Resistance screening to fungal diseases for plantation eucalypts in Vietnam : molecular tools to assist fungal detection and identification
Creators: name: Tran Thanh, T
Publisher: name: University Of Tasmania
Year: 2023

description: Eucalyptus species are a significant component of the total forest plantation estate in Vietnam (23.6% in 2005). Fungal diseases have had a marked impact on eucalypt productivity and the area of plantation under Eucalyptus has halved over the last decade. Breeding programs have been implemented to address the problem of disease and have focused on the selection of species or clonal lines which have both high yield and disease resistance. This thesis describes the resistance screening carried out in three clonal eucalypt trials planted in southern Vietnam. Sixty eucalypt clones and one seedlot (a landrace as a control) were assessed for growth traits, survival and crown damage. Approximately 50% of the clones, including the control, were classed as poorly performing clones based on the various criteria. Seventeen clones were significantly susceptible to disease at one or more sites. The limited number of clones ranked as top performers were those that were fast growing, with a high survival rate and resistance to disease. Coniella leaf spot was prevalent but was not systematically associated with high levels of damage. The more damaging pathogens present were Cryptosporiopsis eucalypti, Cylindrocladium quinqueseptatum, Kirramyces destructans. Microsphaeropsis globulosa on eucalypts was recorded for the first time on Eucalyptus in Vietnam. Although the major fungal pathogens are usually easily recognisable there are ambiguities in identification in the field. Future resistance screening and associated epidemiological studies will benefit from molecular techniques to detect and identify fungi, especially methods that can be applied directly to plant tissue. Due to quarantine issues it was not possible to develop molecular tools to detect and identify fungal pathogens using infected tissue collected from the clonal eucalypt trials in Vietnam. Methodologies for subsequent use in Vietnam were developed using locally available material in Tasmania, within the context of an ongoing ecological investigation of the wood decay fungi associated with the logs of Eucalyptus obliqua in the wet sclerophyll forests of southern Tasmania. Before attempting to identify fungi directly from fragments of decayed log, a reference library of ITS sequences was established from the DNA analysis of 111 sporocarps and 93 wood decay ,isolates obtained from a previous study (which had been grouped according to morphology). An additional 70 fungal cultures were obtained from the 111 sporocarps collected in the study. Sporocarps were morphologically identified to a genus or species level or had been given a tag name while awaiting formal identification. rDNA was amplified from DNA extracted from sporocarp tissue and fungal cultures. The internal transcribed spacer (ITS) region of the rDNA was sequenced. DNA was extracted from fragments of rotted wood from E. obliqua logs and the rDNA ITS amplified with fungal specific primers. The PCR products were cloned before sequencing as multiple fungal species were present in most samples. Clones were screened by PCR-RFLP and representatives of each PCR-RFLP group were sequenced. To identify the fungi present in the rotted wood samples, sequences were compared to those from public and private databases, including the reference database set up within this study. The advantages and problems associated with identifying fungi directly from plant tissue using molecular techniques and the relevance of such methodology to resistance screening in Vietnam is discussed.