Health and nutrition of plantation eucalypts in Asia

Understanding site fertility constraints has lifted productivity of eucalypt plantations in East and South-east Asia through targeted application of inorganic fertilisers. Whilst most attention has been given to the supply of nitrogen and phosphorus in silvicultural prescriptions, and inoculation with mycorrhizal fungi is being undertaken by some companies, more attention is required to diagnose and correct micronutrient disorders. For example, the incidence of boron deficiency remains a concern across the region affecting tree growth, tree form, fibre quality and possibly the extent of damage from some eucalypt pathogens. As even mild deficiencies of micronutrients such as copper, boron and manganese can alter the phenol pathway, limitations in the uptake of these elements have implications for tree defence against some fungal pathogens. Due to the high humidity and temperatures throughout the year, fungal leaf diseases such as Cylindrocladium quinqueseptatum have had a huge impact on the eucalypt plantation industry in South-east Asia. Often poor nutrition seems to be an underlying cause in disease susceptibility. However, in spite of the size of the eucalypt plantation sector, there is not an integrated understanding of biotic and abiotic causes and their interactions by the industry. Furthermore, the emergence of new eucalypt pathogens such as Kirramyces destructans and their rapid spread threatens the viability of plantations unless selection of resistant clones and breeding for resistance can keep up with the incursion of new and invasive eucalypt pathogens. In a number of countries, there is low genetic diversity in eucalypt plantations and breeding programs are yet to embrace screening for disease resistance. The challenge to a successful eucalypt plantation industry in Asia is to optimise genetics and nutrition in order to produce trees with the greatest chance of overcoming pest and disease threats.