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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 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. Keywords: disease tolerance, Fusarium circinatum, hedge mortality, hydroponic, pine propagation, Pinus patula, Pinus tecunumanii, polythene bags, rooting, sand bedsSouthern Forests 2014, 76(3): 167–175

Fusarium circinatum is an important fungal pathogen of Pinus species. In South Africa, it is the most significant pathogen of Pinus patula seedlings in forestry nurseries where it presents a substantial constraint to productivity and can continue to cause mortality in-field for up to two years after establishment. This study describes the results from two trials where P. patula seedlings were inoculated with F. circinatum to determine the impact of the pathogen on nursery and field performance. Seedlings were also subjected to water stress treatments to ascertain whether this would trigger the onset of disease symptoms. Inoculum load and timing of inoculation had significant effects on seedling survival in both the nursery and field. High inoculum concentrations caused greater levels of mortality and, where seedlings were inoculated at a young age, they showed higher levels of susceptibility to F. circinatum. Temporary water-stress in the nursery produced smaller plants and improved in-field survival, but this treatment did not trigger higher mortality in inoculated treatments. On the other hand, transplant stress was a major contributor to the higher levels of mortality observed in inoculated treatments. Overall, these studies confirmed that infection in the nursery leads to the disease problems observed during early plant establishment in the field.Keywords: Fusarium circinatum, inoculation, nursery-to-field, Pinus patula, seedlings, survivalSouthern Forests 2014, 76(3): 125–136

Fusarium circinatum is a pathogen causing serious post-planting mortality of Pinus patula seedlings in southern Africa. Containerised planting stock that is asymptomatic but associated with F. circinatum in the nursery is thought to be the cause of this problem. The aim of this study was to determine if re-use of seedling containers could be a source of inoculum resulting in asymptomatic planting stock and increased post-planting mortality of P. patula. Two experiments were conducted in successive years comparing nursery cull of symptomatic seedlings, seedling growth, association of F. circinatum with asymptomatic seedlings and post-planting mortality for crops raised in re-used containers, with and without sanitation, and factory-new containers. Each experiment consisted of a nursery production trial followed by out-planting into pots to assess post-planting mortality. Our results show that re-use of containers without sanitation increases the cull of symptomatic seedlings, incidence of F. circinatum associated with asymptomatic seedlings and post-planting mortality compared with the re-use of containers after steam sanitation or factory-new containers. Growth of asymptomatic seedlings was unaffected by container treatment or association with F. circinatum and in the absence of wilt symptoms the root system did not exhibit typical discolouration. Watering frequency did not influence post-planting mortality in pots. The comparison of two open-pollinated seed mixes of P. patula that, based on seedling stem inoculation screening, represented susceptible and tolerant material did not show differences in nursery cull or post-planting mortality. This work demonstrated that natural contamination of re-used containers can be a primary source of inoculum producing asymptomatic seedlings associated with F. circinatum that will succumb to the pathogen after field planting. The process of seedling infection, apparent latent infection in the seedling and expression of disease after planting needs greater understanding to improve nursery hygiene measures to control this disease.Keywords: containerised seedling nursery, Fusarium circinatum, Pinus patula, post-planting mortalitySouthern Forests 2014, 76(3): 177–187