Overview

Phytophthora cambivora (Petri) Buisman (1927) causes root rot and stem canker on several forest species in Europe and North America.  It causes ink disease of chestnut (Day 1938, Vannini & Vettraino 2001, Vettraino et al. 2005).  Other hardwoods, especially members of the Fagaceae, such as European beech, chinquapin, and tanoak (rarely), are affected (Belisario & Maccaroni 2006, Nelson et al. 2010, Orlikowski et al. 2006, Reeser et al. 2007, Saavedra et al. 2007, Schmitz et al. 2007).

Etymology: combining the Latin for "cambium" and “devouring.”

Morphology

Phytophthora cambivora is heterothallic, forming characteristic warty, or bullate oogonia with 2-celled antheridia when paired with the opposite mating type. Sporangia are nonpapillate, about  55–65 μm by 40–45 μm, and broadly ellipsoid or ovoid. They are persistent, on simple, unbranched sporangiophores and exhibit internal, often nested proliferation as well as external extension of the sporangiophore. Chlamydospores are absent. Hyphal swellings are rare.

Genetics

Phytophthora cambivora is in phylogenetic clade 7, with P. cinnamomi, with which it shares many features. It has been implicated in the complex hybrid genealogy of P. alni (Brasier & Kirk 2001). Different mating types predominate on different hosts and in different regions: isolates of P. cambivora from chestnut in Europe and from chinquapin in Oregon are mostly mating type A2 (Saavedra et al. 2007, Vettraino et al. 2005); isolates from other forest hosts in western North America are A1.

Growth

Phytophthora cambivora grows dense aerial, fluffy colonies without pattern on most agar media. It is relatively fast growing (growth at 20°C on V8 agar 5.6 mm/d, on cornmeal agar with 20 ppm β-sitosterol 5.1 mm/d, on cornmeal agar with pimaricin, ampicillin, and rifampicin 4.6 mm/d, potato dextrose agar (PDA) 3.4 mm/d). The optimum temperature for growth is ca. 22–24°C, min. ca. 2°C, max. ca. 32°C.

Distinguishing characteristics for identification

Phytophthora cambivora is relatively easy to identify, especially if the typical bullate oogonia and 2-celled antheridia are induced in a mating test. Look-alike P. alni is homothallic. The fluffy, patternless colony morphology on agar is distinctive. Sporangia are usually slow to form, and not abundant. They are non-papillate and generally non-descript.  Phytophthora cambivora is very similar in appearance to P. cinnamomi and P. cryptogea, but can usually be distinguished by lack of chlamydospores.

The searchable web-based database Phytophthora-ID is useful for rapid identification of Phytophthora species based on sequencing of the ITS or Cox spacer regions, followed by BLAST searching the database. Phytophthora-ID maintains a database of sequences that is selective for sequence accessions that come from trusted sources including published, peer-reviewed studies whenever possible.

Disease History

Blepharospora cambivora was recognized by Petri in 1917 as the cause of “Maladie de la encre,” or ink disease of European chestnut (Day 1938, Vannini & Vettraino 2001). It was soon recognized as a Phytophthora species and transferred to that genus by Christina Buisman.  Today it is known to be a common pathogen in much of Europe on hardwood forest trees, especially members of the Fagaceae, including chestnut and beech (Belisario & Maccaroni 2006, Cerny et al. 2008, Jung et al. 2005, Nelson et al. 2010, Orlikowski et al. 2006, Schmitz et al. 2007, Vannini & Vettraino 2001, Vettraino et al. 2005). In North America, it is also implicated in root rot of chestnut in the SE United States, but P. cinnamomi proved to be most frequently involved. In 2000 P. cambivora was associated with death of chinquapin (Chrysolepis chrysophylla) forest trees in south central Oregon (Saavedra et al. 2007). It is occasionally isolated from basal cankers on tanoaks (Reeser et al. 2007).  P. cambivora is also known as a pathogen of fruit trees.

Impacts in the Forest

Phytophthora cambivora, as the cause of ink disease in Europe, may have dramatic economic and ecological consequences in chestnut orchards, high forest, coppices or natural lands, especially in France, Italy and Greece (Vannini & Vettraino 2001, Vettraino et al. 2005). In Germany and nearby countries it is important among the group of Phytophthora species causing bleeding cankers and ultimately mortality on European beech (Belisario & Maccaroni 2006, Jung et al. 2005, Nelson et al. 2010, Orlikowski et al. 2006, Schmitz et al. 2007). It is having a similar impact, although in a much more limited area, on chinquapin in Oregon (Saavedra et al. 2007). P. cambivora causes scattered mortality of other forest trees in Europe (Greslebin et al. 2005, Talgø et al. 2006, Vettraino et al. 2003, Yakabe et al. 2009). P. cambivora has been recovered from forest soils and streams throughout western Oregon, as well as oak forest soils in the eastern United States and Europe, although usually there are no associated symptoms on the trees (Balci et al. 2007, Reeser et al. 2011, Vettraino et al. 2002).

Forest and Wildland Hosts and Symptoms

P. cambivora causes root rot and stem cankers on several forest tree species. The symptoms of ink disease of chestnut are typical. Necrosis of feeder or main roots may spread to the collar and the trunk, resulting in the cortical flame shaped lesions with black exudates for which the disease is named (Vannini & Vettraino 2001, Vettraino et al. 2005). Root destruction leads to above ground symptoms, including chlorosis, microphylly, and wilting. These can be followed by a quick or a progressive death depending on the environmental conditions (Vannini & Vettraino 2001, Vettraino et al. 2005). Affected chinquapin trees exhibit girdling basal cankers marked by red-brown inner bark tissues, extending upward from necrotic main roots (Reeser et al. 2007). Cankers on beech in Europe and elsewhere are also marked by bleeding spots but the discoloration of inner bark in active lesions is less dramatic. Bole cankers caused by P. cambivora on tanoak are infrequent, but indistinguishable from those caused by P. ramorum (Reeser et al. 2007).

Educational and Management Materials

• Ferma Il Mal dell'inchiostro del castagno
• Scheda Mal dell'Inchiostro
• Recommandations pour la production de plants forestiers