Surveys for asymptomatic persistence of Sphaeropsis sapinea on or in stems of red pine seedlings from seven Great Lakes region nurseries

Abstract

The fungus Sphaeropsis sapinea persists on or in stems of asymptomatic red pine (Pinus resinosa) nursery seedlings, and proliferates to cause collar rot and mortality after planting. In the spring of 2002, seven nurseries were surveyed to determine the potential range in frequency of asymptomatic persistence: three operated by Wisconsin Department of Natural Resources (DNR), two by Minnesota DNR, one by Michigan DNR, and one by USDA Forest Service (in Michigan). At each nursery five groups of 20 asymptomatic red pine seedlings were collected near an inoculum source (red pine windbreak), if present, and five groups of 20 asymptomatic seedlings were collected away from such a source (1400 seedlings total). A segment of the lower stem/root collar from each seedling was surface disinfested and incubated on tannic acid agar. Transfers were made from resulting colonies and the pathogen identified from pycnidia and conidia produced in culture. The pathogen was identified from asymptomatic seedlings collected in all Wisconsin and Minnesota nurseries, but was never detected from seedlings from the Michigan DNR or USDA Forest Service nurseries. Frequencies of detection were greater (as high as 88%) from asymptomatic seedlings near red pine windbreaks including diseased trees than from seedlings distant from such windbreaks. A subset of isolates from asymptomatic seedlings was characterized using inter-simple sequence repeat-polymerase chain reaction analysis. Most isolates were the A group of S. sapinea, but B group isolates (recently named Diplodia scrobiculata) were also obtained from one nursery. One Minnesota nursery was more extensively sampled in 2003, with 17-44 groups of five asymptomatic red pine seedlings collected in four separate fields (525 seedlings total). The mean frequency of detection of the pathogen in these four fields ranged from 40 to 71%. Persistence of S. sapinea on or in asymptomatic seedlings continues to be problematic, not only because of the potential for subsequent seedling mortality, but also as a means by which a pathogen may be widely distributed.

Distribution of Diplodia pinea and its genotypic diversity within asymptomatic Pinus patula trees

“…causing shoot die-back, stem cankers, seedling mortality and under stress conditions such as hail damage, tree mortality (Swart et al 1987;Blodgett et al 1997;Burgess and Wingfield 2001;Stanosz et al 2001). Diplodia pinea can be an endophyte in asymptomatic Pinus tissue (Smith et al 1996;Burgess et al 2001a;Stanosz et al 2005;Maresi et al 2007) and is commonly encountered as a saprophyte on cone bracts and coarse woody debris (Smith et al 1996;Flowers et al 2001;Santini et al …”

Sources of Diplodia pinea endophytic infections in Pinus patula and P. radiata seedlings in South Africa

“…2007). In South Africa, seedlings are raised in trays on metallic beds that are closed with screens, whereas in USA, seedlings are often raised bare rooted under open conditions and surrounded by mature Pine tree windbreaks (S tanosz and C arlson 1996; S tanosz et al. 2005, 2007).…”

“…Diplodia pinea is commonly isolated from seedlings in nurseries (P almer and N icholls 1985; S tanosz et al. 2005, 2007) and from different parts of pine species including, needles, cones, branches, seed scales, seeds and piths of cones and mature wood (V ujanovic et al.…”

Detection of the Diplodia shoot blight and canker pathogens from red and jack pine seeds using cultural methods

“…High incidence and severity of Diplodia shoot blight in bare-root seedling nurseries in Minnesota and Wisconsin historically has been associated with inoculum disseminated from infested red pine windbreaks adjacent to seedling beds (Palmer et al 1988;Stanosz et al 2005). Diplodia pinea can also persist on or in asymptomatic seedlings and later proliferate to cause disease symptoms, including mortality, under conditions that induce host stress (Stanosz et al , 2001.…”