Multiple genetic resistances in Capsicum spp

Ralstonia Strains from Potato-Growing Regions of Kenya Reveal Two Phylotypes and Epidemic Clonality of Phylotype II Sequevar 1 Strains

Bacterial wilt, caused by the Ralstonia solanacearum species complex (RSSC), is the most destructive potato disease in Kenya. Studies were conducted to (i) determine the molecular diversity of RSSC strains associated with bacterial wilt of potato in Kenya, (ii) generate an RSSC distribution map for epidemiological inference, and (iii) determine whether phylotype II sequevar 1 strains exhibit epidemic clonality. Surveys were conducted in 2018 and 2019, in which tubers from wilting potato plants and stem samples of potential alternative hosts were collected for pathogen isolation. The pathogen was phylotyped by multiplex PCR and 536 RSSC strains typed at a sequevar level. Two RSSC phylotypes were identified, phylotype II (98.4%, n = 506 [sequevar 1 (n = 505) and sequevar 2 (n = 1)]) and phylotype I (1.6%, n = 30 [sequevar 13 (n = 9) and a new sequevar (n = 21)]). The phylotype II sequevar 1 strains were haplotyped using multilocus tandem repeat sequence typing (TRST) schemes. The TRST scheme identified 51 TRST profiles within the phylotype II sequevar 1 strains with a modest diversity index (HGDI = 0.87), confirming the epidemic clonality of RSSC phylotype II sequevar 1 strains in Kenya. A minimum spanning tree and mapping of the TRST profiles revealed that TRST27 '8-5-12-7-5' is the primary founder of the clonal complex of RSSC phylotype II sequevar 1 and is widely distributed via latently infected seed tubers. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Phenotypic, molecular and pathogenic characterization of Colletotrichum scovillei infecting Capsicum species in Rio de Janeiro, Brazil

Anthracnose is a disease caused by Colletotrichum spp., one of the world’s most damaging sweet and chili pepper pathogens, especially in tropical and subtropical regions. In the state of Rio de Janeiro, anthracnose is one of the main obstacles for pepper crops. However, to date no research has focused on the identification and characterization of the pathogen, which is fundamental to understand the scope of the disease in the state. Thus, the correct identification of the fungal species and pathogenicity studies can provide important support for disease management and control, apart from identifying possible resistance sources for exploitation in peppers breeding programs. In this study, 11 Colletotrichum isolates were collected from peppers with typical symptoms in the Rio de Janeiro state. These isolates were characterized based on morpho-cultural characteristics and sequencing data from five regions (ITS, ACT, CAL, β-TUB and GAPDH), and the genetic variability was estimated by AFLP markers. Simultaneously, microscopy images of the colonization by the fungal species on unripe Capsicum annuum fruits were taken. Pathogenicity was tested and resistance sources were sought by means of infection of ripe and unripe fruits of 50 Capsicum baccatum accessions. The resulting data showed that all isolates belong to Colletotrichum scovillei specie. About the pathogenicity of Capsicum baccatum, differentiated, stage-specific responses, with higher resistance of ripe fruits were recorded. In addition, four possible sources of Colletotrichum scovillei resistance were detected among the tested accessions. The combination of these data can contribute to future studies on the interaction of Colletotrichum scovillei-Capsicum spp., a research line that is still unexploited in the main areas of this anthracnose fungus.

Capsidiol-related genes are highly expressed in response to Colletotrichum scovillei during Capsicum annuum fruit development stages

Capsicum annuum is one of the most important horticultural crops worldwide. Anthracnose disease (Colletotrichum spp.) is a major constraint for chili production, causing substantial losses. Capsidiol is a sesquiterpene phytoalexin present in pepper fruits that can enhance plant resistance. The genetic mechanisms involved in capisidiol biosynthesis are still poorly understood. In this study, a 3′ RNA sequencing approach was used to develop the transcriptional profile dataset of C. annuum genes in unripe (UF) and ripe fruits (RF) in response to C. scovillei infection. Results showed 4,845 upregulated and 4,720 downregulated genes in UF, and 2,560 upregulated and 1,762 downregulated genes in RF under fungus inoculation. Four capsidiol-related genes were selected for RT-qPCR analysis, two 5-epi-aristolochene synthase (CA12g05030, CA02g09520) and two 5-epi-aristolochene-1,3-dihydroxylase genes (CA12g05070, CA01g05990). CA12g05030 and CA01g05990 genes showed an early response to fungus infection in RF (24 h post-inoculation—HPI), being 68-fold and 53-fold more expressed at 96 HPI, respectively. In UF, all genes showed a late response, especially CA12g05030, which was 700-fold more expressed at 96 HPI compared to control plants. We are proving here the first high-throughput expression dataset of pepper fruits in response to anthracnose disease in order to contribute for future pepper breeding programs.

Biochemical analysis of antimicrobial peptides in two different Capsicum genotypes after fruit infection by Colletotrichum gloeosporioides

There are several phytosanitary problems that have been causing serious damage to the Capsicum crops, including anthracnose. Upon attack by certain pathogens, various protein molecules are produced, which are known as proteins related to pathogenesis (PR proteins), including antimicrobial peptides such as protease inhibitors, defensins and lipid transfer proteins (LTPs). The objective of this work is to identify antimicrobial proteins and/or peptides of two genotypes from Capsicum annuum fruits infected with Colletotrichum gloeosporioides. The fungus was inoculated into Capsicum fruits by the deposition of a spore suspension (10⁶ conidia ml⁻¹), and after 24 and 48 h intervals, the fruits were removed from the humid chamber and subjected to a protein extraction process. Protein analysis of the extracts was performed by tricine gel electrophoresis and Western blotting. The distinctive bands between genotypes in the electrophoresis profiles were subjected to mass spectrometry sequencing. Trypsin inhibition assays, reverse zymographic detection of protease inhibition and β-1,3-glucanase activity assays were also performed and extracts were also tested for their ability to inhibit the growth of C. gloeosporioides fungi ‘in vitro’. There were several low molecular weight proteins in all treated samples, and some treatments in which antimicrobial peptides such as defensin, lipid transfer protein (LTP) and protease inhibitor have been identified. It was shown that the green fruits are more responsive to infection, showing the production of antimicrobial peptides in response to injury and inoculation of the fungus, what did not occur in ripe fruits under any treatment.