Enhancing Plantation Forest Sustainability: A Review of Eucalyptus Defence Mechanisms to Foliar Fungal Pathogens

Abstract

Purpose of the Review

In this review, we synthesize knowledge generated over many decades on the main defence responses of Eucalyptus to fungal leaf pathogens with the aim of identifying targets for breeding disease tolerant trees. We highlight physiological and molecular traits associated with host defence in relation to pathogen life-style. Overall, the purpose of this review is to identify resistance mechanisms that offer improved resilience of Eucalyptus plantations in the face of increasing threats by foliar fungal pathogens. The broad aim is to promote sustainable forestry through appropriate selection of resistance traits in trees that are widely planted for commercial timber production.

Recent findings

Eucalyptus is among the most important tree genera planted for commercial timber production worldwide. Numerous foliar pathogens have been reported on these trees in the last 30 years with numbers of recent reports increasing exponentially. The majority of these diseases affect the leaves and shoots of the trees. Knowledge on resistance traits in Eucalyptus to fungal foliar pathogens is limited. This is in part due to the high intra- and inter-species variation in molecular and physiological responses of the host and variation in responses to different pathogens, especially those with different trophic modes. A well-founded understanding of such host responses will provide valuable knowledge required to maintain healthy, sustainable Eucalyptus plantations, especially in the face of changing environmental conditions, where new diseases are caused by fungi previously not considered relevant.

Summary

Foliar diseases are among the most important challenges for Eucalyptus plantations globally. The effects of climate change and new or more serious outbreaks present an important threat to the sustainability of Eucalyptus plantations worldwide. Due to restrictions on the use of chemicals, more feasible solutions for disease management lie in selecting planting material with resistance traits. To achieve that goal, it is essential to understand the most important physiological and molecular responses of Eucalyptus to infection by pathogens that infect their foliar tissues. In this review we summarise the available knowledge of the main physiological defence barriers and genetic traits that play key roles in the broad defence against foliar fungal pathogens. Furthermore, we consider defence pathways that are specifically related to the lifestyle and trophic mode of the pathogens. In order to ensure the future sustainability of Eucalyptus plantations, it will be necessary to understand how disease resistance is affected by climate change, as well as the adaptability of the hosts and pathogens to newly emerging environmental conditions.