Abstract
Pears with red skin are attractive to consumers and provide additional health benefits. Identification of the gene(s) responsible for skin coloration can benefit cultivar selection and breeding. The use of QTL-seq, a bulked segregant analysis method, can be problematic when heterozygous parents are involved. The present study modified the QTL-seq method by introducing a |Δ(SNP-index)| parameter to improve the accuracy of mapping the red skin trait in a group of highly heterozygous Asian pears. The analyses were based on mixed DNA pools composed of 28 red-skinned and 27 green-skinned pear lines derived from a cross between the ‘Mantianhong’ and ‘Hongxiangsu’ red-skinned cultivars. The ‘Dangshansuli’ cultivar genome was used as reference for sequence alignment. An average single-nucleotide polymorphism (SNP) index was calculated using a sliding window approach (200-kb windows, 20-kb increments). Nine scaffolds within the candidate QTL interval were in the fifth linkage group from 111.9 to 177.1 cM. There was a significant linkage between the insertions/deletions and simple sequence repeat markers designed from the candidate intervals and the red/green skin (R/G) locus, which was in a 582.5-kb candidate interval that contained 81 predicted protein-coding gene models and was composed of two subintervals at the bottom of the fifth chromosome. The ZFRI 130-16, In2130-12 and In2130-16 markers located near the R/G locus could potentially be used to identify the red skin trait in Asian pear populations. This study provides new insights into the genetics controlling the red skin phenotype in this fruit.
Highlights
Pear, Pyrus L., is an important temperate fruit crop.[1]
Compared with European pear cultivars, there are few full red-skinned Asian pear cultivars,[4,9] and the red color usually appears on the side of the fruit that is exposed to the sun in these cultivars
Volz et al.[29] analyzed red skin color segregation ratios in 10 Asian pear hybrid families derived from ‘Huobali’ and suggested that genetic control of blush color in this cultivar may be due to the complimentary action of at least two dominant genes. These results indicate that the genetic basis and mechanism for red skin color may differ in Asian and European pear cultivars
Summary
Pyrus L. (tribe Maleae, subfamily Amygdaloideae, family Rosaceae), is an important temperate fruit crop.[1]. Pear fruit color is a major characteristic feature and is an important marketable trait.[2]. There is definite genetic governance of the trait, the extent of the red skin color of pear fruit is largely dependent on environmental conditions[10] and is primarily because of the presence of anthocyanins.[11,12,13] The biosynthesis and accumulation of anthocyanins are mainly determined by genetic factors and are influenced by light, temperature and other environmental factors.[14] The peak of anthocyanin biosynthesis occurs in the middle stage of fruit development in P. communis L. and some Asian pear cultivars[15,16,17] and at harvest in other Asian pear cultivars, a trend similar to that in apples.[18,19] In pears, most of the structural and regulatory genes in the anthocyanin biosynthetic pathway have been identified and functionally characterized.[20,21,22,23,24] Phenylalanine ammonia-lyase (PAL) and UDP-glucose: flavonoid-3O-glucosyltransferase (UFGT) participate in the first and final steps of anthocyanin biosynthesis, respectively. A study on two other red-skinned pear cultivars, ‘Meirensu’ and ‘Yunhongli No 1’, revealed that PAL induced anthocyanin biosynthesis and that UFGT was closely related to anthocyanin accumulation.[18]
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