Two methods for sampling roots of comparable age were devised and used in separate experiments to investigate micro-organisms associated with white clover (Trifolillm repensL.) roots in pastures grazed by sheep at a lowland and a hill country site. Growth and microbial colonisation of young roots during winter and spring were studied by sampling successively from clover stolon nodes marked in autumn at the time of initiation of new roots. Also, a comparison was made between colonisation of #x2018;young#x2019; and #x2018;old#x2019; roots at the two sites in autumn and summer. Root invasion by micro-organisms, determined by both direct (microsopy) and indirect (plate culture isolation) methods, was found to be more frequent in old roots than young, at all sampling times and at both sites.Bimuria novae-zelandiaeD. Hawksw., Chea amp; Sheridan,Codinaea fertilisHughes amp; Kendrick,Fusarium oxysporumSchlecht., and sterile dark mycelial strains were the fungi most frequently isolated from root samples;C. fertilisandF. oxysporumwere more frequently isolated from lowland than hill country samples. Mycorrhizal fungi, organisms producing sporangia and cystosori within epidermal cells, and nematodes were consistently seen within young roots and are concluded to be primary invaders of white clover roots. Little root damage which could be attributed to fungal pathogens was detected during the investigation.
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