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Tolerance of Pinus patula hybrids to novel Fusarium circinatum haplotypes from Guatemala and Nicaragua

Irene Barnes: Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria

<div>Pitch canker, caused by <em>Fusarium circinatum,</em> is one of the most devastating diseases affecting commercial pine forestry, especially in the Southern Hemisphere. A pathogen survey conducted in Guatemala revealed <em>Pinus hartwegii</em> trees in both planted and natural forests in San Carlos Sija, with typical symptoms of pitch canker. These included flagging of the branches and thick, resinous pitch surrounding cankered areas on the stems. Similar symptoms were also observed on a single individual <em>P. oocarpa</em> tree in Nicaragua. DNA-based identification of isolates from diseased trees confirmed the presence of <em>F. circinatum</em>. Two haplotypes were identified using microsatellite markers and both mating types were present in Guatemala. In South Africa, <em>P. oocarpa</em> has been extensively used as a tolerant hybrid partner with other <em>Pinus</em> spp. to offset the negative impact of pitch canker. Tolerance of these hybrids to the newly discovered haplotypes of <em>F. circinatum</em> was tested in an inoculation trial. Seedlings representing five commercial families of the <em>P. patula </em>x<em> P. oocarpa </em>hybrid were inoculated and the pure species <em>P. tecunumanii</em> LE (low elevation population) and <em>P. patula </em>were included for comparative purposes. Tolerance levels were assessed based on lesion development. Results showed that the <em>P. tecunumanii</em> (LE) and the <em>P. patula </em>x<em> P. oocarpa </em>hybrids were significantly more tolerant to infection by <em>F. circinatum</em> than <em>P. patula</em>. Furthermore, the two former species showed no significant difference in tolerance to the pathogen. From this study it is clear that hybrids with <em>P. oocarpa </em>have the potential to negate the negative impact of pitch canker in South Africa, while retaining desirable traits from <em>P. patula</em>.</div>