide insights into genetic control of spring regrowth in alfalfa.

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