Chapter 18 - Pine pitch canker (PPC): An introduction, an overview

Abstract

Pine pitch canker (PPC) is a serious disease of Pinus spp. and Pseudotsuga menziesii globally. The infection of its causal agent, Fusarium circinatum, causes pitch or resin-soaked cankers on trunks and lateral branches of mature hosts. In nurseries, the main symptoms are damping off and tip dieback of seedlings. However, the pathogen, with a hemibiotrophic nature, can remain endophytic in seedlings that do not show symptoms of infection. Since the first report in 1946 in North America, the presence of F. circinatum has been notified in 14 countries in America, Asia, Africa, and Europe. Several factors have contributed to the spread of the disease to all these continents, the most important being globalization in terms of trade in reproductive plant material. Wind, raindrops, and forest insects associated with pines contribute to the local dispersion of the pathogen. Therefore, the implementation of early diagnostic methods is crucial to prevent the PPC establishment in disease-free areas. Worryingly, some herbaceous plants growing under the canopy of PPC-affected stands may also act as a source of inoculum for F. circinatum, as recent studies have reported. Since the viability of the inoculum is highly moisture dependent and needs warm temperatures to germinate, coastal areas represent the most suitable climate for PPC development. In fact, the highest incidence occurs in Mediterranean and subtropical climates and temperate regions. Under future climate change scenarios, cooler latitudes with the presence of susceptible hosts would become suitable for the disease establishment. For this reason, the use of tolerant host conifers might reduce outbreaks of PPC in free-disease areas. The range of susceptibility to F. circinatum has been found to vary significantly among species and intraspecifically, posing as a potential disease management strategy. According to this, the development of massive sequencing technologies is allowing a deeper understanding of the plant-pathogen interaction of this pathosystem, promoting the improvement of breeding programs to obtain resistant pine reproductive material. Eco-friendly methods such as the use of endophytic fungi and bacteria with antagonistic effect to F. circinatum, plant essential oils, chitosan, or phosphite have been also investigated for reducing the impact of the PPC. Moreover, thermotherapy to eliminate the pathogen from infected seeds is a simple and low-cost method to minimize the risk of introducing contaminated seed into nurseries in disease-free areas. However, the lack of effective intervention measures in the field and the difficulties to avoid its transmission to the forest due to asymptomatic nursery plants make PPC an unsolved problem for the coming years. Therefore, great efforts will be necessary to address the integrated management of this disease through the use of environmental-friendly methods in the near future.