Using a Hybrid Mapping Population to Identify Genomic Regions of Pyrenophora teres Associated With Virulence

Net blotches caused by Pyrenophora teres are important foliar fungal diseases of barley and result in significant yield losses of up to 40%. The two types of net blotch, net-form net blotch and spot-form net blotch, are caused by P. teres f. teres (Ptt) and P. teres f. maculata (Ptm), respectively. This study is the first to use a cross between Ptt and Ptm to identify quantitative trait loci (QTL) associated with virulence and leaf symptoms. A genetic map consisting of 1,965 Diversity Arrays Technology (DArT) markers was constructed using 351 progenies of the Ptt/Ptm cross. Eight barley cultivars showing differential reactions to the parental isolates were used to phenotype the hybrid progeny isolates. Five QTL associated with virulence and four QTL associated with leaf symptoms were identified across five linkage groups. Phenotypic variation explained by these QTL ranged from 6 to 16%. Further phenotyping of selected progeny isolates on 12 more barley cultivars revealed that three progeny isolates are moderately to highly virulent across these cultivars. The results of this study suggest that accumulation of QTL in hybrid isolates can result in enhanced virulence

Re-visiting management options for charcoal rot in sorghum [eXtension AUS Field Crop Diseases, 19 March 2018 - Online community]

With the summer cropping season nearing completion, growers are hoping for an above average yield of sorghum crop for the 2017/2018 summer growing season in the Northern Region. Crops looked good as of the end of January (Figure 1), but by mid-February tweets were flying and phone calls were being received by USQ’s Centre for Crop Health about increasing lodging in crops (Figures 2-3)

Summer paddock survey finds fungal and bacterial diseases decreased but not eliminated [GRDC Field Crop Diseases Community of Practice, 1 October 2018 - Online community]

Summer crop paddocks across northern New South Wales, southern Queensland and central Queensland, were surveyed to monitor the fungal and bacterial diseases present in the 2017-2018 summer cropping season. The season was unusually hot and dry, which in most cases, led to reduced fungal and bacterial diseases, but did not eliminate all of them. In some cases, these conditions actually favoured the development of disease, for example charcoal rot in sorghum. Observations for maize, mungbean, peanut, sorghum, soybean and sun]ower are given below

Whole genome data from Curtobacterium flaccumfaciens pv. flaccumfaciens strains associated with tan spot of mungbean and soybean reveal diverse plasmid profiles

Despite the substantial economic impact of Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff) on legume productions worldwide, the genetic basis of its pathogenicity and potential host association is poorly understood. The production of high-quality reference genome assemblies of Cff strains associated with different hosts sheds light on the genetic basis of its pathogenic variability and host association. Moreover, the study of recent outbreaks of bacterial wilt and microevolution of the pathogen in Australia requires access to high-quality, reference genomes that are sufficiently closely related to the population being studied within Australia. We provide the first genome assemblies of Cff strains associated with mungbean and soybean, which revealed high variability in their plasmid composition. The analysis of Cff genomes revealed an extensive suite of carbohydrate-active enzymes potentially associated with pathogenicity, including four carbohydrate esterases, 50 glycoside hydrolases, 23 glycosyl transferases, and a polysaccharide lyase. We also identified 11 serine peptidases, three of which were located within a linear plasmid, pCff119. These high-quality assemblies and annotations will provide a foundation for population genomics studies of Cff in Australia and for answering fundamental questions regarding pathogenicity factors and adaptation of Cff to various hosts worldwide, and, at a broader scale, contribute to unravelling genomic features of Gram-positive, xylem-inhabiting bacterial pathogens

Genetic structure of Cercospora beticola populations on Beta vulgaris in New York and Hawaii

Cercospora leaf spot (CLS), caused by Cercospora beticola, is a major disease of Beta vulgaris worldwide. No sexual stage is known for C. beticola but in its asexual form it overwinters on infected plant debris as pseudostromata, and travels short distances by rain splash-dispersed conidiospores. Cercospora beticola infects a broad range of host species and may be seedborne. The relative contribution of these inoculum sources to CLS epidemics on table beet is not well understood. Pathogen isolates collected from table beet, Swiss chard and common lambsquarters in mixed-cropping farms and monoculture fields in New York and Hawaii, USA, were genotyped (n = 600) using 12 microsatellite markers. All isolates from CLS symptoms on lambsquarters were identified as C. chenopodii. Sympatric populations of C. beticola derived from Swiss chard and table beet were not genetically differentiated. Results suggested that local (within field) inoculum sources may be responsible for the initiation of CLS epidemics in mixed-cropping farms, whereas external sources of inoculum may be contributing to CLS epidemics in the monoculture fields in New York. New multiplex PCR assays were developed for mating-type determination for C. beticola. Implications of these findings for disease management are discussed

A novel pathogenesis-related protein (LcPR4a) from lentil, and its involvement in defence against Ascochyta lentis

A novel pathogenesis-related protein 4 (PR4) encoding gene, LcPR4a, was induced in Lens culinaris following Ascochyta lentis infection. LcPR4a encodes a predicted 146 amino acid protein of 15.8 kDa. The putative LcPR4a protein belongs to the class II PR4 family and has close phylogenetic affinity to PR4 proteins from related species. qPCR analysis revealed differential expression of the LcPR4a gene upon Ascochyta lentis infection in both resistant and susceptible cultivars. This, combined with preliminary in vitro antifungal assays of the recombinant protein expressed in E. coli, suggests the potential important role of LcPR4a in the defence response of lentil to Ascochyta lentis attack

IMA Genome - F16 – Draft genome assemblies of Fusarium marasasianum, Huntiella abstrusa, two Immersiporthe knoxdaviesiana isolates, Macrophomina pseudophaseolina, Macrophomina phaseolina, Naganishia randhawae, and Pseudocercospora cruenta

Draft genome assembly of Fusarium marasasianum Introduction Many plants are thought to have at least one Fusarium-associated disease with more than 80% of economically important plants affected by at least one Fusarium disease (Leslie and Summerell 2006). The socioeconomic importance of Fusarium is particularly evident when considering the Fusarium fujikuroi species complex (FFSC, sensu Geiser et al. 2021). This monophyletic group contains 65 species and numerous cryptic species (Yilmaz et al. 2021). More than 50 species in the FFSC have publicly available genomes (www.ncbi.nlm.nih.gov), indicative of their economic importance. A number of recent studies showed that the FFSC complex contains four large clades (Herron et al. 2015; Sandoval-Denis et al. 2018; Yilmaz et al. 2021). One of these corresponds to the so-called “American” clade that was initially proposed to reflect the biogeography of the species it contains (O’Donnell et al. 1998). For example, Fusarium circinatum, the pine pitch canker pathogen, is thought to be native to Mexico and Central America (Drenkhan et al. 2020), where it likely co-evolved with its Pinus hosts (Herron et al. 2015; O’Donnell et al. 1998; Wikler and Gordon 2000). The American clade also includes five additional species associated with Pinus species in Colombia. These species are F. fracticaudum, F. pininemorale, F. parvisorum, F. marasasianum, and F. sororula, of which F. parvisorum, F. marasasianum, and F. sororula displayed levels of pathogenicity that were comparable to those of F. circinatum on susceptible Pinus species (Herron et al. 2015). The risk that the various American clade species pose to forestry in Colombia and globally has provided the impetus for projects aiming to sequence their genomes. To complement the genomic resources available for F. circinatum (Fulton et al. 2020; van der Nest et al. 2014a; Van Wyk et al. 2018; Wingfield et al. 2012, 2018a), the genomes of F. pininemorale (Wingfield et al. 2017), F. fracticaudum (Wingfield et al. 2018b) and F. sororula (van der Nest et al. 2021) have been published. Here we present the whole genome sequence for the pine pathogen F. marasasianum, named after the late South African professor Walter “Wally” F.O. Marasas (Wingfield and Crous 2012) who specialised in the taxonomy of Fusarium species and their associated mycotoxins

Australia: A Continent Without Native Powdery Mildews? The First Comprehensive Catalog Indicates Recent Introductions and Multiple Host Range Expansion Events, and Leads to the Re-discovery of Salmonomyces as a New Lineage of the Erysiphales

In contrast to Eurasia and North America, powdery mildews (Ascomycota, Erysiphales) are understudied in Australia. There are over 900 species known globally, with fewer than currently 60 recorded from Australia. Some of the Australian records are doubtful as the identifications were presumptive, being based on host plant-pathogen lists from overseas. The goal of this study was to provide the first comprehensive catalog of all powdery mildew species present in Australia. The project resulted in (i) an up-to-date list of all the taxa that have been identified in Australia based on published DNA barcode sequences prior to this study; (ii) the precise identification of 117 specimens freshly collected from across the country; and (iii) the precise identification of 30 herbarium specimens collected between 1975 and 2013. This study confirmed 42 species representing 10 genera, including two genera and 13 species recorded for the first time in Australia. In Eurasia and North America, the number of powdery mildew species is much higher. Phylogenetic analyses of powdery mildews collected from Acalypha spp. resulted in the transfer of Erysiphe acalyphae to Salmonomyces, a resurrected genus. Salmonomyces acalyphae comb. nov. represents a newly discovered lineage of the Erysiphales. Another taxonomic change is the transfer of Oidium ixodiae to Golovinomyces. Powdery mildew infections have been confirmed on 13 native Australian plant species in the genera Acacia, Acalypha, Cephalotus, Convolvulus, Eucalyptus, Hardenbergia, Ixodia, Jagera, Senecio, and Trema. Most of the causal agents were polyphagous species that infect many other host plants both overseas and in Australia. All powdery mildews infecting native plants in Australia were phylogenetically closely related to species known overseas. The data indicate that Australia is a continent without native powdery mildews, and most, if not all, species have been introduced since the European colonization of the continent