The fungus, Phytophthora cinnamomi Rands, is a soil-borne pathogen which causes diseases of various types on more than 900 plant species (2, 4, 5, 6, 11, 12). Well known to foresters for its involvement in littleleaf disease of Pinus spp., particularly shortleaf pine (P. echinate Mill.) (2, 3, 11), P. cinnamomi has also played significant roles in the demise of the American chestnut (Castanea dentate (Marsh.) Borkh.) (4), the devastation of some 100,000 hectares (247,000 acres) of jarrah (Eucalyptus marginata Donn. ex Sm.) forests in western Australia (6, 7, 8), and root diseases on a variety of commercially important tree species in forest nurseries in the United States (2, 4, 5).
Ross and Marx (9, 10) reported P. cinnamomi associated with mortality and Armillariella tabescens (Scop. ex Fr.) Singer (Clitocybe tabescens Bres.), another root rot pathogen, in several sand pine (Pinus causa (Chapm.) Vasey) plantations in north Florida and south Georgia. More recently, Barnard et al. (unpublished) have isolated P. cinnamomi from roots and/or soil from beneath 9 of 14 planted stands (plantations and seed orchards) suffering from root disease in north and north central Florida. On several occasions, this was the only known pathogen isolated from individual trees or individual stands. The fungus has not been found in any of 12 natural sand pine stands examined (9, 10, and Barnard et al., unpublished).
The pathogenicity of P. cinnamomi to seedlings of both the Choctawhatchee (P. causa var. immuginata Ward) and Ocala (P. causa var. causa Ward) races of sand pine has been demonstrated by Ross and Marx (10). After 2 months in greenhouse tests, the pathogen killed up to 96 and 60% of test seedlings belonging to the Choctawhatchee and Ocala races respectively, depending upon treatment variables. In Florida, approximately 500,000 sand pine seedlings have been lost in one commercial forest nursery over the past 2 years due to outright mortality caused by P. cinnamomi and/or related quarantine of infected stock (Barnard, unpublished).
The complete role of P. cinnamomi in the etiology of sand pine root disease is not yet fully understood, particularly in stands where it occurs in association with other known or suspected root disease fungi (1, 9, 10). However, its documented pathogenicity, known distribution, and infamous history make this pathogen one of substantial importance to timber industries and others enraged in growing sand pine.
Regardless of origin, P. cinnamomi, like other soil-borne fungi, can be spread by movement of infected nursery stock, movement of infested soils on equipment, etc., surface movement of irrigation or rainwater and/or mycelial growth through contiguous root systems of suitable host plants (5, 6, 12, 13). In addition, the pathogen is capable of surviving for years in infested soils in the absence of a suitable host (5, 12). Effective control programs must consider these aspects of the pathogen's biology.
Fig. 1 A, B, C. (88K)
A; Damage to sand pine caused by Phytophthora cinnamomi:
B; mortality of seedlings in a forest tree nursery; B) infected feeder roots showing sloughing of darkened, necrotic cortex
tissue, and adventitious root development (arrows);
C; mortality in a 4-year old plantation.
In the field, infected trees exhibit the same pattern of aboveground symptom development, although by virtue of seedling/tree size and/or other environmental factors, the interval between the onset of initial symptoms and eventual mortality may be extended (Fig. 1:C). In addition, some infected trees remain green, but show symptoms of decline or stress by a progressive thinning of their crowns. Infected roots in field situations usually exhibit some degree of external resinosis, and as a result, soil often adheres in clumps to roots of diseased trees. Sometimes external resinosis is evident on the stems of infected trees at or near the ground line. Internally, woody roots and root collars of diseased trees generally show some degree of resin impregnation. With increasing stand age, diseased trees become increasingly susceptible to windthrow due to the progressive loss of roots vital to their support. At this stage the involvement of other known or suspected root rot pathogens is common (1, 9, 10), and the specific roles of each in the root disease complex are less than completely understood.
Because only symptoms of P. cinnamomi infections are evident in nursery and field situations and these symptoms are not pathogen-specific, laboratory confirmation is essential for positive diagnosis.
1. Regulatory methods including meticulous inspection and phytosanitary certification of nursery seedling crops, with the application of rigid quarantines where appropriate.
2. Avoid planting sand pine in environments which are conducive to the activity of the pathogen; i.e., heavy, poorly drained soils or soils with a shallow impervious layer.
3. Avoid movement of infested soils by adequately cleaning machinery, etc., which has- been operating in areas of known pathogen activity.
4. Consider alternative, apparently less susceptible species (e.g., slash or longleaf pine) when regenerating sites where the pathogen's presence is known and such alternatives are silvicuturally acceptable.
*Forest Pathologist, Divisions of Forestry and Plant Industry. Contribution No. 489, Bureau of Plant Pathology, P. O. Box 1269, Gainesville, FL 32602.
1. BARNARD, E. L., S. H. KRATKA, G. M. BLAKESLEE, and S. W. OAK. 1979. Root disease of sand pine in Florida. Southwide Forest Dis. Wkshp. Clemson, SC (Abstr.).
2. BOYCE, J. S. 1961. Forest pathology. McGraw-Hill Book Co., New York. 572p.
3. CAMPBELL, W. A. 1951. The occurrence of Phytophthora cinnamomi in the soil under pine stands in the Southeast. Phytopathology 41:742-746.
4. CRANDALL, B. S., G. F. GRAVATT, and MARGARET M. RYAN. 1945. Root disease of Castanea species and some coniferous and broadleaf nursery stocks, caused by Phytophthora cinnamomi. Phytopathology 35:162-180.
5.KUHLMAN, E. G., and R. S. SMITH, JR. 1975. Phytophthora root rot. Pages 17-18 in: G. W. Peterson and R. S. Smith, Jr., eds. Forest nursery diseases in the United States. U.S.D.A. For. Serv. Agric. Hndbk No. 470. 125p.
6. NEWHOOK, F. J., and F. D. PODGER. 1972. The role of Phytophthora cinnamomi in Australian and New Zealand forests. Ann. Rev. Phytopathol. 10:299-326.
7. PODGER, F. D. 1972. Phytophthora cinnamomi, a cause of lethal disease in indigenous plant communities in western Australia. Phytopathology 62: 972-981.
8.____________, R. F. DOEPEL, and G. A. ZENTMEYER. 1965. Association of Phytophthora cinnamomi with a disease of Eucalyptus marginata forest in Western Australia. Plant Dis. Reptr. 49:943-947.
9. ROSS, E. W. 1973. Important diseases of sand pine. Pages 199-206 in: Sand Pine Symposium Proceedings. Southeast. For. Exp. Stn. U.S.D.A. For. Serv. Gen. Tech.Rep. SE-2. 253p.
10.______________, and D. H. MARX. 1972. Susceptibility of sand pine to Phytophthora cinnamomi. Phytopathology 62:1197-1200.
11.ZAK, B. 1957. Littleleaf of Pine. U.S.D.A. For. Serv. For. Pest Lflt. No. 20.4p.
12.ZENTMEYER, G. A. 1976. Phytophthora - plant destroyer. BioScience 26:686-689.
13____________________.. 1977. Origin of Phytophthora cinnamomi: evidence that it is not an indigenous fungus in the Americas. Phytopathology 67.1373-1377.
