Genomic selection of eight fruit traits in pear

Genomic selection (GS) has the potential to improve selection efficiency and shorten the breeding cycle in fruit tree breeding. In this study,we evaluated the effect of prediction methods, marker density and the training population (TP) size on pear GS for improving its performance and reducing cost. We evaluated GS under two scenarios:(1) five-fold cross-validation in an interspecific pear family;(2) independent validation. Based on the cross-validation scheme, the prediction accuracy (PA) of eight fruit traits varied between 0.33 (fruit core vertical diameter)and 0.65 (stone cell content). Except for single fruit weight, a slightly better prediction accuracy (PA) was observed for the five parametrical methods compared with the two non-parametrical methods. In our TP of 310 individuals, 2 000 single nucleotide polymorphism (SNP) markers were sufficient to make reasonably accurate predictions. PAs for different traits increased by 18.21%-46.98%when the TP size increased from 50to 100, but the increment was smaller (-4.13%-33.91%) when the TP size increased from 200 to 250. For independent validation, the PAs ranged from 0.11 to 0.45 using rrBLUP method. In summary, our results showed that the TP size and SNP numbers had a greater impact on the PA than prediction methods. Furthermore, relatedness among the training and validation sets, and the complexity of traits should be considered when designing a TP to predict the test panel.

Fine-mapping and validation of the genomic region underpinning pear red skin colour

Red skin colour is an important target trait in various pear breeding programmes.In this study,the genetic control of red skin colour was investigated in an interspecific population derived using the descendants of the red sport European pear cultivar‘Max Red Bartlett’(MRB)and the red-blushed Chinese pear cultivar‘Huobali’.Approximately 550 seedlings from nine families were phenotyped for red skin over-colour coverage(Ocolcov)and the intensity of red over-colour(Ocolint)on a 0–9 scale,and genotyped using genotyping-by-sequencing.Genome-wide association analyses were conducted using 7500 high-quality single nucleotide polymorphisms(SNPs).Genomic regions on linkage groups(LG)4 and 5 were found to be associated,and the best SNP(S578_25116)on LG4 accounted for~15%of phenotypic variation in Ocolcov and Ocolint.The association of S578_25116 with Ocolcov and Ocolint was successfully validated in a sample of~200 European and Asian pear accessions.The association with red skin at locus S578_25116 was not present in Asian pear accessions,suggesting its close proximity to the MRB’s Cardinal gene.Several putative candidate genes,including MYB transcription factors(PCP027962 and PCP027967),were identified in the quantitative trait locus region on LG4 and await functional validation.