Endocronartium harknessii

Pine-pine gall rust
Endocronartium harknessii
Scientific classification
Kingdom:	Fungi
Division:	Basidiomycota
Class:	Urediniomycetes
Order:	Uredinales
Family:	Cronartiaceae
Genus:	Endocronartium
Species:	E. harknessii
Binomial name
Endocronartium harknessii (J.P.Moore) Hirats. (1969)

Pine-pine gall rust, also known as western gall rust, is a fungal disease of pine trees. This plant disease is caused by Endocronartium harknessii (asexual name is Peridermium harknessii), an autoecious, endocyclic, rust fungus that grows in the vascular cambium of the host. Pine-pine gall rust is found on pine trees (Pinus spp.) with two or three needles such as ponderosa pine, jack pine, and scots pine. The disease is very similar to pine-oak gall rust, but its second host is another Pinus species. The fungal infection results in gall formation on branches or trunks of infected hosts. Gall formation is typically not detrimental to old trees but has been known to kill younger less stable saplings. Galls can vary from small growths on branch extremities to grapefruit sized galls on trunks.

The hosts of the aecial stage of the fungus includes two and three needled Pinus spp. The most important aecial hosts include jack pine (P. banksiana), lodgepole pine (P. contorta), western yellow pine (P. ponderosa), and the European Scots pine (P. sylvestris). A variety of other pines, such as Pinus nigra, P. mugo, P. palustris, P. banksiana, P. muricata, and P. radiata have also been reported as hosts to pine-pine gall rust (E. harknessii), but these pine species are considered less valuable. Because E. harknessii is an autoecious short-cycle rust lacking telial a host, there is no alternative hosts. The pathogen can infect actively growing shoots of any age very quickly without infecting an alternative host, making the disease cycle more destructive that typical rust species that switch between hosts. This also prevents control of the fungus by management of the alternative host species.

Symptoms of pine-pine gall rust can be quite conspicuous and are useful for diagnostic identification. The most prominent symptoms are hip cankers and swollen, spherical to oblong growths (galls) on the branches, stems, or main trunk of the host. The galls on small twigs of 1–2 years of age are often pear-shaped. Gall formation results from the overproduction of xylem tissue stimulated by the fungus. Witches brooming occasionally occurs along with galling. The bark on large galls will slough off over time, exposing the smooth wood beneath. Signs of pine-pine gall rust include the pale yellow aecia (1-8mm in diameter) formed on galls in spring as well as the yellow-orange aeciospores contained within. Immature galls are spindle-shaped. Infections usually occur on more succulent (thick) branches. When mature, galls can grow as large as a softball (30.5 cm circumference), but most are the size of a golf ball (4.2 cm). Before the production of spores, the needles on highly infected branches become chlorotic or red, eventually turning brown when the branch dies. Western gall rust can cause dwarfing to occur if leader stem of younger pines are infected. Early identification of the disease is important for treatment, but is often hard to diagnose due to the inconspicuous initial symptoms and a lack of galls until the second year. A red pigmentation may develop on the epidermal galls of P. contorta seedlings 14–28 days after infection, but this is not always a reliable indicator.

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Wikipedia