faty
Get Complete Project Material File(s) Now! »
Infection and Dispersal
Infection of mature or established plantation trees by F. circinatum is reported to occur only through wounds that act as infection sites (Dwinell and Barrows-Broaddus 1981; Storer et al. 1998). These are commonly made by twig, bark and cone beetles such as species of Ips, Conophthorus,Ernobius and Pissodes nemorensis, which are also known to vector the pathogen (DeBarr and Barrows Broadduss 1986; Storer et al. 1998; Coutinho et al. 2007). It is believed that the general absence of bark and twig-boring insects in South Africa is a possible reason that outbreaks of pitch canker on mature pine trees has remained absent for so long (Wingfield et al. 1999, 2002b). A notable exception is P. nemorensis, which is a well-established pest in South African pine plantations (Gebeyehu and Wingfield 2003). This insect was also found associated with the symptomatic trees examined in the Western Cape region where the first outbreak of pitch canker was detected (Coutinho et al. 2007). However, the exact role of P. nemorensis in the epidemiology of the disease in South Africa remains to be determined, because pitch canker could be facilitated by a number of other wounding or vectoring agents. For example, baboons have become a serious pest in stripping bark from trees (McNamara 2006). The pathogen can also gain access to the host through pruning wounds (Sakamoto and Gordon 2006). In the reported pitch canker outbreak on mature P. radiata in the southern Cape (Coutinho et al. 2007), stem cankers were frequently found developing around pruned branch whorls (Fig. 2d) and baboon damage sites (Fig. 2c). Based on these facts, it would seem that there is sufficient wounding on mature trees to facilitate the rapid spread of the disease in South Africa.
Nursery
Controlling F. circinatum in pine nurseries remains the most important means of reducing field mortality at establishment. Some nurseries report that the control of F. circinatum is particularly difficult, while others report better control. This may be because nurserymen do not wish to disclose the extent of the problem, but there may also be some scientific evidence for this observation. Previous studies on F. oxysporum have indicated large variation in virulence for different isolates on nursery seedlings (James and Gilligan 1984), and also differences in virulence of isolates collected from different nurseries (James et al. 1999). Similarly, the same has been shown for different isolates of F. circinatum (Dwinell, 1978; Gordon et al. 2001). This suggests that isolates, unique to specific nurseries in South Africa, may have resulted in the observed differences in the severity of outbreaks between other nurseries in South Africa. Nevertheless, nurserymen have now come to accept that once F. circinatum is present in their nurseries, eradication is almost impossible. At best, the disease can be managed through an integrated management approach. Maintaining effective nursery hygiene is practiced by nurserymen and nurseries are audited annually by the Seedling Growers Association of South Africa to ensure high standards. Nurserymen are required to regularly remove dying seedlings and dispose of them by removal from the site or burning (PFWG 2004).
The future of Pinus patula in South Africa
The susceptibility of P. patula to F. circinatum will severely impact the future deployment of the species in this country. Although the problem remains confined at this stage to reestablishment failure, there is the likelihood that F. circinatum could result in pitch canker on mature P. patula and other pine trees. This highlights the urgent need to reconsider the deployment of P. patula, not only to limit further spread in South Africa, but also to prevent the spread of the fungus into the rest of Southern Africa.
The current lack of effective control in nurseries and in young field plantings increases the risk and cost to propagate this species. Chemicals, biocontrol agents and even increased nursery hygiene appear to have limited effect. Selection and breeding more tolerant families appears to be the only feasible solution to the problem if breeders wish to continue with the deployment of P. patula. In order to improve the tolerance of the current breeding populations, greenhouse screening studies are the most simple and rapid technique available to breeders. Such studies should effectively distinguish those families that are highly tolerant from those that are highly susceptible in field infections (Vogler and Kinloch 1999). Due to the general lack of tolerance of P. patula to F. circinatum, especially at the seedling stage, it may be too ambitious to expect that, by deploying the more tolerant families from greenhouse studies, the field survival problem will be resolved. Although there may be some improvement in field survival the importance of greenhouse screening trials is to identify families which, as mature trees, will be more tolerant to pitch canker. A drawback of this method is that seed quantities are drastically reduced as the more tolerant clones are selectively harvested in orchards. Immediate deployment of these families, therefore, may have to rely on vegetative propagation (Gordon et al. 2001). The best long-term solution would be to establish new clonal seed orchards of selected clones.
Chapter 1: The pitch canker fungus, Fusarium circinatum; Implications for South African forestry. (Southern Forests, 2011, vol. 73: 1-13)
Abstract
Introduction
Symptoms
Infection and dispersal
Economic impact
Disease management
Long-term management strategies
The future of Pinus patula in South Africa
Acknowledgements
References
Chapter 2: Selection of Pinus spp. in South Africa for tolerance to infection by the pitch canker fungus (New Forests, 2012, vol. 43:473-489)
Abstract
Introduction
Materials and methods
Inoculation procedures
Statistical analysis
Results
Discussion
Conclusion
Acknowledgements
References
Chapter 3: The tolerance of Pinus patula x Pinus tecunumanii, and other pine hybrids, to Fusarium circinatum in greenhouse trials (New Forests, 2012, DOI: 10.1007/s11056-012-9355-3)
Abstract
Introduction
Materials and methods
Inoculation procedures
Statistical analysis
Results
Discussion
Acknowledgements
References
Chapter 4: Susceptibility of provenances and families of Pinus maximinoi and Pinus tecunumanii to frost in South Africa (New Forests, 2012 DOI: 10.1007/s11056-012-93)
Abstract
Introduction
Methods
Statistical analysis
Results
Discussion
Conclusion and outlook
Acknowledgements
Reference
Chapter 5: Tolerance of Pinus patula full-sib families to Fusarium circinatum in a greenhouse study
Abstract
Introduction
Materials and methods
Statistical analysis
Results
Discussion
Acknowledgements
References
Chapter 6: Tolerance of Pinus patula seedlings and established trees to infection by Fusarium circinatum
Abstract
Introduction
Materials and methods
Statistical analysis
Results
Discussion
Acknowledgements
References
Chapter 7: Future outlook for Pinus patula in South Africa in the presence of the pitch canker fungus (Fusarium circinatum)
Abstract
The history of P. patula in South Africa
Current status
Opportunities to improve tolerance
Large scale production of improved material
Operational deployment
Acknowledgements
References
