Genome-wide association study identifies favorable SNP alleles and candidate genes for waterlogging tolerance in chrysanthemums

Abstract

Chrysanthemums are sensitive to waterlogging stress, and the development of screening methods for tolerant germplasms or genes and the breeding of tolerant new varieties are of great importance in chrysanthemum breeding. To understand the genetic basis of waterlogging tolerance (WT) in chrysanthemums, we performed a genome-wide association study (GWAS) using 92,811 single nucleotide polymorphisms (SNPs) in a panel of 88 chrysanthemum accessions, including 64 spray cut and 24 disbud chrysanthemums. The results showed that the average MFVW (membership function value of waterlogging) of the disbud type (0.65) was significantly higher than that of the spray type (0.55) at P < 0.05, and the MFVW of the Asian accessions (0.65) was significantly higher than that of the European accessions (0.48) at P  < 0.01. The GWAS performed using the general linear model (GLM) and mixed linear model (MLM) identified 137 and 14 SNP loci related to WT, respectively, and 11 associations were commonly predicted. By calculating the phenotypic effect values for 11 common SNP loci, six highly favorable SNP alleles that explained 12.85—21.85% of the phenotypic variations were identified. Furthermore, the dosage-pyramiding effects of the favorable alleles and the significant linear correlations between the numbers of highly favorable alleles and phenotypic values were identified ( r ² = 0.45; P < 0.01). A major SNP locus (Marker6619-75) was converted into a derived cleaved amplified polymorphic sequence (dCAPS) marker that cosegregated with WT with an average efficiency of 78.9%. Finally, four putative candidate genes in the WT were identified via quantitative real-time PCR (qRT-PCR). The results presented in this study provide insights for further research on WT mechanisms and the application of molecular marker-assisted selection (MAS) in chrysanthemum WT breeding programs.

Crop genetics: chrysanthemums that cope with water

Researchers in China have identified several genes that help chrysanthemum plants withstand waterlogging. Fadi Chen’s team at Nanjing Agricultural University used high-throughput sequencing to search for correlations between genetic mutations and waterlogging tolerance in 88 chrysanthemum varieties. One analysis method identified 137 mutations linked to waterlogging tolerance, while a second uncovered 14 mutations. Comparing the two lists revealed 11 mutations common to both. Six of these mutations could improve waterlogging response by 25%, and the team found that the mutations could be combined to improve performance even further. The team developed and tested a genetic marker to identify one of the high-tolerance mutations, demonstrating how this information may help breeders. They also identified four genes linked with the 137 mutations. Altogether, these findings point the way towards breeding chrysanthemums with greater waterlogging tolerance.