Yet, it has also provided support for the hypothesis that the fungus may be native to these areas. This diversity indicates that sexual reproduction is more common than previously thought, particularly as the sexual stage (previously known as Mycosphaerella pini) has only rarely been observed, and the asexual stage is ubiquitous. Individual population studies have shown unexpected levels of diversity in many populations. However, a comprehensive global population study to investigate the role of pathogen genotype and population has not been conducted to date. A number of studies have concluded that contributing factors to this disease escalation are increased host availability through the expansion of plantation forests, often of more susceptible non-native hosts, and changing climatic conditions, particularly above-average precipitation.

Reasons for this increase in incidence and severity in the last 30 years has been ascribed to various aspects of the disease triangle: host genotype, pathogen genotype and environment. Since the 1990s, however, DNB has increased in incidence and severity in the Northern Hemisphere, with severe largescale outbreaks occurring in Canada, the UK, and France, and with the disease being reported for the first time from much of central and northern Europe. septosporum to be in Eastern Europe (i.e., the Baltic and Western Russia) and Western Asia.ĭNB achieved notoriety in the 1950s and 1960s in the Southern Hemisphere, where it caused and continues to cause extensive damage to non-native pine plantations. The study strongly suggests the native range of D. All clusters and subclusters contained both mating-types of the fungus, indicating the potential for sexual reproduction, although asexual reproduction remained the primary mode of reproduction. The Turkish subcluster diverged first, followed by the Central European subcluster, then the Western European cluster, which has subsequently spread to much of the Southern Hemisphere.

The Northeastern European subcluster was shown to be ancestral to all other European clusters and subclusters. Modeling of historical scenarios using approximate Bayesian computation revealed the North American cluster was derived from an ancestral population in Eurasia. When over 3800 isolates were examined, three major population clusters were revealed: North America, Western Europe, and Eastern Europe, with distinct subclusters in the highly diverse Eastern European cluster. This comprehensive global population study elucidated the historical migration pathways of the pathogen to reveal the Eurasian origin of the fungus. Its wide host and environmental ranges have led to its global success as a pathogen and severe economic damage to pine forests in many regions. Dothistroma septosporum, the primary causal agent of Dothistroma needle blight, is one of the most significant foliar pathogens of pine worldwide.