Testing of selected South African Pinus hybrids and families for tolerance to the pitch canker pathogen, Fusarium circinatum
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Plantations of Pinus spp. constitute approximately 50% of the South African forestry industry. The first aim of this study was to develop a reliable inoculation technique to screen Pinus spp., for tolerance to infection by F. circinatum, which threatens pine forestry in South Africa. Inoculation of branches was compared with stem inoculations and we considered the number of branches or trees required to obtain statistically significant results. Furthermore, variation in the susceptibility of some Pinus families, clones and hybrids was considered. Results showed that branch inoculations were closely correlated with those from stem inoculations, and that it is important to consider branch and stem diameters when assessing susceptibility of trees. Subsequent trials using branch inoculations showed significant differences in F. circinatum tolerance amongst a range of pine species and hybrids of potential interest to forestry in South Africa. Significant differences in susceptibility were also found among clones of two P. radiata families. The most tolerant trees were P. elliottii × caribaea and P. patula × oocarpa hybrids, while the most susceptible species were P. patula, P. greggii and hybrids of these two. This is the first trial considering the susceptibility of Pinus hybrids, Pinus clones and some P. patula provenances, and the results indicate excellent potential for breeding for tolerance to pitch canker in South Africa.
Application The accurate selection of disease tolerant planting stock for the South African forestry industry is crucially important for the continued sustainability of this important industry. The work described here provides valuable information on an artificial inoculation technique that will assist the industry in screening trees for tolerance to the pitch canker fungus, F. circinatum. It also provides some indication of the relative susceptibility of a number of Pinus spp., hybrids and families currently being evaluated in the country.
KeywordsForestry Fungal disease Inoculation Resistance Screening
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We thank the members of the Tree Protection Co-operative Programme (TPCP), the National Research Foundation and the THRIP initiative of the Department of Trade and Industry (DTI) for financial support. The staff of SAFCOL and particularly Jacob Matroos, Pearl Oelf and Cecilia Bester are acknowledged for production of the cuttings, planting and maintenance of the trials used to develop the inoculation technique. Staff of Mondi Business Paper and Sappi Forests and particularly Andre van der Hoef and Noel Myburg are thanked for providing trees for inoculation. Students belonging to the TPCP team, University of Pretoria, are gratefully acknowledged for volunteering assistance with large numbers of inoculations and with the enumeration of results. Henriette Britz van Heerden is also thanked for selection of the isolate used in the inoculation studies.
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