Journal Articles

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    Mapping QTL associated with resistance to Pseudomonas syringae pv. actinidiae in kiwifruit (Actinidia chinensis var. chinensis).
    (Frontiers Media S.A., 2024-03-26) Flay C; Symonds VV; Storey R; Davy M; Datson P; Hinrichsen P
    Pseudomonas syringae pv. actinidiae (Psa) is a bacterial pathogen of kiwifruit. This pathogen causes leaf-spotting, cane dieback, wilting, cankers (lesions), and in severe cases, plant death. Families of diploid A. chinensis seedlings grown in the field show a range of susceptibilities to the disease with up to 100% of seedlings in some families succumbing to Psa. But the effect of selection for field resistance to Psa on the alleles that remain in surviving seedlings has not been assessed. The objective of this work was to analyse, the effect of plant removal from Psa on the allele frequency of an incomplete-factorial-cross population. This population was founded using a range of genotypically distinct diploid A. chinensis var. chinensis parents to make 28 F1 families. However, because of the diversity of these families, low numbers of surviving individuals, and a lack of samples from dead individuals, standard QTL mapping approaches were unlikely to yield good results. Instead, a modified bulk segregant analysis (BSA) overcame these drawbacks while reducing the costs of sampling and sample processing, and the complexity of data analysis. Because the method was modified, part one of this work was used to determine the signal strength required for a QTL to be detected with BSA. Once QTL detection accuracy was known, part two of this work analysed the 28 families from the incomplete-factorial-cross population that had multiple individuals removed due to Psa infection. Each family was assigned to one of eight bulks based on a single parent that contributed to the families. DNA was extracted in bulk by grinding sampled leaf discs together before DNA extraction. Each sample bulk was compared against a bulk made up of WGS data from the parents contributing to the sample bulk. The deviation in allele frequency from the expected allele frequency within surviving populations using the modified BSA method was able to identify 11 QTLs for Psa that were present in at least two analyses. The identification of these Psa resistance QTL will enable marker development to selectively breed for resistance to Psa in future kiwifruit breeding programs.
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    Phenotypic properties and genotyping analysis of Bacillus cereus group isolates from dairy and potato products
    (Elsevier Ltd, 2021-04) Huang Y; Flint SH; Yu S; Ding Y; Palmer JS
    Bacillus cereus group (B. cereus sensu lato) are ubiquitously distributed in diverse environments. In this study, eight isolates including B. cereus, B. paranthracis and B. toyonensis species, from dairy and potato products, were assessed for biofilm formation, sporulation and genetic information including biofilm-related genes and toxin genes. The isolates varied in their ability to form biofilm (either at the stainless steel-liquid-air interface or floating pellicles). The amounts of biofilms of B. cereus s.l., were increased when incubated in agitation condition varied between isolates. Sporulation within the planktonic and biofilm modes of growth was compared, suggesting that biofilm is a favourable environment for B. cereus s.l. to form spores. Whole genome sequencing (WGS) was used to compare these B. cereus s.l. isolates. New sequence types (STs) of B. cereus were found in this study. Isolates that shared similar genomes had different biofilm-forming and sporulation abilities. Most of isolates tested, possessed biofilm-related genes. Different combinations of toxin-producing genes were identified in different isolates, with all isolates containing nhe while only some contained hbl and cytK. None of the food isolates contained the emetic ces gene. This study highlights the diversity of B. cereus s.l. in biofilm formation, sporulation and their genetic variables.