Geleta Dugassa Barka

In this study, marker-assisted recurrent selection was evaluated for pyramiding resistance gene alleles against coffee leaf rust (CLR) and coffee berry diseases (CBD) in Coffea arabica. A total of 144 genotypes corresponding to 12 hybrid populations from crosses between eight parent plants with desired morphological and agronomic traits were evaluated. Molecular data were used for cross-certification, diversity study and resistance allele marker-assisted selection (MAS) against the causal agent of coffee leaf rust (Hemileia vastatrix) and coffee berry disease (Colletotrichum kahawae). In addition, nine morphological and agronomic traits were evaluated to determine the components of variance, select superior hybrids, and estimate genetic gain. From the genotypes evaluated, 134 were confirmed as hybrids. The genetic diversity between and within populations was 75.5% and 24.5%, respectively, and the cluster analysis revealed three primary groups. Pyramiding of CLR and CBD resistance genes was conducted in 11 genotypes using MAS. A selection intensity of 30% resulted in a gain of over 50% compared to the original population. Selected hybrids with increased gain also showed greater genetic divergence in addition to the pyramided resistance alleles. The strategies used were, therefore, efficient to select superior coffee hybrids for recurrent selection programs and could be used as a source of resistance in various crosses.

Genome-editing tools for the development of traits to tolerate abiotic and biotic adversaries are the recently devised breeding techniques revolutionizing molecular breeding by addressing the issues of rapidness and precision. To that end, disease resistance development by disrupting disease susceptibility genes (S genes) to intervene in the biological mechanism of pathogenicity has significantly improved the techniques of molecular breeding. Despite the achievements in genome-editing aimed at the intervention of the function of susceptibility determinants or gene regulatory elements, off-target effects associated with yield-related traits are still the main setbacks. The challenges are attributed to the complexity of the inheritance of traits controlled by pleiotropic genes. Therefore, a more rigorous genome-editing tool with ultra-precision and efficiency for the development of broad-spectrum and durable disease resistance applied to staple crop plants is of critical importance in molecular breeding programs. The main objective of this article is to review the most impressive progresses achieved in resistance breeding against the main diseases of three Solanaceae crops (potato, Solanum tuberosum; tomato, Solanum lycopersicum and pepper, Capsicum annuum) using genome-editing by disrupting the sequences of S genes, their promoters, or pathogen genes. In this paper, we discussed the complexity and applicability of genome-editing tools, summarized the main disease of Solanaceae crops, and compiled the recent reports on disease resistance developed by S-gene silencing and their off-target effects. Moreover, GO count and gene annotation were made for pooled S-genes from biological databases. Achievements and prospects of S-gene-based next-generation breeding technologies are also discussed.

Due to their perishable nature, tropical fruits are prone to pre-and post-harvest loss attributed to biotic and abiotic factors. Although the production of tropical fruits such as banana (Musa acuminata), guava (Psidium guajava), mango (Mangifera indica), papaya (Carica papaya), and passion fruit (Passiflora edulis) is in the increasing trend, the post-harvest loss remains a challenge for the production of excess tropical fruits worldwide. Severity and cross-pathogenicity of differentColletotrichumspecies attributed to the reasonable loss of such fruits, hence molecular detection and discrimination of such fungal species are indispensable for post-harvest disease management. In the present study, the rDNA ITS was used for molecular identification of fungal isolates from five tropical fruits at the post-harvesting stage. Most of the identified fungi belong to the genusColletotrichum. Furthermore, the cross-pathogenicity and disease symptom severity of the isolates across these fruit samples was also investigated. The result showed that most isolates are host-specific, passion fruit being the ideal host for all the discriminated isolates. The symptoms caused byColletotrichumisolates showed similar patterns as revealed by lesion diameter analysis. The work provided important data on the cross-pathogenicity and disease symptom characteristics ofColletotrichumpathogens known to affect the five tropical fruits investigated.

Potassium transporter genes are essential for plant salt stress tolerance. Identification of gene regulatory elements is vital for the recognition of gene expression patterns. Thus, understanding gene regulatory systems of potassium transporter genes is useful to improve the salt tolerance of crop plants. The present study was aimed at in silico analysis of promoter and regulatory elements of potassium transporter genes in coffee, peanut, soybean, maize, sorghum and potato crops. A total of 19 potassium transporter genes were identified, and the transcription start site (TSS), conserved motif, CpG islands were analysed using various computational tools. The highest promoter prediction score (1) was obtained in one gene sequence (LOC113728271) for Coffea arabica transcription start site, whereas the lowest score (0.8) was recorded in one gene sequence (LOC8065633) for Sorghum bicolor transcription start site. The analysis also showed that 66% of the genes contained more than one transcription start site whereas 63.16% had only one transcription start site. Five motifs were identified. Motif 1 was found as the common promoter motif residing on 78.95% of potassium transporter promoter sequences with an E-value of 3.4e − 002.C₂H₂ zinc finger transcription factors are predicted to bind to these conserved motifs with high statistical probability (2.28e − 03). Very few CpG islands were observed both in the promoter and body region of the gene sequences using two algorithms. The present study could contribute for better understanding of gene expression and the improvement of crops’ tolerance to environmental stresses through molecular assisted breeding or genetic engineering techniques.

The biotrophic fungus Hemileia vastatrix causes coffee leaf rust (CLR), one of the most devastating diseases in Coffea arabica . Coffee, like other plants, has developed effective mechanisms to recognize and respond to infections caused by pathogens. Plant resistance gene analogs (RGAs) have been identified in certain plants as candidates for resistance ( R ) genes or membrane receptors that activate the R genes. The RGAs identified in different plants possess conserved domains that play specific roles in the fight against pathogens. Despite the importance of RGAs, in coffee plants these genes and other molecular mechanisms of disease resistance are still unknown. This study aimed to sequence and characterize candidate genes from coffee plants with the potential for involvement in resistance to H. vastatrix . Sequencing was performed based on a library of bacterial artificial chromosomes (BAC) of the coffee clone ‘Híbrido de Timor’ (HdT) CIFC 832/2 and screened using a functional marker. Two RGAs, HdT_LRR_RLK1 and HdT_LRR_RLK2, containing the motif of leucine-rich repeat-like kinase (LRR-RLK) were identified. Based on the presence or absence of the HdT_LRR_RLK2 RGA in a number of differential coffee clones containing different combinations of the rust resistance gene, these RGAs did not correspond to any resistance gene already characterized (SH1-9). These genes were also analyzed using qPCR and demonstrated a major expression peak at 24 h after inoculation in both the compatible and incompatible interactions between coffee and H. vastatrix . These results are valuable information for breeding programs aimed at developing CLR-resistant cultivars, in addition to enabling a better understanding of the interactions between coffee and H. vastatrix .

Diabetes mellitus, a group of metabolic disorders characterized by hyperglycemia, is one of the most serious and common diseases around the world and is associated with major complications such as diabetic neuropathy, retinopathy, and cardiovascular diseases. A widely used treatment for non-insulin-dependent diabetes is α-glucosidase inhibitors (AGIs) such as acarbose, which hinders hydrolytic cleavage of disaccharides and retard glucose absorption. The ability to inhibit α-glucosidase activity has been reported in leaf and fruit of pepper (Capsicum annuum L.). In this study, we aimed to identify quantitative trait loci (QTLs) controlling α-glucosidase inhibitory activity (AGI activity) in pepper leaf and fruit using enzyme assay and genotyping-by-sequencing (GBS) analysis. The AGI activity at three stages of leaf and one stage of fruit development was analyzed by 96 F₂ individuals. GBS analysis identified 17,427 SNPs that were subjected to pepper genetic linkage map construction. The map, consisting of 763 SNPs, contained 12 linkage groups with a total genetic distance of 2379 cM. QTL analysis revealed seven QTLs (qAGI1.1, qAGI11.1, qAGI5.1, qAGI9.1, qAGI12.1, qAGI5.2, and qAGI12.2) controlling AGI activity in pepper leaf and fruit. The QTLs for AGI activity varied by plant age and organ. This QTL information is expected to provide a significant contribution to developing pepper varieties with high AGI activity.

Physiology-based differentiation of S_H genes and Hemileia vastatrix races is the principal method employed for the characterization of coffee leaf rust resistance. Based on the gene-for-gene theory, nine major rust resistance genes (S_H1-9) have been proposed. However, these genes have not been characterized at the molecular level. Consequently, the lack of molecular data regarding rust resistance genes or candidates is a major bottleneck in coffee breeding. To address this issue, we screened a BAC library with resistance gene analogs (RGAs), identified RGAs, characterized and explored for any S_H related candidate genes. Herein, we report the identification and characterization of a gene (gene 11), which shares conserved sequences with other S_H genes and displays a characteristic polymorphic allele conferring different resistance phenotypes. Furthermore, comparative analysis of the two RGAs belonging to CC-NBS-LRR revealed more intense diversifying selection in tomato and grape genomes than in coffee. For the first time, the present study has unveiled novel insights into the molecular nature of the S_H genes, thereby opening new avenues for coffee rust resistance molecular breeding. The characterized candidate RGA is of particular importance for further biological function analysis in coffee.

The original version of this article unfortunately contained two mistakes in the “Materials and methods” section, subsection “DNA extraction and PCR” of the article. The correct information is given...

Physiology-based differentiation of S _H genes and Hemileia vastatrix races is the principal method employed for the characterization of coffee leaf rust resistance. Based on the gene-for-gene theory, nine major rust resistance genes (S _H 1-9) have been proposed. However, these genes have not been characterized at the molecular level. Consequently, the lack of molecular data regarding rust resistance genes or candidates is a major bottleneck in coffee breeding. To address this issue, we screened a BAC library with resistance gene analogs (RGAs), identified RGAs, characterized and explored for any S _H related candidate genes. Herein, we report the identification and characterization of a gene (gene 11), which shares conserved sequences with other S _H genes and displays a characteristic polymorphic allele conferring different resistance phenotypes. Furthermore, comparative analysis of the two RGAs belonging to CC-NBS-LRR revealed more intense diversifying selection in tomato and grape genomes than in coffee. For the first time, the present study has unveiled novel insights into the molecular nature of the S _H genes, thereby opening new avenues for coffee rust resistance molecular breeding. The characterized candidate RGA is of particular importance for further biological function analysis in coffee.