Drought is one of the most serious threats to crop production all over the world and is likely to worsen with anticipated changes in the climate. Drought impairs normal growth, disturbs water relations and reduces water-use efficiency in plants. Plants, however, have a variety of physiological and biochemical responses at cellular and organism levels, making it a more complex phenomenon. Researchers have been trying to understand and dissect the mechanisms of plant tolerance to drought stress using various approaches. The present chapter describes the strategies used by plants to adapt to low water potential at physiological, biochemical and molecular levels. This chapter also describes the strategies involving genetic engineering used by breeders in order to obtain crop varieties with improved drought tolerance, some of which show great promise. Modern genomic and genetic approaches coupled with breeding methodologies are expected to more effectively identify the genes and metabolic pathways that confer drought tolerance in crops.

Biotic and Abiotic Stress Tolerance in Plants

Pepper (Capsicum L.) is a nutritionally and economically important crop that is cultivated throughout the world as a vegetable, condiment, and food additive. Genetic transformation using Agrobacterium tumefaciens (agrobacterium) is a powerful biotechnology tool that could be used in pepper to develop community-based functional genomics resources and to introduce important agronomic traits. However, pepper is considered to be highly recalcitrant for agrobacterium-mediated transformation, and current transformation protocols are either inefficient, cumbersome or highly genotype dependent. The main bottleneck in pepper transformation is the inability to generate cells that are competent for both regeneration and transformation. Here, we report that ectopic expression of the Brassica napus BABY BOOM AP2/ERF transcription factor overcomes this bottleneck and can be used to efficiently regenerate transgenic plants from otherwise recalcitrant sweet pepper (C. annuum) varieties. Transient activation of BABY BOOM in the progeny plants induced prolific cell regeneration and was used to produce a large number of somatic embryos that could be converted readily to seedlings. The data highlight the utility of combining biotechnology and classical plant tissue culture approaches to develop an efficient transformation and regeneration system for a highly recalcitrant vegetable crop.

https://link.springer.com/content/pdf/10.1007%2Fs00299-011-1018-x.pdf

Efficient sweet pepper transformation mediated by the BABY BOOM transcription factor

The Capsicum genus is native to tropical America and consists of 27 species, five of which are used as fresh vegetables and spices: Capsicum annuum L., Capsicum chinense Jacq., Capsicum frutescens L., Capsicum baccatum L. and Capsicum pubescens R. et P. The study of the relationships among species of cultivate Capsicum species will be useful for breeding new cultivars or hybrids. This study is focused on the genetic diversity and relationships of these species that were collected in the Andean region. Ten microsatellites and four AFLP combinations were used to characterize 260 Capsicum accessions. The AFLP tree turned out to be informative regarding relationships among species. The data clearly showed the close relationships between C. chinense and C. frutescens. Moreover, C. cardenasii and C. eximium were indistinguishable as a single, morphologically variable species. Our data showed C. baccatum and C. praetermissum to be distinct species that form a compact group. In the present work, AFLP fingerprinting indicated that C. chacoense was placed in the C. baccatum complex and showed C. tovarii as a separate species. In addition, SSR data indicated that there is intraspecific differentiation in the species C. chinense, C. baccatum and C. pubescens, as the PCoA-based clustering showed a clear geographic division related to country. Even though Bolivia is considered to be the nuclear area for these species, we have found similar variability in Ecuador and Peru for several Capsicum species.

/pdf/taxonomy-and-genetic-diversity-of-domesticated-capsicum-2v9bq29kov.pdf

Taxonomy and genetic diversity of domesticated Capsicum species in the Andean region

Pepper (Capsicum spp.) is one of the most important vegetable crops; however, pepper genomic studies lag behind those of other important Solanaceae. Here we present the results of a high-throughput genotyping-by-sequencing (GBS) study of a collection of 190 Capsicum spp. accessions, including 183 of five cultivated species (C. annuum, C. chinense, C. frutescens, C. baccatum, and C. pubescens) and seven of the wild form C. annuum var. glabriusculum. Sequencing generated 6,766,231 high-quality read tags, of which 40.7% were successfully aligned to the reference genome. SNP calling yielded 4083 highly informative segregating SNPs. Genetic diversity and relationships of a subset of 148 accessions, of which a complete passport information was available, was studied using principal components analysis (PCA), discriminant analysis of principal components (DAPC), and phylogeny approaches. C. annuum, C. baccatum, and C. chinense were successfully separated by all methods. Our population was divided into seven clusters by DAPC, where C. frutescens accessions were clustered together with C. chinense. C. annuum var. glabriusculum accessions were spread into two distinct genetic pools, while European accessions were admixed and closely related. Separation of accessions was mainly associated to differences in fruit characteristics and origin. Phylogeny studies showed a close relation between Spanish and Mexican accessions, supporting the hypothesis that the first arose from a main genetic flow from the latter. Tajima's D statistic values were consistent with positive selection in the C. annuum clusters, possibly related to domestication or selection towards traits of interest. This work provides comprehensive and relevant information on the origin and relationships of Spanish landraces and for future association mapping studies in pepper.

/pdf/genetic-diversity-population-structure-and-relationships-in-3yw3yupbx4.pdf

Genetic diversity, population structure, and relationships in a collection of pepper (Capsicum spp.) landraces from the Spanish centre of diversity revealed by genotyping-by-sequencing (GBS).

Interspecific hybridization is essential to introgress resistance genes from Capsicum baccatum, a related species of cultivated pepper (C. annuum), since reliable genetic resources resistant to anthracnose have recently been identified within the C. baccatum germplasm. In conventional interspecific hybridization between the two species, hybrids could not be generated due to embryo abortion, which has been known to be a postfertilization genetic barrier. Some partially compatible cross combinations, determined through observations of embryo development after pollination, were identified using a large number of accessions of C. annuum as pistillate parents. Embryo rescue technique was successfully employed to produce hybrids in these partially compatible crosses. Immature seeds bearing torpedo or early cotyledonary embryos, developed 35–40 days after pollination, were excised and the embryos were cultured on MS medium with sucrose and plant growth regulators. Hybridity was confirmed by observation of corolla yellow spot as a dominant speciesspecific trait of C. baccatum and using random amplified polymorphic DNA (RAPD) marker analysis. All the hybrid plants displayed vigorous growth but complete pollen sterility. The hybrid sterility was overcome through intensive backcrossing using C. annuum as the pollen parent. Consequently, hundreds of interspecific BC1F1 progenies were raised, and introgression of anthracnose resistance was confirmed in this segregating population.

Overcoming Two Post-fertilization Genetic Barriers in Interspecific Hybridization between Capsicum annuum and C. baccatum for Introgression of Anthracnose Resistance

Pepper (Capsicum annuum L.) anthracnose, caused by Colletotrichum spp., is an important disease in many Asian countries. Recently, it was found that a local Korean variety, C. annuum ‘Daepoong-cho’, had resistance to C. capsici. Inheritance of resistance to C. capsici was analyzed in segregating populations derived from a cross of ‘Yeoju’ × ‘Daepoong-cho’. An allelism test was carried out in F1 and F2 progenies derived from the cross of ‘Daepoong-cho’ × ‘AR’. ‘AR’ is an anthracnose-resistant breeding line derived from C. chinense Jacq. ‘PBC 932’. Detached mature green fruits were inoculated using the microinjection method. Disease response was evaluated using disease incidence, overall lesion diameter, and true lesion diameter at 7 days after inoculation. The segregation ratios of resistance and susceptibility to C. capsici in F2 and BCR populations derived from the cross of ‘Yeoju’ × ‘Daepoong-cho’ were fitted to the 1 : 3 and 1 : 1 Mendelian model, respectively. This indicates that the resistance of ‘Daepoong-cho’ to C. capsici is controlled by a single recessive gene. The results of the allelism test indicated that the two resistant lines, ‘Daepoong-cho’ and ‘AR’, possessed the same resistance gene to C. capsici, even though the resistance genes of these two lines originated from different Capsicum species, C. annuum and C. chinense.

https://www.jstage.jst.go.jp/article/jsbbs/58/2/58_2_137/_pdf

A major recessive gene associated with anthracnose resistance to Colletotrichum capsici in chili pepper (Capsicum annuum L.)

The Capsicum genus includes 27 species; 5 domesticated and 22 wild ones. Among the 5 domesticated species, C. annuum is the most widely cultivated commercial species and thus, intensive breeding programs have been being carried out to improve this species worldwide. Recently, it has been reported that almost all traits needed for pepper breeding are mainly found in related or wild species of cultivated pepper (C. annuum). This experiment was carried out to determine interspecific crossability among 13 different genotypes of 5 cultivated species. The crosses of C. annuum with C. chinense or with C. frutescens were compatible or partial-compatible in many cases, although there were some differences in crossability among genotypes within the two parental species. In contrast, the crosses of C. annuum with C. baccatum or with C. pubescens were completely incompatible. The cause of incompatibility between C. annuum and C. baccatum was determined to be embryo and/or endosperm abortion. Several crosses determined as incompatible by the conventional crossability test were able to be re-determined as partial-compatible through an embryo rescue technique. Consequently, this experiment extended the boundary of breeding by interspecific hybridization in chili peppers.

Interspecific Cross Compatibility among Five Domesticated Species of Capsicum Genus

With 3 figures



Abstract

As one of the genic male sterility (GMS) materials in chili pepper (Capsicum annuum L.), GMS1 has been used for commercial F1 hybrid seed production. The male sterility of GMS1 is controlled by a recessive nuclear gene, named ms1. In this study, we developed DNA markers linked to the ms1 locus using a combination of bulked segregant analysis and amplified fragment length polymorphism (AFLP) in a segregating sibling population. From the screening of 1024 AFLP primer combinations, the AFLP marker E-AGC/M-GTG (514 bp) was identified as being linked to the ms1 locus at a distance of about 3 cM. Based on internal sequencing analysis of the E-AGC/M-GTG marker between male fertile and sterile plants, we identified three small deletions with a size of altogether 42 bp in the male-fertile plant and developed a codominant sequence characterized amplified region (SCAR) marker. This SCAR marker may be valuable for marker-assisted breeding in the hybrid seed production system of chili pepper using the GMS1 line.

A codominant SCAR marker linked to the genic male sterility gene (ms1) in chili pepper (Capsicum annuum)

Reliable genetic resources resistant to anthracnose, caused by Colletotrichum acutatum, in Capsicum have only been found in certain Capsicum species, e.g., Capsicum baccatum and C. chinense. Interspecific hybridization using embryo rescue was used to introgress anthracnose resistance from C. baccatum var. PBC81 into C. annuum var. Matikas. Because the interspecific hybrids were completely pollen-sterile, an interspecific BC₁F₁ as the first segregating population was raised through intensive backcrosses in which Matikas was used as the male parent. Among the hundreds of BC₁F₁ progeny, 88 plants setting many fruits were used to study inheritance of anthracnose resistance. The segregation of resistance to susceptibility in the BC₁F₁ population did not fit expected Mendelian ratios such as 1:1 or 3:1, and the frequency distribution of progenies varied continuously from resistant to susceptible. To estimate broad sense heritability of resistance, we used a real method of selection differential (i) and genetic gain (ΔG). According to the equation h²= ΔG/i, heritability was estimated as about 0.61. This result suggests that resistance of C. baccatum var. PBC81 can be controlled quantitatively, although we do not know yet how many genes are associated with the resistance.

Inheritance of Anthracnose (Colletotrichum acutatum) Resistance in Capsicum Using Interspecific Hybridization

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