Research Highlights

2014

  • First report of D. pini on P. radiata
    • Piou and Ioos 2014. Plant Disease.
    • France
  • Four new host records and first report of Dothistroma needle blight caused by Dothistroma pini in North and South Dakota, and in Indiana in the U.S.A.
    • Barnes et al. 2014. Plant Disease 98: 1443.
    • Pinus nigra, P. flexilis, P. ponderosa, P. cembra and P. albicaulis
  • Global population structure and diversity in an invasive pine needle pathogen reflects anthropogenic activity.
    • Barnes et al. 2014. Ecology and Evolution DOI:10.1002/ece3.1200.
    • 458 isolates of D. septosporum from 14 countries on six continents using microsatellite markers.
    • Northern Hemisphere:
      • High genetic diversities
      • Both mating types
      • Europe:
        • Most populations showed evidence for random mating
        • Little population differentiation
        • Gene flow between countries.
        • North America (USA) and Asia (Bhutan):
          • Genetically distinct but migration between these continents and Europe was evident.
    • Southern Hemisphere:
      • Population structure and diversity of reflected the anthropogenic history of the introduction and establishment of plantation forestry, particularly with Pinus radiata.
      • Three introductory lineages in the Southern Hemisphere were observed.
      • Africa:
        • Longest history of pine introductions.
        • Greatest diversity, indicating multiple introductions.
        • South America and Australasia:
          • More recent introductions have occurred separately.
          • Only one mating type – clonal.
  • Dothistromin toxin is a virulence factor in dothistroma needle blight of pines
    • Kabir et al. 2014. Plant Pathology.
    • Pinus radiata infected with dothistromin-deficient mutants of D. septosporum.
    • The mutants were able to infect pine needles and complete their life cycle as previously shown, and were unaffected in spore germination, epiphytic growth or needle penetration.
    • However, colonization of the mesophyll by the mutants was restricted compared to the wild type.
    • Lesions produced by the mutants were smaller and produced significantly fewer spores than lesions produced by wildtype strains.
    • ‘Green islands’, in which chlorophyll was maintained at a higher level than in adjacent chlorotic and necrotic regions, surrounded early-appearing lesions caused by both wildtype and mutant strains. At a later stage of disease development green islands were still present in the mutant but appeared to be masked by the extended dothistromin-containing lesions in the wild type.
    • Overall the results support a role for dothistromin in virulence in dothistroma needle blight.
  • The hemibiotrophic lifestyle of the fungal pine pathogen Dothistroma septosporum
    • Kabir et al. 2014. Forest Pathology.
    • Biotrophic-type phase in which the fungus grew over the needle surface, penetrated through stomatal pores and colonised epistomatal chambers. S
    • Subsequent necrotrophic phase was characterised by colonisation of the mesophyll and production of dothistromin, with a >100-fold increase in dothistromin levels from early necrotic lesion to sporulating lesion stages.
    • This is consistent with the role of dothistromin as a virulence factor that is involved in lesion expansion.
  • Native Scottish Pinus sylvestris populations vary in susceptibility to DNB
    • Fraser et al. 2014. Plant Pathology.
    • Artificial inoculations
    • 6 native/natural P. sylvestris populations vary in susceptibility
    • Under optimum conditions for DNB, inoculum load affects DNB severity but has no impact on the relative susceptibilities of P. sylvestris populations
  • DNB in Switzerland is caused by both D. pini and D. septosporum
    • Queloz et al. 2014. Plant Disease.
  • Increased August minimum temp. and increases in precipitation linked to DNB outbreaks in BC, Canada
    • Welsh et al. Canadian Journal of Forest Research 44, 212–219.
    • Trend towards increased August minimum temperatures appears to be an important climate factor contributing to the spread of the disease.
    • Graphical comparisons of total April precipitation reveal that periods of above-average precipitation coincided with periods of outbreak increase.
    • Decreases in August minimum temperature also correspond to decreases in outbreak severity.
    • Spike in spring precipitation associated with the current epidemic.
    • The extent and severity of the current disease epidemic raises the possibility that the key factors that drive outbreaks have become more frequent, enabling the emergence of DNB as a serious disease.