Fungal Pathogens in Grasslands

Diversity of Leaf Fungal Endophytes from Two Coffea arabica Varieties and Antagonism towards Coffee Leaf Rust

Coffee has immense value as a worldwide-appreciated commodity. However, its production faces the effects of climate change and the spread of severe diseases such as coffee leaf rust (CLR). The exploration of fungal endophytes associated with Coffea sp. has already found the existence of nearly 600 fungal species, but their role in the plants remains practically unknown. We have researched the diversity of leaf fungal endophytes in two Coffea arabica varieties: one susceptible and one resistant to CLR. Then, we conducted cross-infection essays with four common endophyte species (three Colletotrichum sp. and Xylaria sp. 1) and Hemileia vastatrix (CLR) in leaf discs, to investigate the interaction of the endophytes on CLR colonisation success and severity of infection. Two Colletotrichum sp., when inoculated 72 h before H. vastatrix, prevented the colonisation of the leaf disc by the latter. Moreover, the presence of endophytes prior to the arrival of H. vastatrix ameliorated the severity of CLR. Our work highlights both the importance of characterising the hidden biodiversity of endophytes and investigating their potential roles in the plant-endophyte interaction.

Essential Oils and Antagonistic Microorganisms as Eco-Friendly Alternatives for Coffee Leaf Rust Control

Coffee leaf rust (CLR) is caused by the biotrophic fungus Hemileia vastatrix Berk. & Br., a disease of economic importance, reducing coffee yield up to 60%. Currently, CLR epidemics have negatively impacted food security. Therefore, the objective of the present research study is to show a current framework of this disease and its effects on diverse areas, as well as the biological systems used for its control, mode of action, and effectiveness. The use of essential plant oils and antagonistic microorganisms to H. vastatrix are highlighted. Terpenes, terpenoids, and aromatic compounds are the main constituents of these oils, which alter the cell wall and membrane composition and modify the basic cell functions. Beneficial microorganisms inhibit urediniospore germination and reduce disease incidence and severity. The antagonistic microorganisms and essential oils of some aromatic plants have great potential in agriculture. These biological systems may have more than one mechanism of action, which reduces the possibility of the emergence of resistant strains of H. vastatrix.

Multi-Locus Phylogenetic Analysis Revealed the Association of Six Colletotrichum Species with Anthracnose Disease of Coffee (Coffea arabica L.) in Saudi Arabia

Several Colletotrichum species are able to cause anthracnose disease in coffee (Coffea arabica L.) and occur in all coffee production areas worldwide. A planned investigation of coffee plantations was carried out in Southwest Saudi Arabia in October, November, and December 2022. Various patterns of symptoms were observed in all 23 surveyed coffee plantations due to unknown causal agents. Isolation from symptomatic fresh samples was performed on a PDA medium supplemented with streptomycin sulfate (300 mg L^-1) and copper hydroxide (42.5 mg L^-1). Twenty-seven pure isolates of Colletotrichum-like fungi were obtained using a spore suspension method. The taxonomic placements of Colletotrichum-like fungi were performed based on the sequence dataset of multi-loci of internal transcribed spacer region rDNA (ITS), chitin synthase I (CHS-1), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), actin (ACT), β-tubulin (TUB2), and partial mating type (Mat1-2) (ApMat) genes. The novel species are described in detail, including comprehensive morphological characteristics and colored illustrations. The pathogenicity of the isolated Colletotrichum species was assessed on detached coffee leaves as well as green and red fruit under laboratory conditions. The multi-locus phylogenetic analyses of the six-loci, ITS, ACT, CHS-1, TUB2, GAPDH and ApMat, revealed that 25 isolates were allocated within the C. gloeosporioides complex, while the remaining two isolates were assigned to the C. boninense complex. Six species were recognized, four of them, C. aeschynomenes, C. siamense, C. phyllanthi, and C. karstii, had been previously described. Based on molecular analyses and morphological examination comparisons, C. saudianum and C. coffeae-arabicae represent novel members within the C. gloeosporioides complex. Pathogenicity investigation confirmed that the Colletotrichum species could induce disease in coffee leaves as well as green and red fruits with variations. Based on the available literature and research, this is the first documentation for C. aeschynomenes, C. siamense, C. karstii, C. phyllanthi, C. saudianum, and C. coffeae-arabicae to cause anthracnose on coffee in Saudi Arabia.

Morphological and Phylogenetic Characterisations Reveal Four New Species in Leptosphaeriaceae (Pleosporales, Dothideomycetes)

Leptosphaeriaceae is a widely distributed fungal family with diverse lifestyles. The family includes several genera that can be distinguished by morphology and molecular phylogenetic analysis. During our investigation of saprobic fungi on grasslands in Yunnan Province, China, four fungal taxa belonging to Leptosphaeriaceae associated with grasses were collected. Morphological observations and phylogenetic analyses of the combined SSU, LSU, ITS, tub2, and rpb2 loci based on maximum likelihood and Bayesian inference were used to reveal the taxonomic placement of these fungal taxa. This study introduces four new taxa, viz. Leptosphaeria yunnanensis, L. zhaotongensis, Paraleptosphaeria kunmingensis, and Plenodomus zhaotongensis. Colour photo plates, full descriptions, and a phylogenetic tree to show the placement of the new taxa are provided.

Thermal Contaminants in Coffee Induced by Roasting: A Review

Roasting is responsible for imparting the main characteristics to coffee, but the high temperatures used in the process can lead to the formation of several potentially toxic substances. Among them, polycyclic aromatic hydrocarbons, acrylamide, furan and its derivative compounds, α-dicarbonyls and advanced glycation end products, 4-methylimidazole, and chloropropanols stand out. The objective of this review is to present a current and comprehensive overview of the chemical contaminants formed during coffee roasting, including a discussion of mitigation strategies reported in the literature to decrease the concentration of these toxicants. Although the formation of the contaminants occurs during the roasting step, knowledge of the coffee production chain as a whole is important to understand the main variables that will impact their concentrations in the different coffee products. The precursors and routes of formation are generally different for each contaminant, and the formed concentrations can be quite high for some substances. In addition, the study highlights several mitigation strategies related to decreasing the concentration of precursors, modifying process conditions and eliminating/degrading the formed contaminant. Many of these strategies show promising results, but there are still challenges to be overcome, since little information is available about advantages and disadvantages in relation to aspects such as costs, potential for application on an industrial scale and impacts on sensory properties.

Comparative transcriptomic analysis of the gene expression and underlying molecular mechanism of submergence stress response in orchardgrass roots

INTRODUCTION

Submergence stress creates a hypoxic environment. Roots are the first plant organ to face these low-oxygen conditions, which causes damage and affects the plant growth and yield. Orchardgrass (Dactylis glomerata L.) is one of the most important cold-season forage grasses globally. However, their submergence stress-induced gene expression and the underlying molecular mechanisms of orchardgrass roots are still unknown.

METHODS

Using the submergence-tolerant 'Dianbei' and submergence-sensitive 'Anba', the transcriptomic analysis of orchardgrass roots at different time points of submergence stress (0 h, 8 h, and 24 h) was performed.

RESULTS

We obtained 118.82Gb clean data by RNA-Seq. As compared with the control, a total of 6663 and 9857 differentially expressed genes (DEGs) were detected in Dianbei, while 7894 and 11215 DEGs were detected in Anba at 8 h and 24 h post-submergence-stress, respectively. Gene Ontology (GO) enrichment analysis obtained 986 terms, while Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis obtained 123 pathways. Among them, the DEGs in plant hormones, mitogen-activated protein kinase (MAPK) and Ca²⁺ signal transduction were significantly differentially expressed in Dianbei, but not in Anba.

DISCUSSION

This study was the first to molecularly elucidate the submergence stress tolerance in the roots of two orchardgrass cultivars. These findings not only enhanced our understanding of the orchardgrass submergence tolerance, but also provided a theoretical basis 36 for the cultivation of submergence-tolerant forage varieties.

Soil Mycobiome Diversity under Different Tillage Practices in the South of West Siberia

Managing soil biodiversity by reduced or no tillage is an increasingly popular approach. Soil mycobiome in Siberian agroecosystems has been scarcely studied; little is known about its changes due to tillage. We studied mycobiome in Chernozem under natural steppe vegetation and cropped for wheat by conventional or no tillage in a long-term field trial in West Siberia, Russia, by using ITS2 rDNA gene marker (Illumina MiSeq sequencing). Half of the identified OTUs were Ascomycota with 82% of the total number of sequence reads and showing, like other phyla (Basidiomycota, Zygomycota, Mortierellomycota, Chytridiomycota, Glomeromycota), field-related differential abundance. Several dominant genera (Mortierella, Chaetomium, Clonostachys, Gibberella, Fusarium, and Hypocrea) had increased abundance in both cropped soils as compared with the undisturbed one and therefore can be safely assumed to be associated with wheat residues. Fungal OTUs' richness in cropped soils was less than in the undisturbed one; however, no tillage shifted soil mycobiome composition closer to the latter, albeit, it was still similar to the ploughed soil, despite different organic matter and wheat residue content. The study provided the first inventory of soil mycobiome under different tillage treatments in the south of West Siberia, where wheat production is an important section of the regional economy.

Hyphal Fusions Enable Efficient Nutrient Distribution in Colletotrichum graminicola Conidiation and Symptom Development on Maize

Hyphal and germling fusion is a common phenomenon in ascomycetous fungi. Due to the formed hyphal network, this process enables a coordinated development as well as an interaction with plant hosts and efficient nutrient distribution. Recently, our laboratory work demonstrated a positive correlation between germling fusion and the formation of penetrating hyphopodia on maize leaves outgoing from Colletotrichum graminicola oval conidia. To investigate the probable interconnectivity of these processes, we generated a deletion mutant in Cgso, in which homologs are essential for cellular fusion in other fungal species. However, hyphopodia development was not affected, indicating that both processes are not directly connected. Instead, we were able to link the cellular fusion defect in ∆Cgso to a decreased formation of asexual fruiting bodies of C. graminicola on the leaves. The monitoring of a fluorescent-labelled autophagy marker, eGFP-CgAtg8, revealed a high autophagy activity in the hyphae surrounding the acervuli. These results support the hypothesis that the efficient nutrient transport of degraded cellular material by hyphal fusions enables proper acervuli maturation and, therefore, symptom development on the leaves.