Genomic regions and candidate genes linked with Phytophthora capsici root rot resistance in chile pepper (Capsicum annuum L.)

Abstract

Background: Phytophthora root rot, caused by Phytophthora capsici, is a major disease affecting Capsicum production worldwide. A recombinant inbred line (RIL) population derived from the hybridization between 'Criollo de Morellos-334' (CM-334), a resistant landrace from Mexico, and 'Early Jalapeno', a susceptible cultivar was genotyped using genotyping-by-sequencing (GBS)-derived single nucleotide polymorphism (SNP) markers. A GBS-SNP based genetic linkage map for the RIL population was constructed. Quantitative trait loci (QTL) mapping dissected the genetic architecture of P. capsici resistance and candidate genes linked to resistance for this important disease were identified.

Results: Development of a genetic linkage map using 1,973 GBS-derived polymorphic SNP markers identified 12 linkage groups corresponding to the 12 chromosomes of chile pepper, with a total length of 1,277.7 cM and a marker density of 1.5 SNP/cM. The maximum gaps between consecutive SNP markers ranged between 1.9 (LG7) and 13.5 cM (LG5). Collinearity between genetic and physical positions of markers reached a maximum of 0.92 for LG8. QTL mapping identified genomic regions associated with P. capsici resistance in chromosomes P5, P8, and P9 that explained between 19.7 and 30.4% of phenotypic variation for resistance. Additive interactions between QTL in chromosomes P5 and P8 were observed. The role of chromosome P5 as major genomic region containing P. capsici resistance QTL was established. Through candidate gene analysis, biological functions associated with response to pathogen infections, regulation of cyclin-dependent protein serine/threonine kinase activity, and epigenetic mechanisms such as DNA methylation were identified.

Conclusions: Results support the genetic complexity of the P. capsici-Capsicum pathosystem and the possible role of epigenetics in conferring resistance to Phytophthora root rot. Significant genomic regions and candidate genes associated with disease response and gene regulatory activity were identified which allows for a deeper understanding of the genomic landscape of Phytophthora root rot resistance in chile pepper.

Keywords: Genotyping-by-sequencing; New Mexico RIL (NMRIL) population; Phytophthora root rot; QTL mapping; Single nucleotide polymorphisms.

Fig. 1

Distribution of mean disease scores (a) and area under disease progress curve (AUDPC) (b) from 2-14 days post-infection for the New Mexico RIL population inoculated with Phytophthora capsici. CM-334, NMCA 10399, and Camelot are the resistant and susceptible controls 1 and 2, respectively. Bars indicate standard errors. Blue solid curve represents the test for normality using the Shapiro-Wilk test

Fig. 2

Distribution of SNP markers across the 12 chromosomes of chile pepper (Capsicum annuum). SNP-B set comprised of 7,247 markers polymorphic for the parental lines (CM-334 and ‘Early Jalapeno’). SNP-C set consisted of 1,973 polymorphic markers with no segregation distortion and was used to construct the linkage map

Fig. 3

SNP-based genetic linkage map for the New Mexico Recombinant Inbred Line (NMRIL) population using 1,973 markers. Black bars indicate SNP marker loci

Fig. 4

Effect plots for the Phytophthora capsici resistance QTL identified on chromosomes P5 and P8 showing additive interactions. SNP_3138 (SCM002816.1_34981103; chromosome P5) showed additive interaction with SNP_4697 (SCM002819.1_132653758; chromosome P8) whereas SNP_4695 (SCM002819.1_13265375; chromosome P8) demonstrated additive interaction with SNP_4701 (SCM002819.1_133538774; chromosome P8) (Table 2). AA allele = CM-334; resistant parent; BB allele= Early Jalapeno, susceptible parent)