Pinus patula and pine hybrid hedge productivity in South Africa : a comparison between two vegetative propagation systems exposed to natural infection by Fusarium circinatum

In response to the Fusarium circinatum pine pathogen threat in southern Africa, research has been conducted on the development of F. circinatum-tolerant P. patula and P. patula hybrids. The objective of this study was to investigate the propagation potential of these taxa in two vegetative propagation systems, hydroponic sand beds and polythene bags with composted pine bark growing medium. Significant differences (p< 0.001) in mortality associated with F. circinatum were observed between the P. patula x P. tecunumanii (LE) hybrid (6%) and P. patula (19–23%). No significant differences in mortality associated with F. circinatum were observed within P. patula x P. tecunumanii (LE) families, which ranged from zero to 15%. Significant mortality differences (p < 0.001) were observed between P. patula families, which ranged from 8% to 44%. The number of rooted cuttings produced, per hedge established, over the four-year period was significantly better (p  0.001) in the P. patula x P. tecunumanii (LE) hybrid (52) than in P. patula (29–33). Significant differences (p < 0.001) were also observed in the number of rooted cuttings produced per family, with P. patula x P. tecunumanii (LE) families ranging from 35 to 70 cuttings per hedge plant established and P. patula families between 20 and 42 cuttings. Over the four-year duration of the trial all taxa showed increased productivity in hedges grown in a hydroponic sand bed system, which received more consistent fertilisation and yielded an average of 55 rooted cuttings per hedge, over those grown in polythene bags with composted pine bark medium, which yielded 41 cuttings on average. This study demonstrated that the P. patula x P. tecunumanii (LE) hybrid is a feasible substitute for P. patula in both vegetative propagation systems, as it not only shows improved survival, through increased F. circinatum tolerance, but also improved productivity.