Development and validation of KASP markers for resistance to Phytophthora capsici in Capsicum annuum L.

Resistance of Capsicum annuum to Phytophthora blight is dependent on the genetic background of the resistance source and the Phytophthora capsici isolate, which poses challenges for development of generally applicable molecular markers for marker-assisted selection. In this study, the resistance to P. capsici of C. annuum was genetically mapped to chromosome 5 within a 1.68-Mb interval by genome-wide association study analysis of 237 accessions. In this candidate region, 30 KASP markers were developed using genome resequencing data for a P. capsici-resistant line (0601 M) and a susceptible line (77,013). Seven of these KASP markers, located in the coding region of a probable leucine-rich repeats receptor-like serine/threonine-protein kinase gene (Capana05g000704), were validated in the 237 accessions, which showed an average accuracy of 82.7%. The genotyping of the seven KASP markers strongly corresponded with the phenotype of 42 individual plants in a pedigree family (PC83-163) developed from the P. capsici-resistant line CM334. This research provides a set of efficient and high-throughput KASP markers for marker-assisted selection of resistance to P. capsici in C. annuum. Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-023-01367-3.

Pepper variome reveals the history and key loci associated with fruit domestication and diversification.

Pepper (Capsicum spp.) is an important vegetable crop that provides a unique pungent sensation when eaten. Through construction of a pepper variome map, we examined the main groups that emerged during domestication and breeding of C. annuum, their relationships and temporal succession, and the molecular events underlying the main transitions. The results showed that the initial differentiation in fruit shape and pungency, increase in fruit weight, and transition from erect to pendent fruits, as well as the recent appearance of large, blocky, sweet fruits (bell peppers), were accompanied by strong selection/fixation of key alleles and introgressions in two large genomic regions. Furthermore, we identified Up, which encodes a BIG GRAIN protein involved in auxin transport, as a key domestication gene that controls erect vs pendent fruit orientation. The up mutation gained increased expression especially in the fruit pedicel through a 579-bp sequence deletion in its 5' upstream region, resulting in the phenotype of pendent fruit. The function of Up was confirmed by virus-induced gene silencing. Taken together, these findings constitute a cornerstone for understanding the domestication and differentiation of a key horticultural crop.

Fine mapping of Rf2, a minor Restorer-of-fertility (Rf) gene for cytoplasmic male sterility in chili pepper G164 (Capsicum annuum L.).

KEY MESSAGE: Genome re-sequencing and recombination analyses identified Capana06g000193 as a strong candidate for the minor male fertility restoration locus Rf2 in chili pepper G164 harboring two dominant male fertility restoration genes. Male fertility restoration genes of chili pepper restorer line G164 (Capsicum annuum L.) were studied using molecular marker genotypes of an F2 population (7G) of G164 crossed with the cytoplasmic male sterility line 77013A. The ratio of sterile to fertile single plants in the F2 population was 1:15. This result indicates that chili pepper G164 has two dominant restoration genes, which we designated as Rf1 and Rf2. An individual plant recessive for Rf1 and heterozygous for Rf2, 7G-112 (rf1rf1Rf2rf2), was identified by molecular marker selection and genetic analysis, and a single Rf2 gene-segregating population with a 3:1 ratio of fertile to sterile plants was developed from the self-pollination of male fertile individuals of 77013A and 7G-112 hybrid progeny. Bulk segregant analysis of fertile and sterile pools from the segregating populations was used to genetically map Rf2 to a 3.1-Mb region on chromosome 6. Rf2 was further narrowed to a 179.3-kb interval through recombination analysis of molecular markers and obtained the most likely candidate gene, Capana06g000193.

Development and application of KASP markers associated with Restorer-of-fertility gene in Capsicum annuum L.

Fertility restoration of cytoplasmic male sterility (CMS) in Capsicum annuum is controlled by multiple alleles of Restorer-of-fertility (Rf) genes. The isolation of additional Rf genes should therefore enrich the knowledge of CMS/Rf systems and accelerate their exploitation in hybrid seed production. In this study, the fertility restorer gene CaRfm of '0601 M', a non-pungent bell pepper, was genetically mapped to a 1.2-cM region flanked by KASP markers S761 and S183. CaRfm was then physically mapped to a 128.96-Kb interval predicted from 24 recombinants with two co-segregated markers, S423 and S424. CaPPR6 encoding a pentatricopeptide repeat (PPR) protein was suggested as the most likely candidate gene for the CaRfm locus on the basis of sequence alignment as well as genotyping of tightly linked markers. In addition, molecular markers S1597 and S1609, which are immediately adjacent to CaRfm at 15.7 and 57.8-Kb respectively, were developed and applied to marker-assisted selection. The results provided friendly markers for breeding pepper restorer lines and laid the foundation for elucidating the male fertility restoration mechanism. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12298-021-01109-9.

Compression Characteristics and Microscopic Mechanism of Coastal Soil Modified with Cement and Fly Ash.

It is of great significance to study the consolidation characteristics of modified coastal cement-soil. A one-dimensional consolidation test and microscopic test were carried out. In the tests, the cement content was 20%, fly ash content was 0%, 5%, 10%, 20%, and 30%, and the water content was 80%. The consolidation test results showed that: (1) Compared with coastal cement soil, the deformation of coastal cement soil modified with a 20% fly ash content was reduced from 4.31 to 2.70 mm, and the vertical compression deformation was reduced by 1.61 mm. (2) During consolidation and compression, the e-p curve (pore ratio-pressure curve) of fly ash-modified coastal cement soil was slower than that of coastal cement soil and the rate of change of pore ratio. (3) The compression coefficient of fly ash-modified coastal cement soil was reduced from 0.780 to 0.598 MPa-1 compared with that of coastal cement soil. The microscopic test results indicate that after adding the proper amount of fly ash, a skeleton was formed between the microscopic particles of the sample, which improved its resistance to compression and deformation. The results of this study indicate that it is feasible to modify coastal cement soil with an appropriate amount of fly ash to improve its compression resistance.

Expression of grape ACS1 in tomato decreases ethylene and alters the balance between auxin and ethylene during shoot and root formation.

Ethylene plays an important role in the grape rachis, where its production can be 10 times higher than in the berry. VvACS1 is the only rachis-specific ACC synthase (ACS) gene, and its expression is coincident with ethylene production in the rachis of Vitis vinifera 'Thompson seedless'. VvACS1 was cloned and ectopically expressed in tomato (Solanum lycopersicum 'Moneymaker'). Lateral buds were increased in two- or four-week-old 35s∷VvACS1 transgenic tomato plants after transplanting. Compared with wild-type (WT) plants, the transgenic tomato plants showed higher expression of the VvACS1 gene in the flowers, leaves, rachis, and fruits. There was no obvious difference of ACS activity in the fruit of tomato, and only increased ACS activity in the rachis of tomato. Ethylene production was decreased in flowers, leaves, and fruits (seven weeks after full bloom), while the relative expression of endogenous tomato ACS1 and ACS6 genes was not down-regulated by the ectopic expression of VvACS1. These results imply that post-transcriptional or post-translational regulation of ACS may occur, resulting in lower ethylene production in the transgenic tomato plants. Moreover, expression of VvACS1 in tomato resulted in decreased auxin and increased zeatin contents in the lateral buds, as well as reduced or delayed formation of adventitious roots in lateral bud cuttings. RNA-Seq and qRT-PCR analyses of rooted lateral bud cuttings indicated that the relative expression levels of the genes for zeatin O-glucosyltransferase-like, auxin repressed/dormancy-associated protein, and ERF transcription factors were higher in transgenic tomatoes than in WT, suggesting that ethylene may regulate auxin transport and distribution in shoots and that adventitious root formation employs coordination between auxin and ethylene.