Morphological and molecular identification of new records and new host plants of powdery mildews (Erysiphaceae) from Mexico

Powdery mildew is one of the most severe diseases affecting Cucurbitaceae. We identify the members of Erysiphaceae infecting cucurbits in three producing regions in Mexico. We determined that Golovinomyces ambrosiae, Neoerysiphe sechii, and Podosphaera xanthii infected cultivated and wild cucurbits species or subspecies. Leaf samples showing symptoms and signs of powdery mildew were collected from the northwestern, central western, and eastern regions of Mexico between 2017 and 2020. Species associated with the disease were identified based on morphology and ITS rDNA sequences. All powdery mildew specimens presented only the anamorph. Podosphaera xanthii was the predominant species; it was found in 85.7 % of the samples and in 13 out of 14 species or subspecies of cucurbits. Neoerysiphe sechii was found in 15.23 % of the samples and in only four cucurbit species from the central western and eastern regions of Mexico. Golovinomyces ambrosiae was documented for the first time in a Cucurbitaceae species (Sicyos deppei) from Central West Mexico. Three new hosts were registered for Neoerysiphe sechii (Cucurbita ficifolia, Echinopepon milleflorus, and Sicyos laciniatus) and eight for Podosphaera xanthii (Cucurbita argyrosperma, C. argyrosperma subsp. sororia, C. ficifolia, C. okeechobeensis subsp. martinezii, C. radicans, Sechium edule, Sicyos laciniatus, and S. deppei).

Discovery of a Cryptic Species, Erysiphe Salicina Sp. Nov., and Reconstruction of The Phylogeny of Powdery Mildews On Populus and Salix Spp.

Recently performed phylogenetic-taxonomic analyses of species belonging to Erysiphe sect. Uncinula on willows (Salix spp.) demonstrated a much higher diversity than previously assumed. Phylogenetic analyses and morphological examinations of Chinese Erysiphe collections on Salix abscondita (= S. raddeana), S. sinica and S. taraikensis, all belonging to Salix subgen. Vetrix sect. Vetrix, revealed an additional cryptic species in sister position to the E. salicis clade, which is described as Erysiphe salicina. The new species clearly distinguished from all allied species in morphological and genetical results. The phylogeny of the new species and closely related species on Populus and Salix spp. (Salicaceae) was reconstructed and discussed using a combined alignment of the internal transcribed spacer (ITS) regions and 28S rDNA sequences. The present phylogenetic analyses suggest that the recently described E. salicicola (on Salix gracilistyla in South Korea) has to be reduced to synonymy with E. salicis var. salicis-gracilistylae (º Uncinula salicis-gracilistylae).

SEVERITY AND INTENSITY OF FUNGAL DISEASES OF CUCURBIT CROPS OF HAMIRPUR REGION, HP, INDIA

Cucurbitaceae is the vegetable family enriched with numerous vitamins and minerals. In early rainy season cucurbits are the host of different fungal pathogens. In present study, four fungal diseases dominant on three members of cucurbitaceae family are observed in Bhoranj block of District Hamirpur, lie in lower foot hills of Himachal Pradesh. Four fungal diseases along with host plants are leaf spot of Lagenaria siceraria, downy mildews of Cucumis sativus, powdery mildews of Coccinia grandis and powdery mildews of Cucumis sativus. Among all these diseases, Disease Incidence and Disease Severity of Powdery mildews of Coccinia grandis are most dominant i.e. 40.3±1 and 51.2±1 respectively. Disease Incidence and Disease Severity of Leaf spot of Lagenaria siceraria is least i.e. 12.5±1 and 1.1±1, respectively.

EXTRA LARGE G-PROTEIN 2 (XLG2) mediates cell death and hyperimmunity via a novel, apoplastic ROS-independent pathway in Arabidopsis thaliana

Heterotrimeric G-Proteins are signal transduction complexes comprised of three subunits, Gα, Gβand Gγ, and are involved in many aspects of plant life. The non-canonical Gα subunit XLG2 mediates PAMP-induced ROS generation and immunity downstream of PRRs. A mutant of the chitin receptor component CERK1, cerk1-4, maintains normal chitin signalling capacity, but shows excessive cell death upon infection with powdery mildews. We identified XLG2 mutants as suppressors of the cerk1-4 phenotype. We generated stably transformed Arabidopsis lines expressing Venus-XLG2 and numerous mutated variants. These were analysed by confocal microscopy, Western blotting and pathogen infection. We also crossed cerk1-4 with several mutants involved in immunity and analysed their phenotype. Phosphorylation of XLG2 was investigated by quantitative proteomics. Mutations in XLG2 complex partners AGB1 and AGG1 have a partial cerk1-4 suppressor effect. The cerk1-4 phenotype is independent of NADPH oxidase-generated ROS, BAK1 and SOBIR1, but requires PUB2. XLG2 mediates cerk1-4 cell death at the cell periphery. Integrity of the XLG2 N-terminal domain, but not its phosphorylation, is essential for correct XLG2 localisation and cerk1-4 signalling. Our results suggest that XLG2 transduces signals from an unknown cell surface receptor that activates an apoplastic ROS-independent cell death pathway in Arabidopsis.

Strobilurins: New group of fungicides

Strobilurin is a group of natural products and their synthetic analogs have been widely used to control and prevent fungal diseases. Strobilurins were firstly isolated in 1977 from the mycelium of Strobilurus tenacellus, a saprobic Basidiomycete fungus causing wood-rotting on forest trees. This group of pesticides was designed to manage fungal pathogens classes such as Ascomycetes, Basidiomycetes, and Oomycetes. Also, Strobilurin commercialized included derivatives such as are azoxystrobin, kresoxim-methyl, picoxystrobin, fluoxastrobin, oryzastrobin, dimoxystrobin, pyraclostrobin and trifloxystrobin. This group is a part of the larger group of QoI inhibitors, which act to inhibit the respiratory chain at the level of Complex III. Strobilurins group control an unusually wide array of fungal diseases, included water molds, downy mildews, powdery mildews, leaf spotting and rusts. This group are used on cereals, field crops, fruits, tree nuts, vegetables, turfgrasses and ornamentals. Also, Strobilurins found to enhance the plant growth in some cases.

The mitochondrial genome of the grape powdery mildew pathogen Erysiphe necator is intron rich and exhibits a distinct gene organization

Powdery mildews are notorious fungal plant pathogens but only limited information exists on their genomes. Here we present the mitochondrial genome of the grape powdery mildew fungus Erysiphe necator and a high-quality mitochondrial gene annotation generated through cloning and Sanger sequencing of full-length cDNA clones. The E. necator mitochondrial genome consists of a circular DNA sequence of 188,577 bp that harbors a core set of 14 protein-coding genes that are typically present in fungal mitochondrial genomes, along with genes encoding the small and large ribosomal subunits, a ribosomal protein S3, and 25 mitochondrial-encoded transfer RNAs (mt-tRNAs). Interestingly, it also exhibits a distinct gene organization with atypical bicistronic-like expression of the nad4L/nad5 and atp6/nad3 gene pairs, and contains a large number of 70 introns, making it one of the richest in introns mitochondrial genomes among fungi. Sixty-four intronic ORFs were also found, most of which encoded homing endonucleases of the LAGLIDADG or GIY-YIG families. Further comparative analysis of five E. necator isolates revealed 203 polymorphic sites, but only five were located within exons of the core mitochondrial genes. These results provide insights into the organization of mitochondrial genomes of powdery mildews and represent valuable resources for population genetic and evolutionary studies.

Blumeria graminis (powdery mildew of grasses and cereals).

Powdery mildew is one of the most common and destructive diseases of cereals. Actual losses depend on the time of disease epidemic onset and its severity, and can at the extreme reach up to 60% (James et al., 1991; Oerke et al., 1994). Although it occurs in most, if not all, parts of the world where cereals are grown, powdery mildew is not considered to be a major problem in every region. This disease can be very destructive, but generally seems to cause most damage in temperate latitudes, especially in the northern hemisphere, where wheat and barley are more frequently cultivated (see map in Cowger et al., 2012). However, powdery mildew can also be a limiting factor for cereal production in subtropical and tropical areas. Yield losses by powdery mildews are generally complex to estimate and depend on several factors such as climate, year, cropping system, cereal species and cultivar.

Blumeria graminis (powdery mildew of grasses and cereals).

Powdery mildew is one of the most common and destructive diseases of cereals. Actual losses depend on the time of disease epidemic onset and its severity, and can at the extreme reach up to 60% (James et al., 1991; Oerke et al., 1994). Although it occurs in most, if not all, parts of the world where cereals are grown, powdery mildew is not considered to be a major problem in every region. This disease can be very destructive, but generally seems to cause most damage in temperate latitudes, especially in the northern hemisphere, where wheat and barley are more frequently cultivated (see map in Cowger et al., 2012). However, powdery mildew can also be a limiting factor for cereal production in subtropical and tropical areas. Yield losses by powdery mildews are generally complex to estimate and depend on several factors such as climate, year, cropping system, cereal species and cultivar.