Smith (1967) noted whereas F. oxysporum was recovered from the roots of 90% of sugar pines when trees were lifted from nursery soil, this fungus was not detectable on roots of sugar pines four years after outplanting in the forest.... F. oxysporum is rarely recovered from forest soils.... Predictions of the model were consistent with the distribution of pitch canker in North America, where the disease has been established long enough to have approached ecological limits on its geographic range."
EXCERPT 2 (absent the internal citations): "Pitch canker, caused by Fusarium circinatum, was first recognized as a disease in the state of North Carolina in the U.S. in 1945. The pathogen was isolated from cankers that were characterized by extensive production of resin, which inspired the name 'pitch canker' for the disease. Pitch canker subsequently became more widespread in the southeastern U.S. (SE U.S.), where it continues to cause problems for production of pines in plantations, seed orchards, and seedling nurseries. The disease was discovered in California in 1986, followed by confirmed reports from Japan, South Africa, Mexico, Spain, South Korea, Chile, Italy, Portugal, Colombia, and Brazil. The host range of F. circinatum extends to more than 60 species of Pinus and also includes Douglas-fir, the only conifer outside the pine genus known to be susceptible. Under experimental conditions, F. circinatum is capable of colonizing maize (Zea mays L.) asymptomatically, and natural infections of grass hosts have been confirmed in the U.S. and in South Africa. No symptoms have been observed on infected grasses, suggesting the relationship is commensal. The significance of an association with grasses has yet to be established but could influence disease development, as described below."
EXCERPT 3: Fusarium circinatum is not a common resident in soil and so is not likely to be a problem in seedling nurseries unless introduced with contaminated soil or seed. If the pathogen is not already established in soil nearby, seed is the most likely vehicle for introduction. F. circinatum has been confirmed to occur both on and within seeds of several pine species. Superficial contamination of seed is common in areas where pitch canker occurs, regardless of the disease status of the tree from which cones are obtained. Such infestations are presumably due to deposition of airborne microconidia and macroconidia, both of which F. circinatum can produce on infected host tissue. Spores might germinate on seed, but whatever subsequent growth occurs appears not to extend beyond the seed coat because topical treatments with various anti-microbial materials will eliminate the pathogen. For example, seeds collected from healthy Pinus radiata in stands affected by pitch canker commonly carry the pathogen, but the incidence of infestation can be reduced to zero by immersion of seeds in an aqueous solution of 1.0% sodium hypochlorite.... Internally infested seeds typically suffer high mortality rates from both pre- and post-emergence damping-off. However, some seed treatments will significantly reduce the rate of mortality, which indicates that internally infested seed is capable of producing a healthy seedling if growth of the pathogen can be suppressed. Both internal and external infestations of P. radiata seed were eliminated by treatment either with benomyl or a combination of benzimidazole, carboxin and thiram, which increased seedling emergence to 53 and 57%, respectively, compared to 43% for untreated seed. No seedlings emerging from treated seed were infected with F. circinatum.
EXCERPT 4: "The potential for seedlings to sustain latent infections poses a challenge for management, because visual inspections are not sufficient to identify trees that may be carrying F. circinatum. Furthermore, greenhouse studies have shown that extensive colonization of the root system by F. circinatum may not result in visible damage. Shoot symptoms become apparent only after the fungus grows into the root collar and girdles the stem. Thereafter, F. circinatum grows more extensively in roots and can be isolated from necrotic tissue. Thus it appears that rotting of roots is a consequence of seedling death and not the cause (Swett and Gordon, 2013). If this is typical of how disease develops in seedling nurseries, inspection of roots may not be a reliable means of identifying cryptic infections."
• Note by Torreya Guardians founder Connie Barlow: The first sentence in Excerpt 1 above in red supports my own critique that any lab experimentation in Florida that injects Fusarium torreyae into potted plants or cuttings of conifer species native to the Appalachian region (especially the highest elevations, as in Red Spruce and Fraser Fir) are ecologically negligent, and thus likely would not pass peer review, and certainly should not provoke botanical gardens in Georgia to refuse sending Florida torreya seeds northward from their own ex situ seed production in northern Georgia.
Quite simply, Fusarium torreyae, like other species of the genus, ramify into pathogenic agents only in conditions of stress. As well, because techniques for discerning sophisticated morphological and molecular phylogenetic distinctions have only recently been developed, Fusarium torreyae is not the only taxonomic splitting recently recognized. In 2003, Fusarium commune was distinguished from "its putative sister taxon, the F. oxysporum complex." Prior to publication of this discovery, the authors sampled not just their Denmark location but several other locales in the northern hemisphere — and thereby established its wide occurrence (Skovgaard et al., 2003, Fusarium commune is a new species identified by morphological and molecular phylogenetic data", Mycologia). In contrast, the Aoki et al. 2013 paper announcing F. torreyae as a new species did not include any information on geographic range beyond its discovery locale. Unfortunately, this seems to have ramped up opposition to assisted migration of Florida torreya northward beyond initial concerns that the tree itself might become "invasive" in northward recipient ecosystems. Now the new conjecture is that this newly identified Fusarium might not only invade new ecosystems but do so lethally. This is a sophisticated conjecture that, when offered by respected professionals, is difficult for any non-professionals to speak against — hence this lengthy list of linked papers and excerpts that I am posting on the Torreya Guardians website.
