M.J. Wingfield, A. Jacobs, T.A. Coutinho*, R. Ahumada and B.D. Wingfield
Department of Microbiology and Plant Pathology, Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, Pretoria 0001, South Africa
Accepted: 28 Dec 2001
Pitch canker, caused by Gibberella circinata (Fusarium circinatum), is currently regarded as one of the most serious diseases of pines in the world. The disease was first discovered in the south-eastern United States in the early 1900's and subsequently, has caused sporadic occurrences of severe disease in that area. More recently, the disease appeared in California where it is currently causing a serious epidemic on native Pinus radiata, which is of international concern (Gordon et al., 2001).
Pinus radiata forms the basis of extensive areas of exotic forest plantation in many countries in the Southern Hemisphere. For this reason, pitch canker is viewed as one of the greatest threats to globally relevant forest industries in these areas. Consequently, various international programmes have been established in an attempt to reduce this threat (Devey et al., 1999).
During the course of recent surveys in the Conception area of Chile, dying P. radiata plants have been discovered in both containerised and open rooted clonal hedges. Plants appear to die rapidly and typically display resin exudation from the root collar areas and pitch-soaked wood associated with these lesions. Isolations from symptomatic tissue have consistently yielded cultures of Fusarium belonging to the Fusarium subglutinans species complex. Isolates have sterile hyphal coils strongly reminiscent of F. circinatum. Single conidial cultures paired with mating tester strains of the "H" mating population (Britz et al., 1999) consistently showed sexual compatibility. To further confirm their identity, a PCR-RFLP test based on histone H3 gene sequences (Steenkamp et al., 1999) was used on 6 isolates to compare them with members of the F. subglutinans species complex. This technique reliably distinguishes F. circinatum from other species in this complex. Results confirmed morphological comparisons and mating compatibility tests showing that the fungus associated with dying plants in Chile is F. circinatum.
Although F. circinatum is causing damage to P. radiata plants in Chilean nurseries, it has as yet, not been found on trees in plantations. In this sense, the situation is similar to that in South Africa, where the pathogen causes serious damage to seedlings in nurseries but is not associated with typical symptoms of pitch canker. The fact that P. radiata is highly susceptible to infection by F. circinatum and that this tree forms the basis of the local forestry is of significant concern. This concern is heightened by the fact that various insect pests of P. radiata are present in Chile that are capable of providing infection sites for the pitch canker fungus. Consequently, various strategies linked to tree breeding and selection have been established to minimise the long-term threat of pitch canker in Chile.
Britz H, Coutinho TA, Wingfield MJ, Marasas WFO, Gordon TR, Leslie JF, 1999. Fusarium subglutinans f.sp. pini represents a distinct mating population in the Gibberella fujikuroi species complex. Applied and Environmental Microbiology 65, 1198-1201.
Devey M, Matheson C, Gordon T, Eds. 1999. Current and potential impacts of pitch canker in Radiata pine. Proceedings of the IMPACT Monterey Workshop, Monterey, California, 30 November to 3 December 1998. CSIRO, Australia.
Gordon TR, Storer AJ, Wood, DL, 2001. The pitch canker epidemic in California. Plant Disease 85, 1128-1139.
Steenkamp ET, Wingfield BD, Coutinho TA, Wingfield MJ, Marasas WFO, 1999. Differentiation of Fusarium subglutinans f.sp. pini by histone gene sequence data. Applied and Environmental Microbiology 65, 3401-3406.
©2001 The Authors