Epidemic spread of smut fungi (Quambalaria) by sexual reproduction in a native pathosystem

Quambalaria are fungal pathogens of Corymbia, Eucalyptus and related genera of Myrtaceae. They are smut fungi (Ustilaginomycota) described from structures that resemble conidia and conidiophores. Whether these spore forms have asexual or sexual roles in life cycles of Quambalaria is unknown. An epidemic of Q. pitereka destroyed plantations of Corymbia in New South Wales and Queensland (Australia) in 2008. We sampled 177 individuals from three plantations of C. variegata and used AFLPs to test hypotheses that the epidemic was spread by asexual reproduction and dominated by a single genotype. There was high genotypic diversity across ≥600 AFLP loci in the pathogen populations at each plantation, and evidence of sexual reproduction based on neighbour-net analyses and rejection of linkage disequilibrium. The populations were not structured by host or location. Our data did not support a hypothesis of asexual reproduction but instead that Q. pitereka spreads exclusively by sexual reproduction, similar to life cycles of other smut fungi. Epidemics were exacerbated by monocultures of Corymbia established from seed collected from a single provenance. This study showcases an example of an endemic pathogen, Q. pitereka, with a strictly outbreeding life cycle that has caused epidemics when susceptible hosts were planted in large monoculture plantations

Molecular diagnostics of banana Fusarium wilt targeting Secreted-in-Xylem genes

Fusarium wilt is currently spreading in banana growing regions around the world leading to substantial losses. The disease is caused by the fungus Fusarium oxysporum f. sp. cubense (Foc), which is further classified into distinct races according to the banana varieties that they infect. Cavendish banana is resistant to Foc race 1, to which the popular Gros Michel variety succumbed last century. Cavendish effectively saved the banana industry, and became the most cultivated commercial variety worldwide. However, Foc tropical race 4 (TR4) subsequently emerged in Southeast Asia, causing significant yield losses due to its high level of aggressiveness to Cavendish and other commonly grown varieties. Preventing further spread is crucially important in the absence of effective control methods or resistant market-acceptable banana varieties. Implementation of quarantine and containment measures depends on early detection of the pathogen through reliable diagnostics. In this study, we tested the hypothesis that secreted in xylem (SIX) genes, which currently comprise the only known family of effectors in F. oxysporum, contain polymorphisms to allow the design of molecular diagnostic assays that distinguish races and relevant VCGs of Foc. We present specific and reproducible diagnostic assays based on conventional PCR targeting SIX genes, using as templates DNA extracted from pure Foc cultures. Sets of primers specifically amplify regions of: SIX6 in Foc race 1, SIX1 gene in TR4, SIX8 in subtropical race 4, SIX9/SIX10 in Foc VCG 0121, and SIX13 in Foc VCG 0122. These assays include simplex and duplex PCRs, with additional restriction digestion steps applied to amplification products of genes SIX1 and SIX13. Assay validations were conducted to a high international standard including the use of 250 Fusarium spp. isolates representing 16 distinct Fusarium species, 59 isolates of F. oxysporum, and 21 different vegetative compatibility groups (VCGs). Tested parameters included inter and intraspecific analytical specificity, sensitivity, robustness, repeatability and reproducibility. The resulting suite of assays is able to reliably and accurately detect R1, STR4, TR4 as well as two VCGs (0121 and 0122) causing Fusarium wilt in bananas

Diagnostics of banana blood disease

Blood disease in bananas caused by Ralstonia syzygii subsp. celebesensis is a bacterial wilt disease that causes major yield losses of banana in Indonesia and peninsular Malaysia. The disease has significantly increased its geographic distribution in the past decade. Diagnostic methods are an important component of disease management in vegetatively propagated crops such as banana to constrain incursions of plant pathogens. Therefore, the objectives of this study were (i) to design and rigorously validate a novel banana Blood disease (BBD) real-time PCR assay with a high level of specificity and sensitivity of detection and (ii) to validate published PCR-based diagnostic methods targeting the intergenic region in the megaplasmid (“121 assay” with primer set 121) or the phage tail protein-coding sequence in the bacterial chromosome (“Kubota assay” and “BDB2400 assay” with primer set BDB2400). Assay validation included 339 samples (174 Blood disease bacteria, 51 bacteria associated with banana plants, 51 members of the Ralstonia solanacearum species complex, and 63 samples from symptomatic and healthy plant material). Validation parameters were analytical specificity (inclusivity and exclusivity), selectivity, limit of detection, accuracy, and ruggedness. The 121 assay and our newly developed BBD real-time PCR assay detected all R. syzygii subsp. celebesensis strains with no cross-specificity during validation. Two different PCR assays using the primer set BDB2400 lacked specificity and selectivity. This study reveals that our novel BBD real-time PCR assay and the conventional PCR 121 assay are reliable methods for Blood disease diagnostics, as they comply with all tested validation parameters

Effect of Antiplatelet Therapy on Survival and Organ Support–Free Days in Critically Ill Patients With COVID-19

International audienc