Development and Validation of KASP Markers Based on a Whole- Genome Resequencing Approach in a Hybrid Population of Luli × Red No. 1

A series of kompetitive allele-specific PCR (KASP) markers for traits related to apple leaves were developed to provide a reference to effectively utilize light in apple breeding using a Luli ×Red No. 1 hybrid population as materials.

This study investigated the leaf trait phenotypic data (including leaf length, width, contents of chlorophyll and anthocyanin, photosynthetic rate and chlorophyll fluorescence parameters) of Luli, a type I red-fleshed apple, Red No. 1, and 134 hybrids. Whole-genome resequencing was conducted on an Illumina HiSeq 2500 platform. The clean sequencing reads were mapped to the apple reference genome using BWA software. GATK software was used to identify single nucleotide polymorphisms (SNPs).

A total of 164 776 660, 149 482 876, and 3 927 370 200 clean reads were obtained by whole-genome resequencing from Luli, Red No. 1 and 134 hybrid individuals, respectively. The data were aligned to the reference genome sequences with mapping rates of 98.77%, 98.89%, and 97.79%, respectively. A total of 6 445 766 SNPs were identified. The SNPs were then filtered, and 94 208 accurate and high-quality SNPs were selected for subsequent KASP primer design. Finally, 5 802 KASP markers were developed based on a high-throughput whole-genome resequencing approach. The average polymorphism information content (PIC) of these KASP markers was 0.31, and there were 30.13% PICs>0.35. The Simpson genetic diversity index ranged from 0.01 to 0.67, with an average value of 0.53. The mean observed heterozygosity was 0.32. A Kyoto Encyclopedia of Genes and Genomes enrichment analysis of the genes for KASP marker revealed that “one carbon pool by folate” was the most significant pathway. An analysis of the phenotypic data of leaf-related traits in both the parents and individuals from the Luli ×Red No. 1 cross showed that there were significant differences in the phenotypic values of leaf net photosynthetic rate, stomatal conductance (Gs) and other traits between the parents Luli and Red No. 1. The F1 generation exhibited a wide phenotypic variation, and the most traits segregated extensively. Α detailed study of the phenotypic data of leaf traits of the hybrid population with the genotype and annotations of the KASP markers finally resulted in the development of 21 KASP markers, which was correlated with leaf-related traits, including chlorophyll content, Gs and leaf length and width.

Use of the whole-genome resequencing data of Luli, Red No. 1 and 134 hybrid individuals resulted in the development of 5 802 KASP. A total of 21 of these KASP markers significantly correlated with leaf traits, which provided a theoretical reference for the high utilization of light energy in apple breeding.