Powdery mildew fungi (Erysiphales, Ascomycota) of Western Polissya of Ukraine

Information on powdery mildew fungi (Erysiphales, Ascomycota) recorded in Western Polissya of Ukraine throughout the history of research in the region is provided. The list included in the article comprises 85 species of 7 genera of Erysiphales, namely 43 species of Erysiphe, 19 of Golovinomyces, 15 of Podosphaera, three of Phyllactinia, two of Neoerysiphe and Sawadaea, and one species of Blumeria. For the first time, 21 species are reported for the region: Erysiphe astragali, E. azaleae, E. howeana, E. hypophylla, E. lycopsidis, E. macleayae, E. prunastri, E. russellii, E. syringae-japonicae, Golovinomyces ambrosiae, G. asterum, G. bolayi, G. fisheri, G. riedlianus, G. verbasci, Neoerysiphe galii, Phyllactinia fraxini, Podosphaera aucupariae, P. phtheirospermi, P. prunicola, and Sawadaea tulasnei. The most common species were Blumeria graminis, Erysiphe alphithoides, E. aquilegiae, E. divaricata, E. ornata, E. polygoni, Podosphaera aphanis, and P. myrtillina. Erysiphe heraclei, Neoerysiphe galeopsidis, and Podosphaera erigerontis-canadensis were recorded quite frequently. Erysiphe arcuata, E. astragali, E. azaleae, E. baeumleri, E. circaeae, E. cruchetiana, E. cruciferarum, E. grosulariae, E. hypophylla, E. lythri, E. macleayae, E. palczewskii, E. penicillata, E. pisi, E. prunastri, E. russellii, E. vanbruntiana, Golovinomyces ambrosiae, G. asterum, G. circumfusus, G. cynoglossi, G. fisheri, G. inulae, G. riedlianus, G. verbasci, Neoerysiphe galii, Phyllactinia fraxini, Ph. guttata s.str., Podosphaera amelanchieris, P. aucupariae, P. balsaminae, P. macularis, P. mors-uvae, P. prunicola, and Sawadaea tulasnei are known from one or two localities, so they are considered as rare species in Western Polissya of Ukraine.

Silencing of a Wheat Ortholog of Glucan Synthase-Like Gene Reduced Resistance to Blumeria graminis f. sp. tritici

Wheat powdery mildew, caused by the obligate biotrophic ascomycete fungal pathogen Blumeria graminis f. sp. tritici (Bgt), is a major threat to wheat production worldwide. It is known that Arabidopsis thaliana glucan synthase-like 5 (AtGSL5) improves the resistance of wheat to powdery mildew by increasing its anti-penetration abilities. However, the function of glucan synthase-like (GSL) orthologs in crop species remains largely unknown. In this study, TaGSL22, a novel functional ortholog of AtGSL5, was isolated as the only Bgt-induced GSL gene in wheat. Phylogenetic analysis indicated that TaGSL22 was conserved within the group of Gramineae and showed a closer relationship to GSL orthologs from monocots than to those from dicots. The TaGSL22 transcript was highest in the wheat leaves, followed by stems then roots. TaGSL22 was localized in the cell membrane and cytoplasm of wheat protoplasts, as predicted by transmembrane structure analysis. In addition, expression of TaGSL22 was induced by the plant hormones ethylene (ETH) and salicylic acid (SA), but down-regulated by jasmonate (JA) and abscisic acid (ABA). The transcript level of TaGSL22 was up-regulated in the incompatible interaction between Bgt and wheat, whereas it remained relatively unchanged in the compatible interaction. Knocking down of TaGSL22 by virus-induced gene silencing (VIGS) induced a higher infection type in the wheat–Bgt interaction. The TaGSL22-silenced plants exhibited reduced resistance to Bgt, accompanied by decreased callose accumulation. Our study shows a conserved function of GSL genes in plant immunity associated with penetration resistance, and it indicates that TaGSL22 can be used to improve papilla composition and enhance resistance to wheat powdery mildew.

Detection of spring wheat plants affected by powdery mildew using hyperspectral survey data

In laboratory experiments, spectral characteristics of three varieties of Siberian selection spring wheat affected under field conditions by powdery mildew (Blumeria graminis (DC.) Speer) were obtained using hyperspectral camera. The variety specificity of the reflectivity of wheat leaves affected by powdery mildew with the same severity has been established. A change in the leaves reflectivity depending on the severity was revealed. The most informative spectral indicator (index) for the powdery mildew detection has been determined.

First Report of Powdery Mildew Caused by Blumeria graminis on Poa pratensis var. anceps Gaud cv. Qinghai in China

Poa pratensis, an important cool-season perennial grass, is widely cultivated for construction of grasslands and ecological management of Qinghai-Tibet Plateau (Dong et al. 2020). Poa pratensis var. anceps Gaud cv. Qinghai (PPAQ) is a variant of P. pratensis (Liu et al. 2009). In June 2016, powdery mildew was observed on PPAQ in an artificial field of PPAQ in Haiyan county of Haibei Tibetan Autonomous Prefecture, Qinghai province, China (36°59′17.76″N, 100°52′54.01″E). Approximately 30 to 50% of leaves (approximate 10 ha) were affected. Initially, irregular white mycelial colonies were observed on the adaxial surface of affected leaves. The colonies increased in number and size, and later covered a large area of leaves and stems. In advanced stages of disease, the colonies covered the whole adaxial surface and white patches appeared on the abaxial surface of affected leaves, and eventually caused leaf death. Conidiophores were unbranched, measuring 160 to 235 × 4 to 13 μm, and borne vertically on hyphae. Each conidiophore produced 4 to 11 conidia in a chain. The conidia were oval, one-celled, and hyaline, measuring 22 to 40 ×10 to 21 μm (n = 50). Chasmothecia were yellow, spherical, and 172 to 240 μm in diameter (n = 20), each of which contained 8 to 17 asci. The appendages were few, and hyphoid. Asci were oblong or ovate, measuring 79 to 115 × 31 to 45 μm (n = 20). Asci were petiolate, containing eight ascospores. Ascospores were round to oval, colorless, one-celled, measuring 17 to 33 × 8 to 14 μm (n = 50). Based on morphological characteristics, the fungal organism was identified as Blumeria graminis (DC.) Speer. To confirm the identification, the internal transcribed spacer (ITS) of 612 bp was amplified from DNA of conidia using ITS5 and P3 primers (Takamatsu et al. 2009). The ITS sequence was deposited in GenBank database (Accession No. MF429949). The ITS showed 95% sequence similarity with those of B. graminis on Poa nemoralis in USA (Accession No. AB273560) and on P. bullbosa in Iran (Accession No. AB273551) (Inuma et al. 2007). Five two-month-old healthy plants were inoculated by spraying a spore suspension (1× 105 conidia ml-1) prepared from conidia brushed from infected plants; five plants sprayed with sterile distilled water served as controls. All the plants were maintained in a growth chamber with a constant temperature of 20°C, a 12 h/12 h light/dark diurnal cycle, and 70% humidity. Two weeks after inoculation, symptoms of powdery mildew were observed on all inoculated plants, whereas the control plants remained symptomless. The same fungus was confirmed by morphological characterization and molecular assays as described above. B. graminis has been reported on P. pratensis in USA (Dugan and Newcombe 2007), Israel (Voytyuk et al. 2009), and China (Zhang et al. 2014), but has not previously been reported on PPAQ. As far as we know, this is the first report of powdery mildew caused by B. graminis on PPAQ in China. These findings indicated that the health of PPAQ was substantially threaten when infected by powdery mildew, therefore, our results also contributed some valuable information how to diagnose this disease on PPAQ in China.

New Pathotype Nomenclature for Better Characterisation the Virulence and Diversity of Blumeria graminis f.sp. avenae Populations

Fungal cereal pathogens, including Blumeria graminis f.sp. avenae, have the ability to adapt to specific conditions, which in turn leads to overcoming host resistance. An important aspect is the standardized way of characterizing the races and pathotypes of the pathogen. In the presented work, for the first time it was proposed to use a unified letter code that allows describing the pathotypes of B. graminis f.sp. avenae. The set of 14 oat genotypes were used as a differential set. This set included genotypes having so far described powdery mildew resistance genes Pm1–Pm11, and two genotypes (A. sterilis and A. strigosa) with effective sources of resistance to Bga. Based on the analysis of 160 Bga isolates collected in 2016–2019 from 4 locations in Poland, the most numerous was the TBBB pathotype, represented by 30% of the tested isolates. It was present in all analyzed populations. Subsequently, 8.1% and 6.3% of the isolates represented the TBCB and RBBB pathotypes, respectively.

RACE1, a Japanese Blumeria graminis f. sp. hordei isolate, is capable of overcoming partially mlo-mediated penetration resistance in barley in an allele-specific manner

Loss-of-function mutation of the MILDEW RESISTANCE LOCUS O (Mlo) gene confers durable and broad-spectrum resistance to powdery mildew fungi in various plants, including barley. In combination with the intracellular nucleotide-binding domain and leucine-rich repeat receptor (NLR) genes, which confer the race-specific resistance, the mlo alleles have long been used in barley breeding as genetic resources that confer robust non-race-specific resistance. However, a Japanese Blumeria graminis f. sp. hordei isolate, RACE1, has been reported to have the potential to overcome partially the mlo-mediated penetration resistance, although this is yet uncertain because the putative effects of NLR genes in the tested accessions have not been ruled out. In this study, we examined the reproducibility of the earlier report and found that the infectious ability of RACE1, which partially overcomes the mlo-mediated resistance, is only exerted in the absence of NLR genes recognizing RACE1. Furthermore, using the transient-induced gene silencing technique, we demonstrated that RACE1 can partially overcome the resistance in the host cells with suppressed MLO expression but not in plants possessing the null mutant allele mlo-5.

Mlo Resistance to Powdery Mildew (Blumeria graminis f. sp. hordei) in Barley Landraces Collected in Yemen

Barley (Hordeumvulgare L.) is one of the most important cereal crops in the world. Powdery mildew on barley, which is caused by the pathogen Blumeria graminis f. sp. hordei, occurs world-wide and can result in severe yield loss. Thousands of barley accessions are stored in national gene banks, and their characterization for breeding purposes is needed. This study was conducted to determine the resistance to powdery mildew in 33 barley landraces from Yemen, which were obtained from the ICARDA gene bank. Twenty differential isolates of barley powdery mildew were used. Nine single plant lines were selected from five landraces, based on tests that were performed with 30 plants per landrace, after inoculation with the most avirulent isolate of barley powdery mildew available. Two of these landraces originated from the Al Bayda province in Yemen, and three others originated from Dhamar, Sanaa, and Taizz, respectively. Next, single plant lines were tested using a set of 20 differential isolates of powdery mildew. Two lines that were selected from landrace from the Al Bayda province in Yemen, showed disease reaction designated as 0(4), which is specific for the presence of Mlo resistance. The new source of highly effective Mlo powdery mildew resistance that is described in this study could be used in barley breeding programs.