LD DWINELL ¹, D ADAMS ², JJ GUERRA-SANTOS ³ and JRM AQUIRRE⁴

¹USDA Forest Service, Athens, Georgia, USA, ²California Department of Forestry, Davis, California, USA,³ Instituto de Fitosanidad, Montecillo, Mexico, and ⁴ Departamento de Agricultura, Bilbao, Spain

Background and objectives
Pitch canker, caused by Fusarium subglutinans f. sp. pini, is a serious disease of several Pinus species, including Pinus radiata (Monterey or radiata pine). The pathogen infects a variety of vegetative and reproductive pine structures at different stages of maturity and produces a diversity of symptoms. When the fungus infects the woody vegetative structures of its pine host, the host-pathogen interaction results in the formation of a resinous canker. The pitch canker fungus also causes mortality of female flowers and mature cones, deteriorates seeds of several pine species, and can cause mortality of pine seedlings in nurseries. Pitch canker, first described in 1946 in the southeastern United States, has grown from a regional problem, to one of national and international importance. Since 1986, pitch canker has seriously damaged Monterey pine in coastal central California. Pitch canker has also been found on radiata pine in Mexico and Spain. The purpose of this paper is to report on the worldwide occurrence of pitch canker in P. radiata.

Results and conclusions
Pitch canker derives its name from the copious pitch flow associated with most cankers of the trunk, branches, shoots, and exposed roots. The bark is retained, while the wood beneath the canker is deeply resin soaked. On P. radiata, most of the cankers on the primary branches occur at branch or shoot whorls or cone clusters. Developing branch or shoot cankers may show little or no external resin accumulation. However, the disease can usually be diagnosed by removing the outer bark to expose the underlying pitch-soaked wood. Diseased pine seedlings show chlorotic or reddish brown needles and wilting due to the development of girdling cankers on the stem, often resulting in mortality in the nursery or upon outplanting.

Pitch canker was unknown in California until disease outbreaks on planted Monterey pine were found almost simultaneously at 3 widely separated geographical locations. Since 1986, surveys found the disease extends from Mendocino County to San Diego; however, the disease is most severe on the central coast of California. In the past few years, the disease has become established in natural populations of Monterey pine. The causal fungus is a wound parasite and a number of insect species are involved in the disease complex. Because P. radiata originates from three mainland native populations in California, pitch canker in these populations is a severe threat to the Monterey pine genetic resource worldwide.

In Mexico, pitch canker has been reported on a number of native and introduced pine species. In 1992 , the disease was observed in a radiata pine plantation near Amecameca in the State of Mexico. Shoot dieback in the upper crown of the 20-year-old radiata pines was the main symptom. Sporodochia of the pitch canker fungus were found on diseased shoots.

Pitch canker was first observed in Europe in 1997 in the autonomous community of País Vasco (Basque Country) in northern Spain. The disease is causing the mortality of radiata pine seedlings in bare-root nurseries. Pitch canker has not been confirmed in radiata pine plantations. Surveys are being conducted to determine the incidence and severity of the disease in País Vasco.

Since pitch canker was first described in 1946, the parameters of the disease have been constantly changing. Besides the United States, Mexico, and Spain, pitch canker has been reported in Haiti on P. occidentalis and Japan on P. lunchuensis. In South Africa, the pathogen induces a root rot of containerized-P. patula. Pinus radiata is the most widely planted pine in the world. The introduction of the disease into other countries with extensive radiata pine plantations, such as Chile, New Zealand and Portugal, could be disastrous to forest products industries.