Cl Mohammed

Induced resistance to pests and pathogens in trees

Tree resistance can be enhanced by a variety of biotic and abiotic inducers, including nonpathogenic and pathogenic microbes, and herbivores, resulting in enhanced protection against further biotic injury. Induced resistance (IR) could be a valuable tool in sustainable pest management. IR has been actively studied in herbaceous plant species, and, in recent years, in woody plant species, and is fast emerging as an intriguing, eco-friendly concept for enhancing tree resistance. However, before application of IR becomes possible, there is a need to increase our knowledge of the mechanisms of defence in forest trees. A richer understanding of these phenomena will play a critical role in developing sustainable integrated pest management strategies. This review summarizes our current knowledge of IR in forest trees, focusing on inducible defence mechanisms, systemic induction of resistance and phytohormone signalling networks. We conclude by discussing the potential advantages and limitations of applying IR-based management tools in forest systems.

Puccinia psidii: a threat to the Australian environment and economy a review

Puccinia psidii causes a rust disease on a broad range of hosts in the Myrtaceae and Heteropyxidaceae. It is native to South America where it can cause severe disease in eucalypt plantations and other introduced Myrtaceae. The pathogen has recently expanded its geographical range to Hawaii, increasing concerns about the potential for an incursion in Australia. This paper reviews the taxonomy, biology, impact and options for control of P. psidii. It also discusses the probable impact if an incursion were to occur in Australia and the preparations that must be made to mitigate adverse consequences.

Shifts in biomass and resource allocation patterns following defoliation in Eucalyptus globulus growing with varying water and nutrient supplies.

In woody species, potential mechanisms to compensate for tissue loss to herbivory and diseases have been related to post-event shifts in growth, biomass and internal resource allocation patterns, as modulated by external resource limitations. We examined the interactive effects of belowground resource limitations by varying nutrient and water availability, and aboveground carbon limitation imposed by a single defoliation event (40% leaf removal) on stem growth, whole-tree and within-tree resource allocation patterns (total non-structural carbohydrate and nitrogen) and below- and aboveground biomass allocation patterns in 8-month-old, field-grown Eucalyptus globulus Labill. saplings. Two months after treatments were imposed, the direction of the stem growth response to defoliation depended on the abiotic treatment. Five months after defoliation, however, we found little evidence that resource availability constrained the expression of tolerance to defoliation. With the exception of the combined low-nutrient and low-water supply treatment, saplings grown with (1) adequate water and nutrient supplies and even with (2) low-water supply or (3) low-nutrient supply were able to compensate for the 40% foliage loss. The observed compensatory responses were attributed to the activation of several short- and longer-term physiological mechanisms including reduced biomass allocation to coarse roots, mobilization of carbohydrate reserves, robust internal N dynamics and increased ratio of foliage to wood dry mass.

Variation in the ITS and IGS regions of ribosomal DNA among the biological species of European Armillaria

Variation within the internal transcribed spacer (ITS) and the intergenic spacer (IGS) of the ribosomal RNA gene of isolates representing seven European species of Armillaria was examined by PCR, coupled with RFLP analysis and partial sequencing of the ITS region.

Genetic variation in Eucalyptus globulus for susceptibility to Mycosphaerella nubilosa and its association with tree growth

Mycosphaerella species are fungal leaf pathogens of Eucalyptus globulus, one of the major plantation tree species in temperate regions of the world. We examined the quantitative genetic variation in susceptibility to infection by Mycosphaerella nubilosa in a genetically diverse population ofE. globulus families growing in a field trial in north-west Tasmania. Disease incidence and severity were assessed on juvenile foliage following a heavy epidemic where mean leaf area damage was 34%. Disease incidence was uniform across the trial. Significant genetic variation for susceptibility was detected with a narrow sense heritability of disease severity being the highest yet reported (h2=0.60) for aMycosphaerella disease of eucalypts. M. nubilosa damage had a significant deleterious effect on tree growth at both the phenotypic and genetic level. We suggest that E. globulus has at least two mechanisms involved in avoiding the deleterious effects of this disease, one is through resistance of the juvenile foliage per se and the other is through the ontogenetic switch to the resistant adult foliage. There is ample opportunity to select genotypes ofE. globulus that are relatively resistant to damage and if these are deployed in areas of high disease risk, significant benefits in plantation productivity could be obtained.

Comparison of Antifungal and Antioxidant Activities of Acacia mangium and A. auriculiformis Heartwood Extracts

The effect of heartwood extracts from Acacia mangium (heartrot-susceptible) and A. auriculiformis (heartrot-resistant) was examined on the growth of wood rotting fungi with in vitro assays. A. auriculiformis heartwood extracts had higher antifungal activity than A. mangium. The compounds 3,4′,7,8-tetrahydroxyflavanone and teracacidin (the most abundant flavonoids in both species) showed antifungal activity. A. auriculiformis contained higher levels of these flavonoids (3.5- and 43-fold higher, respectively) than A. mangium. This suggests that higher levels of these compounds may contribute to heartrot resistance. Furthermore, both flavonoids had strong 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity and laccase inhibition. This suggests that the antifungal mechanism of these compounds may involve inhibition of fungal growth by quenching of free radicals produced by the extracellular fungal enzyme laccase.

Crown-scale evaluation of spectral indices for defoliated and discoloured eucalypts

Remote sensing for evaluation of canopy health in plantation eucalypts is a realistic option for forest managers in the near future if reliable and robust methods of spectral analysis can be developed. Pot‐grown eucalypts of three species important to the Australian plantation industry were used for crown‐scale spectral (400–1000 nm) evaluations of vegetation indices as indicators of common symptoms of stress. When defoliation treatments (in E. globulus) or exposure to cold and nutrient deprivation (in E. pilularis) resulted in large differences in leaf cover, the red edge position and slope indices, two normalized difference vegetation indices (NDVIs), modified chlorophyll absorption ratio index 2 (MCARI2) or modified triangular vegetation index 2 (MTVI2) were most strongly correlated to leaf cover. However the NDVIs were significantly affected by soil background in a study with E. globulus. The percentage of red leaves resulting from stress treatment was most strongly correlated with the anthocyanin reflectance index (ARI) and red‐green index (RGI) in both E. grandis and E. pilularis, however the RGI was affected by background type in the E. globulus study while the ARI was not. Exposure to cold and nutrient deprivation led to marked changes in leaf cover for E. pilularis but not in E. grandis and a much more reduced level of chlorophyll in E. pilularis than is suspected in E. grandis. In E. globulus, defoliation from the upper crown was easier to detect with spectral data than from the lower crown. Results were generally comparable to studies of eucalypt crown condition from native forests.

New foliar pathogens of Eucalyptus from Australia and Indonesia

Mycosphaerella tasmaniensis is newly described from Mycosphaerella leaf blotch symptoms occurring on Eucalyptus nitens in Tasmania, Australia. Single ascospore cultures produced a Mycovellosiella anamorph, described here as M. tasmaniensis. Both states occurred together, as well as separately on leaf spots. Phaeophleospora epicoccoides (= Kirramyces epicoccoides) is commonly associated with leaf spots of Eucalyptus spp. in Australia. The teleomorph, Mycosphaerella suttoniae, previously known only from Indonesia, was also collected on E. grandis leaves from Australia. A Cylindrocladium leaf blight disease of young E. grandis trees in Indonesia was found to be associated with a new species of Calonectria. Calonectria multiseptata and its anamorph Cylindrocladium multiseptatum is newly described and distinguished from other species based on their larger, multi-septate ascospores and conidia.

Development of nested polymerase chain reaction detection of Mycosphaerella spp. and its application to the study of leaf disease in Eucalyptus plantations

ABSTRACT Mycosphaerella leaf disease (MLD) is a serious disease of two of the major eucalypt species grown in temperate regions worldwide, Eucalyptus globulus and E. nitens. More than 30 species of Mycosphaerella have been reported on eucalypts worldwide. Accurate, rapid, and early discrimination of Mycosphaerella spp. causing crown damage to E. globulus and E. nitens will assist the development of sustainable management strategies. This study describes the development, and incorporation in a nested polymerase chain reaction (PCR) approach, of specific primers for the detection and identification of Mycosphaerella spp. commonly reported from leaf lesions of E. globulus and E. nitens in Australia. Primer design was assisted by sequence alignment and phylogenetic analysis of 165 nonredundant sequences from the nuclear ribosomal DNA internal transcribed spacer regions of Mycosphaerella and related species. Phylo-genetic analysis revealed very high sequence similarity for two taxon groups, Mycosphaerella grandis and M. parva, and M. vespa, M. ambi phylla, and M. molleriana, and primers were designed to differentiate each of the two groups. Three other species, M. cryptica, M. nubilosa, and M. tasmaniensis, were distinct and distinguished by species-specific primers. In double-blind trials, the detection test accurately and rapidly identified Mycosphaerella spp. in cultures and discriminated against other pathogens that co-occur in or on Eucalyptus leaves, thereby verifying its reliability. The detection test has an internal amplification control in the first-round PCR with fungal-specific primers to raise confidence in test results, particularly to highlight negative results due to PCR inhibition. When applied to DNA extracted from leaf or stem samples either as multiple or single lesions, it detected and identified up to five Mycosphaerella spp. or taxon groups in both positively identified and in young (putative) MLD lesions. The samples were 20 mm(2) or larger in surface area and were collected while undertaking disease rating assessments in an experimental investigation of Eucalyptus plantations and regrowth forest. Using nested PCR detection, Mycosphaerella spp. were positively identified in 2 days, 1 to 5 months earlier than by classical methods, demonstrating the potential application of this detection test to the early discrimination of MLD components in ecological, epidemiological, and genetic investigations.

Do artificial and natural defoliation have similar effects on physiology of Eucalyptus globulus Labill. seedlings

Abstract• Artificial defoliation is often used to simulate defoliation by herbivory and is usually considered a good indication of a plant’s response to a given type of damage. However, the findings of studies directly comparing the two defoliation types are inconsistent.• Here, the short term effects of artificial and insect defoliation by larvae of Paropsisterna agricola on growth, biomass allocation and photosynthetic capacity of Eucalyptus globulus seedlings were compared in a glasshouse experiment. The artificial defoliation was carried out to closely resemble the spatial patterns observed for insect defoliation.• Height and diameter increments were reduced as a result of insect defoliation, whereas artificial defoliation had no significant effect on height. Increased photosynthetic capacity was observed in response to both treatments, but the magnitude of this increase was larger in insect-than in artificially-defoliated seedlings. Significant reductions in foliar carbohydrate content and total biomass were noticeable in artificially-defoliated seedlings. Although the foliar carbohydrate levels also decreased across the crown zones following insect defoliation treatment, seedlings allocated a large amount of their biomass in the branches of the damaged zone.• Despite our best endeavours to simulate insect defoliation in the artificial treatment, the latter may not reflect accurately the full strength of the effects. However, artificial and insect defoliation were similar in their direction of the responses they caused in E. globulus seedlings.Résumé• La défoliation artificielle est couramment employée pour simuler la défoliation par les insectes herbivores et elle est généralement considérée comme un bon indicateur de la réponse des plantes pour un type de dommage donné. Cependant, les résultats d’études comparant directement les deux types de défoliation sont inconsistants.• Ici, les effets court terme des défoliations artificielles et naturelles par la larve de Paropsisterna agricola ont été comparés au plan de la croissance, de l’allocation de la biomasse et de la capacité de photosynthèse dans une expérimentation conduite en serre. La défoliation artificielle a été menée pour ressembler étroitement aux modèles spatiaux observés avec la défoliation par les insectes.• À la suite de la défoliation par les insectes, les accroissements en hauteur et en diamètre ont été réduits, alors que la défoliation artificielle n’a eu aucun effet significatif sur la hauteur. L’augmentation de la capacité de photosynthèse a été observée en réponses aux deux traitements, mais l’ampleur de cette augmentation a été plus forte pour les plants défoliés par les insectes que pour les plants artificiellement défoliés. Des réductions significatives de la teneur foliaire en glucides et de la biomasse totale ont été notées chez les plants artificiellement défoliés. Malgré la réduction générale de la teneur en glucides à la suite de la défoliation par les insectes, les jeunes plants assignèrent une importante partie de la biomasse aux branches de la zone endommagée.• Malgré nos meilleures tentatives pour simuler la défoliation par les insectes dans le traitement artificiel, ce dernier ne reflète pas avec exactitude toute l’ampleur de l’impact engendré. Cependant, les défoliations artificielles et naturelles ont entraîné chez les jeunes plants d’E. globulus des réponses qui allaient dans le même sens.