Mapping of fruit length related QTLs in interspecific cross (Capsicum annuum L. × Capsicum galapagoense Hunz.) of chilli

Identification of Fruit Traits Related QTLs and a Candidate Gene, CaBRX, Controlling Locule Number in Pepper (Capsicum annuum L.)

Fruit traits are important in pepper (Capsicum annuum L.) and affect its quality and yield. These traits are controlled by quantitative trait loci (QTLs). In this study, we identified many major QTLs that control fruit length (Ftl), fruit diameter (Ftd), fruit shape (Fts), fruit weight (Ftw) and locule number (Lcn) in the F2 and F2:3 populations developed from the QTL mapping of GS6 (P1) and Qiemen (P2). A total of 111 simple sequence repeats and insertion/deletion markers were utilized to construct a linkage map with 12 linkage groups over a length of 1320.72 cM. An inclusive composite interval mapping analysis indicated that many QTLs were detected and included ftl2.1, ftd2.1, fts1.1, ftw2.1 and lcn1.1. As a novel QTL, lcn1.1 was located between HM1112 and EPMS709, and the genetic distance was 3.18 cM covering 60 predicted genes. Within the region, we identified Capana01g004285 as a candidate gene by functional annotation and expression analysis and found that it encodes the BREVIS RADIX (BRX) protein. Knockdown of CaBRX through the virus-induced gene silencing approach in GS6 reduced the number of locules and influenced the expressions of genes related to flower and locule development, suggesting that CaBRX plays an important function in the development of locules.

Molecular mapping of dominant gene responsible for leaf curl virus resistance in chilli pepper (Capsicum annuum L.)

A resistant source (S-343) having monogenic dominant resistance to chilli leaf curl virus disease (ChiLCVD) has been identified at Punjab Agricultural University (PAU), Ludhiana. The F₂ mapping population of 204 plants was derived from the cross MS-341 (susceptible) × S-343 (resistant) to identify the linked marker with the disease-resistant gene. Out of the 685 single-sequence repeats (SSRs) used, only 160 primers showed parental polymorphism. These 160 polymorphic primers were used for bulk segregant analysis and only eight SSR primers were able to differentiate the resistant and susceptible bulks. The linkage analysis revealed that the two markers CA 516044 and PAU-LC-343-1 were found linked with the disease-resistant gene covering a total distance of 15.7 centimorgan (cM). The two primers CA 516044 and PAU-LC-343-1 were found located on chromosome 6 of the pepper genome at a genetic distance of 6.8 cM and 8.9 cM, respectively, from the resistant gene. The validation of linked markers was performed using 26 resistant and susceptible genotypes developed at PAU, Ludhiana by former researchers. The validation of the primers revealed that there was a correlation between phenotypic and genotypic data of the used genotypes, and these markers can be used for the marker-assisted breeding procedures for transferring ChiLCVD resistance until the gene-based markers will be developed. The markers described in this study are the first-ever molecular markers identified as linked to the ChiLCVD-resistant gene.

Genomic diversity and novel genome-wide association with fruit morphology in Capsicum, from 746k polymorphic sites

Capsicum is one of the major vegetable crops grown worldwide. Current subdivision in clades and species is based on morphological traits and coarse sets of genetic markers. Broad variability of fruits has been driven by breeding programs and has been mainly studied by linkage analysis. We discovered 746k variable sites by sequencing 1.8% of the genome in a collection of 373 accessions belonging to 11 Capsicum species from 51 countries. We describe genomic variation at population-level, confirm major subdivision in clades and species, and show that the known major subdivision of C. annuum separates large and bulky fruits from small ones. In C. annuum, we identify four novel loci associated with phenotypes determining the fruit shape, including a non-synonymous mutation in the gene Longifolia 1-like (CA03g16080). Our collection covers all the economically important species of Capsicum widely used in breeding programs and represent the widest and largest study so far in terms of the number of species and number of genetic variants analyzed. We identified a large set of markers that can be used for population genetic studies and genetic association analyses. Our results provide a comprehensive and precise perspective on genomic variability in Capsicum at population-level and suggest that future fine genetic association studies will yield useful results for breeding.