The pathogenicity of Diplodia pinea to Pinus radiata D. Don

Abstract

In the Pinus radiata stands of north-eastern Victoria the symptom "dead top" is common and consistently associated with the fungus Diplodia pinea. In order to resolve the pathogenic status of D. pinea, its association with disease symptoms has been studied by histological examination and tissue isolations following greenhouse and field inoculations. Malformations were associated with infection by D. pinea and although the amount of tissue killed was small, the defect induced was considerable. Damage to the leader caused the greatest loss in wood quality. The fungus attacked the pith very readily after gaining access to this tissue through injuries and via needle or cone traces. In the pith, the fungus spread slowly downwards and was protected from changes in the external environment. Injection of D. pinea spores into the pith resulted in a very high percentage of infection, and caused the malformations and other symptoms associated with attack by this fungus in the field. Histological studies showed that the fungus spread rapidly in the pith tissues, causing alterations in cambial function which produced traumatic resin canals, parenchymatous cells, and compression wood. Field trials showed that fast-growing trees were more severely affected than slower-growing ones, and the latter recovered more quickly. The fungus persisted in the infected tissues for up to 400 days.

Comparison of genotypic diversity in native and introduced populations of Sphaeropsis sapinea isolated from Pinus radiata

“…In addition, P. radiata growing on poor or badly drained sites, susceptible to water logging and drought, were also vulnerable to damage by S. sapinea in winter rainfall areas of South Africa (Laughton 1937). Similar drought-associated losses have been experienced in New Zealand (Thomson 1969) and Australia (Marks & Minko 1969, Davison, Tay & Peroni 1991.…”

Characterization of Sphaeropsis sapinea Isolates from South Africa, Mexico, and Indonesia

“…Infection by S. sapinea results in various disease symptoms, of which dieback is the most common (17). Other symptoms frequently associated with S. sapinea infec-tion include whorl cankers (16,38), root disease (37), and crown wilt (8). The fungus was also found as a saprophytic inhabitant of sapwood, resulting in blue stain (13).…”

Geographic isolation of Diplodia scrobiculata and its association with native Pinus radiata

“…Likewise, D. pinea may not be a native to Mexico, which would be consistent with the fact that the native Mexican pine, P. patula is very susceptible to die-back caused by D. pinea (Gibson 1979, Zwolinski et al 1990. Similarly, P. radiata which appears not to be associated with D. pinea in its native range, is highly susceptible to this pathogen in the exotic environment (Laughton 1937, Marks & Minko 1969, Thomson 1969, Lundquist 1987.…”

“…in many parts of the world (Punithalingam & Waterson 1970, Swart, Wingfield & Knox-Davies 1985, Zwolinski, Swart & Wingfield 1990, Burgess & Wingfield 2002. In Southern Hemisphere plantations, P. radiata is known to be particularly susceptible to D. pinea when planted off-site in regions with summer rainfall, hail, drought or waterlogging (Marks & Minko 1969, Thomson 1969, Gibson 1979, Lundquist 1987, Zwolinski et al 1990, Davison, Tay & Peroni 1991, Burgess & Wingfield 2001.…”