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ISHS Acta Horticulturae 264: II International Protea Research Symposium

EVALUATION OF THE RESISTANCE OF PINCUSHION (LEUCOSPERMUM SPP.) BREEDING LINES TO ROOT ROT CAUSED BY PHYTOPHTHORA CINNAMOMI

Authors:   S.L. von Broembsen, G.J. Brits
Abstract:
Phytophthora root rot is a limiting factor in the production of cut flower pincushions worldwide, but especially in South Africa. Investigations were initiated to identify root rot resistance within the genus Leucospermum that might be utilized for the development of resistant cultivars or rootstocks. Three different methods were used to assess the resistance of Leucospermum hybrids and species selections. Firstly, shoot cuttings were wound inoculated with P. cinnamomi mycelium under controlled, laboratory conditions. Lengths of lesions which developed from the inoculations were used to estimate relative resistance. This detached shoot assay proved too unreliable to be used for assessment. Secondly, one-year-old rooted cuttings were inoculated by applying zoospores of Phytophthora cinnamomi to the soil mix of individual pots in a trial conducted in a shade house. All of the lines tested were found to be susceptible to infection, but some lines were tolerant to infection. Thirdly, field evaluations of resistance were carried out for three years at a site with high natural inoculum levels and other soil factors favoring disease. Good levels of tolerance were observed for several hybrids and species selections. Useful differences in tolerance were also recorded among breeding lines within species. The most tolerant lines are being further evaluated.
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