Eucalyptus Genotypes Research Articles

Using seasonal physiological and biochemical responses to select forest components adapted to soybean and corn intercropping

Given the increasing utilization of forest components in integration systems worldwide, coupled with the growing demand for food in regions facing water restrictions, this study aims to evaluate how physiological and biochemical parameters contribute to the diversification of adaptive mechanisms among native species and eucalyptus genotypes intercropped with soybean or corn. The native tree species Anadenanthera macrocarpa and Dipteryx alata, and the eucalyptus genotypes Urograndis I-144 and Urocam VM01, were grown in soybean and corn intercropping areas and evaluated in fall, winter, spring, and summer. The study evaluated morning water potential, chloroplast pigment concentration, gas exchange, cell damage, and antioxidant enzyme activity. Intercropped with soybean, development the of A. macrocarpa improved through instantaneous water use efficiency, energy use by the electron transport chain, chloroplast pigments, and catalase enzyme activity. On the other hand, A. macrocarpa when, intercropped with corn, despite increasing energy absorption by the reaction center, there is a need for non-photochemical dissipation and in the activity of the enzymes superoxide dismutase and ascorbate peroxidase in response to water and oxidative deficits. In D. alata, the physiological and biochemical responses were not influenced by intercropping but by seasons, with increased chloroplast pigments in fall and electron transport in summer. However, in corn intercropping, the dissipation of excess energy allowed leaf acclimatization. The I-144 and VM01 genotypes also showed no significant differences between intercrops. The results describe photosynthetic and biochemical challenges in the native species A. macrocarpa intercropped with corn, such as a greater need for enzymatic and non-enzymatic defense mechanisms in response to more negative water potential. In D. alata, the challenges are present in both intercrops due to improved mechanisms to protect the photosynthetic apparatus. The survival of the I-144 genotype may be inefficient in both intercrops under prolonged drought conditions, as it modifies the photosystem; in contrast, genotype VM01 was the most adapted to the system for using captured energy, reducing water loss and being resilient.

Standard area diagrams for severity assessment of eucalypt bacterial leaf blight caused by Xanthomonas spp.

AbstractBacterial leaf blight (BLB) caused by Xanthomonas spp. is an important threat for eucalypt production. Planting of resistant genotypes is the best strategy for eucalypt BLB control. However, selection of resistant clones is challenging since the disease is caused by at least three Xanthomonas species that can be sympatric and cause a range of foliar symptoms. So far, standard area diagrams (SADs) to assess eucalypt BLB severity caused by different Xanthomonas species have not been reported. Here, SADs for eucalypt BLB severity assessment were developed. Plants of five eucalypt genotypes were individually inoculated with different Xanthomonas species and leaves exhibiting lesions varying in colour, shape, and size were digitally scanned for disease assessment. Among 150 scanned leaves, the actual leaf affected area ranged from 0.01% to 55%. Based on these minimum and maximum values and the frequency of severity distribution, the 10 leaves that best represented the distribution of affected leaf area were selected to assemble the SADs. Groups of experienced and inexperienced raters estimated BLB severity on a subset of 50 out of the 150 original leaves without and then with the use of the SADs. Correlation concordance analyses revealed that SADs provided a significant improvement in accuracy, precision and reliability of disease estimates by both rater groups, with higher gains observed for the inexperienced group. The SADs developed in this study will be useful for selection of eucalypt genotypes resistant to BLB under controlled conditions when knowledge on the Xanthomonas species composition is lacking or when local populations are comprised of several species.

Fine Root Density Dynamics and Carbon Stock of Eucalyptus spp.: Interplay of Age, Genotype, and Edaphoclimatic Conditions.

Roots play a fundamental role in forest ecosystems, but obtaining samples from deep layers remains a challenging process due to the methodological and financial efforts required. In our quest to understand the dynamics of Eucalyptus roots, we raise three fundamental questions. First, we inquire about the average extent of the roots of two contrasting Eucalyptus genotypes. Next, we explore the factors that directly influence the growth and depth of these roots, addressing elements such as soil type, climate, and water availability. Lastly, we investigate how the variation in Eucalyptus species may impact root growth patterns, biomass, and carbon stock. In this study, we observed that the maximum root depth increased by an average of 20% when genotypes were grown on sites with higher water availability (wet site). E. urophylla stands had a higher biomass and carbon stock (5.7 Mg C ha-1) of fine roots when cultivated on dry sites (annual rainfall~727 mm) than the wet sites (annual rainfall~1590 mm). In E. grandis × E. camaldulensis stands, no significant differences were observed in the stock of fine root biomass (3.2 Mg C ha-1) between the studied environments. Our results demonstrated that genotypes with greater drought tolerance (E. grandis × E. camaldulensis) tend to maintain higher stocks of fine root biomass (3.2-6.3 Mg ha-1) compared to those classified as plastic (E. urophylla), regardless of the edaphoclimatic conditions of the cultivation site. Finally, our research helps understand how Eucalyptus trees adapt to their environment, aiding sustainable forest management and climate change mitigation. We also provide a practical tool to estimate underground biomass, assisting forest managers and policymakers in ensuring long-term forest sustainability.

Chemical composition of the essential oil of Eucalyptus genotypes susceptible or resistant to the gall-forming wasp Leptocybe invasa Fisher & La-Salle, 2004 (Hymenoptera: Eulophidae)

Eucalyptus are trees native to Australia and have been cultivated in various regions of the world. In its worldwide expansion, several native and exotic insects began to use these plants for their survival. Leptocybe invasa Fisher & La-Salle, 2004 (Hymenoptera: Eulophidae) is a gall wasp that lay eggs into leaves, young branches, and petioles causing galls; however, there are resistant and susceptible eucalyptus genotypes to gall formation. This study aimed to compare the chemical composition of eucalyptus genotypes and relate it to resistance and susceptibility to gall formation. Leaf oils were extracted by steam distillation and oil compositions were analyzed. The essential oils of eucalyptus genotypes resistant to gall formation had 12 constituents, which do not occur in susceptible genotypes, probably one of the factors that contributes to the resistance of these plants to gall formation. Thus, we suggest an early evaluation of resistant or susceptible eucalyptus genotypes, based on the chemical composition of the essential oils of these plants, avoiding economic losses of planting susceptible genotypes.

Selection of eucalyptus genotypes for charcoal production based on using multivariate analysis

the selection of Eucalyptus genotypes appropriate for charcoal production depends on both assessing wood features and correlations among them. However, the large number of variables of wood and charcoal makes interpretation complex; thus, it is necessary using statistical techniques to analyze the cluster of variables that influence each sampling element, simultaneously. In addition, the high cost and long time required to set wood and charcoal properties makes it unfeasible to feature a large number of genotypes within a short period-of-time. Accordingly, the aims of the present study are to develop a pre-selection methodology and to recommend Eucalyptus genotypes for charcoal production, based on using cluster multivariate statistics. In total, 64 Eucalyptus genotypes from a clonal database were used in the study; their wood basic density, volume and dry mass per hectare were determined, as well as their heartwood/sapwood ratio. These parameters were used in the pre-selection procedure, which combined classification based on median, variables’ individual rank, and Mulamba and Mock selection index. The determination of properties presented by wood and charcoal belonging to the pre-selected genotypes was carried out, and they were used as input variables for clustering analysis based on the Tocher method and on Unweighted Pair Group Method with Arithmetic Mean (UPGMA). The pre-classification methodology was efficient, because it allowed selecting 16 genotypes showing the desired values for the four features used in the pre-selection process. Overall, the properties of wood and charcoal belonging to the pre-selected genotypes were considered satisfactory to be used in steel production. The clustering methods were effective in solving genotype classification issues. Tocher optimization method application was much more practical, because it led to the optimum number of clusters without the need of researcher’s intervention, besides the fact that clusters’ compliance was similar to that assessed through the UPGMA method. It was possible concluding that genotype numbers 1954, 1453, 1923 and 4296 are the most recommended ones for charcoal production, according to the herein used analysis techniques, based on the study of mean values recorded the features of wood and charcoal in each cluster.

Wood Basic Density Assessment of Eucalyptus Genotypes Growing under Contrasting Water Availability Conditions

Limited research exists on wood properties in E. nitens × E. globulus hybrid genotypes grown in water-limited conditions generated by the climate change influence in Mediterranean areas. The EUCAHYDRO project aimed to assess environmental stress impacts on eucalyptus genotypes, including responses to reduced water availability, and to evaluate wood density and resistance using the non-destructive drill resistance technique. This study focused on 10-year-old E. nitens × E. globulus hybrids and Eucalyptus badjensis Beuzev. & Welch, revealing that low irrigation led to a 13% (p < 0.05) decrease in diameter and a 6.5% (p > 0.05) increase in wood density for the hybrids. On the contrary, E. badjensis demonstrated a noteworthy 22% increase in wood density (p < 0.05), while showing a corresponding 0.6% growth increase (p > 0.05), as measured by the diameter at breast height. Drill resistance measurement results indicated that E. nitens × E. globulus’ amplitude ranged from 20.1% to 26.6%, while E. badjensis’ ranged from 20.8% to 27.2%. The study revealed a high correlation between resistance amplitude and wood density, with coefficients of 0.97 observed for E. nitens × E. globulus and 0.84 for E. badjensis (p < 0.05). These findings fall within the range reported in similar studies involving Eucalyptus spp. The primary focus of the research was to assess the growth potential and wood quality of novel Eucalyptus spp. under conditions of water limitation. The study also explored the utility of drill resistance as a predictive measure for evaluating wood density as an indicator of wood quality.

Insights into Leptocybe invasa resistance in Eucalyptus: phenotyping, genotyping and in silico approaches.

The gall wasp, Leptocybe invasa, poses a significant global threat to Eucalyptus cultivation, by causing substantial economic losses. The objective of this study was to differentiate between resistant and susceptible genotypes by morphological characteristics using image analysis based on the damage caused by the gall wasp. In addition, consensus sequences derived from transposable elements (TEs) and the genome of Eucalyptus spp. Were identified by in silico analysis. Furthermore, another objective was to discriminate Eucalyptus genotypes in response to Leptocybe invasa by conducting molecular analyses involving transposable elements and inter simple sequence markers. For image analysis, the GroundEye ® system was used to collect images of 60 leaves from six genotypes, three of which were resistant and three susceptible. Eucalyptus spp. sequences were obtained from the GenBank database by in silico analysis and pairwise alignments with TE sequences were conducted using BLASTN. Multiple sequence alignment was performed with Clustal Omega, followed by the identification of conserved regions in Jalview. A motif signature was generated using Weblogo. For molecular characterization using ISSR markers and TEs, samples of young leaves were obtained from a total of 80 Eucalyptus seedlings, of which 50 were classified as resistant and 30 as susceptible to L. invasa. It was possible to distinguish gall wasp susceptible and resistant genotypes by image analysis. In silico analysis enabled the identification of conserved regions in the Eucalyptus spp. genome, which were associated with proteins involved in secondary metabolite production, e.g., terpenes, which play a role in the response to L. invasa. The discrimination capacity of TEs and ISSR primers was demonstrated and bands were generated that could be used to identify resistant genotypes. However, increasing the number of markers required to discriminate genotypes in both cases is suggested.

Key traits influencing the resistance of Eucalyptus camaldulensis to wind damage in coastal areas of South China.

China is one of the countries in the world most seriously affected by typhoons, which pose a great threat to the eucalyptus plantation industry. However, few studies have comprehensively accounted for the impact of key traits on the wind damage/resistance of eucalyptus. To identify the key factors affecting the wind resistance of eucalyptus, 20 eucalyptus genotypes were selected; a total of 18 traits, including the wind damage index, growth traits, and wood traits, were measured, and the wind resistance was determined via the tree-pulling test. Correlation, principal component, canonical correlation, and path analyses were performed to evaluate these traits. Correlation analysis revealed that the wind resistance of eucalyptus plants was related to the tree height, volume, and duration of stress wave propagation. Principal components and tree-pulling variables were further used for correlation and path analyses. Canonical correlation analysis and the PA-OV model showed that holocellulose and lignin contents and fiber width, as well as growth traits, were important factors affecting the stability of standing trees under typhoon conditions. The key traits influencing the wind resistance of Eucalyptus camaldulensis, which may provide a reference for evaluating the wind resistance of Eucalyptus varieties for forest management, were identified. This study provides a knowledge base for forest management and planning in typhoon-prone coastal areas, and provides a theoretical basis for the breeding and genetically improving eucalyptus stocks based on wind resistance characteristics.

Endophytic Development of the Entomopathogenic Fungus Beauveria bassiana Reduced the Development of Galls and Adult Emergence of Leptocybe invasa in Susceptible Eucalyptus

Eucalyptus cultivation in arid regions is limited by the losses caused by the galling wasp, Leptocybe invasa Fisher and La Salle, 2004 (Hymenoptera: Eulophidae); it oviposits below the epidermis of the central veins, mainly on seedlings in nurseries and/or young plants in the field, causing galls where the insects develop. Galls modify the normal circulation of sap in vascular tissues, ultimately affecting the development of infested plants and resulting in slower growth. Eucalyptus genotypes tolerant to water stress are susceptible to L. invasa, and this pest has no effective control methods. Here, we aimed to (i) determine the initial infestation dynamics of L. invasa in Eucalyptus plants inoculated with Beauveria bassiana and (ii) identify any change in the development of galls. B. bassiana-inoculated seedlings were infested with L. invasa. Susceptible plants were unaffected, and gall development was negatively affected at multiple stages. A fungal solution containing B. bassiana reduced gall development and the emergence of L. invasa adults in eucalyptus plants at considerable rates. The total number of adult emergence holes was 89.74% fewer for inoculated plants when compared to uninoculated plants. These results can help develop B. bassiana products to control L. invasa in susceptible eucalyptus plants for improved, sustainable forestry.

Screening of Eucalyptus camaldulensis clones for enhancing productivity and sustainability in problematic soils of Southern India

Among the various challenges faced by eucalyptus plantations in the Indian pulp industry, one of them is the development of resilient clones adaptable to saline soils. Large genetic diversity exists in E. camaldulensis because of high out-crossing rates and is expected to pass traits into the new developed clones. We used a salt injury score, survival percentage and proline content as a screening criterion to select new clones tolerant to high salt levels in soils. Proline has been identified as a beneficial solute in plants under stress caused by high salinity. Three months old clones of eleven new eucalyptus genotypes were transplanted in pots with free-draining coarse river sand. Four treatments comprising control, high Salt, High Salt + High pH and High pH were arranged in a randomised block design. Common salt (NaCl) was used for regulating salt concentrations while sodium bicarbonate (NaHCO3) was used for regulating the pH of the solutions. NaCl concentrations were increased every third day until the final concentration of 150 mM was reached. Similarly, pH of the solutions was also gradually increased till final pH of 10 was attained. Each treatment solution was delivered through automated drip delivery. Salt injury scores based on symptoms were positively correlated (0.812) with survival percentage and proline content. Eucalyptus genotypes were classified into five salt tolerant groups: tolerant (T), moderately tolerant (MT), moderately sensitive (MS), sensitive (S), and highly sensitive (HS). The mean values of proline content in leaves were different among the five groups, indicating that the proline content is a reliable marker for identifying salt tolerance. Proline contents in stressed seedlings were significantly different between the tolerant and highly sensitive groups, but the difference among the intermediate groups (MT, MS and S) was not significant. As the stress levels of salt and pH were increased, the sensitive hybrid clone tested showed very poor growth, which was also negatively correlated with the proline content in its leaves. Combination of high salt and high pH was also found to be correlated with reduced proline content, poor growth and survival among sensitive genotypes. In addition to the commonly used sodium and pH induced symptoms, proline content is suggested to be another useful criterion to differentiate salt-tolerant from salt-sensitive genotypes. This study helped in classification of genotypes with different levels of salt and pH tolerance, which may be used for deployment of genotypes according to changing edaphic conditions for sustainability of eucalyptus plantations.

Quambalaria eucalypti found on Eucalyptus in Indonesia

AbstractThe Eucalyptus plantation industry in Indonesia has expanded rapidly during the last few decades. During routine nursery disease surveys, symptoms of a leaf and shoot blight disease were detected on Eucalyptus mother plants. Isolates were obtained from symptomatic tissues and identified using DNA sequence analyses. Phylogenetic analyses showed that the isolates were those of Quambalaria eucalypti. Pathogenicity tests were conducted with isolates of Q. eucalypti on clones of E. pellita and E. grandis × E. pellita hybrids. These resulted in symptoms similar to those observed on naturally infected plants. Eucalyptus genotypes tested showed variation in their susceptibility, highlighting the potential to select and breed for resistance and thus to manage future outbreaks of the disease. This is the first report of the pathogen in Indonesia as well as in Southeast Asia.

Phylogeny, Morphology, Distribution, and Pathogenicity of Seven Calonectria Species from Leaf Blighted Eucalyptus in HaiNan Island, China.

Leaf blight caused by Calonectria species is a major constraint to Eucalyptus trees in China. Calonectria leaf disease on Eucalyptus planted in China was first reported in HaiNan Island in 1985. No systematic investigation or identification of Calonectria species associated with diseased Eucalyptus in HaiNan Island have been performed to date. In order to comprehensively understand the species diversity, distribution, and pathogenicity of Calonectria associated with diseased Eucalyptus trees in HaiNan Island, 400 Calonectria isolates were obtained from 278 diseased Eucalyptus trees planted in 17 sites in five counties/regions. All 400 isolates were identified based on DNA sequence comparisons of the translation elongation factor 1-alpha (tef1), β-tubulin (tub2), calmodulin (cmdA), and histone H3 (his3) gene regions as well as a combination of morphological characteristics. Seven species, namely C. acaciicola (198 isolates, 49.5%), C. pseudoreteaudii (161 isolates, 40.25%), C. reteaudii (29 isolates, 7.25%), C. hawksworthii (6 isolates, 1.5%), C. hongkongensis (4 isolates, 1%), C. auriculiformis (1 isolate, 0.25%) and C. chinensis (1 isolate, 0.25%), were identified. This is the first report of C. acaciicola in China. Calonectria acaciicola, C. pseudoreteaudii, and C. reteaudii belong to the C. reteaudii species complex and were the dominant species collected, accounting for 97% of all the isolates obtained. Overlap in vesicle shape, macroconidia size, and macroconidia septa number existed among these three species in the C. reteaudii species complex. The geographical regions significantly influenced the distribution of C. acaciicola and C. pseudoreteaudii. Representative isolates of C. acaciicola, C. pseudoreteaudii, C. reteaudii and C. hawksworthii produced abundant macroconidia were used in conidial suspension inoculation on Eucalyptus seedlings. Inoculation showed that all four of the tested Calonectria species were highly pathogenic to the two tested Eucalyptus genotypes. The tolerances of two Eucalyptus genotypes were significantly different. This study conducted the first systematic investigation and identification of Calonectria species associated with Eucalyptus leaf blight in HaiNan Island and advanced the concept of selection of disease resistant Eucalyptus genotypes for managing Eucalyptus leaf blight caused by Calonectria species in China.

Susceptibility of Eucalyptus trees to defoliation by the Eucalyptus snout beetle, Gonipterus sp. n. 2, is enhanced by high foliar contents of 1,8-cineole, oxalic acidand sucrose and low contents of palmitic and shikimic acid.

Gonipterus sp. n. 2 (Coleoptera, Curculionidae) is an invasive, commercially important weevil that causes large-scale defoliation of Eucalyptus trees. The weevil specifically feeds on young leaves and new shoots, thus reducing tree growth. The weevil displays a very strong preference for certain Eucalyptus genotypes, however, this behaviour and the chemistry underlying it is poorly understood, thereby complicating the selection of resistant trees. To elucidate the feeding preference of Gonipterus sp. n. 2, we assessed the relative levels of susceptibility of 62 Eucalyptus genotypes from 23 species using a laboratory choice assay. This revealed large intraspecific variation in susceptibility to weevil feeding, which for certain species, exceeded the interspecific variation. A semiquantitative metabolite profile analysis on 13 genotypes revealed strong correlations of 10 metabolites to feeding damage. The behavioural effects of the identified compounds were assessed through an in vitro feeding preference assay using artificial diets as well as under field conditions. This revealed three phagostimulants (1,8-cineole, oxalic acidand sucrose) and two feeding deterrent compounds (shikimic acid and palmitic acid) for Gonipterus sp. n. 2. These chemical markers can be applied to tree breeding programmes for the selection of resistant genotypes to reduce damage caused by Gonipterus weevils.

Correlating Eucalyptus leaf metabolomics with preference of the bronze bug, Thaumastocoris peregrinus.

Eucalyptus species are among the most planted trees in forestry production, an ever-increasing commercial activity worldwide. Forestry expansion demands a continuous search for preventive and sanitary measures against pests and diseases. Massive application of phytosanitary products is incompatible with the forestry sector, so forest health management must be based on other principles. In this context, studies on insect plant relationships mediated by plant metabolites may contribute information relevant to plant resistance and genotype selection. In this study, we analyzed the leaf metabolome of four Eucalyptus species commonly planted in southern South America, to correlate this chemical information with feeding preference of Thaumastocoris peregrinus (Hemiptera: Thaumastocoridae), an important pest of eucalypt plantations. Gas chromatography mass spectrometry analyses were performed on polar and non-polar leaf extracts from Eucalyptus globulus, Eucalyptus grandis, Eucalyptus robusta, and Eucalyptus tereticornis (Myrtaceae). Feeding preferences were assessed in two-choice laboratory bioassays resulting in a preference gradient of the four plant species. Moreover, a performance bioassay where we contrasted survival and development time between the most and least preferred plants, showed a clear correlation with preference both in survival and developmental time of the most susceptible nymph instar. We found that species with high or low feeding preferences differ significantly in several foliar metabolites, which may be acting as feeding stimulants or deterrents for T. peregrinus. These findings may provide useful criteria for choosing Eucalyptus genotypes when planting in bronze bug infested areas.

Wide Distribution and Intraspecies Diversity in the Pathogenicity of Calonectria in Soil from Eucalyptus Plantations in Southern Guangxi of China.

Eucalyptus spp. are extensively cultivated in southern China because of their adaptability and versatile timber production. Calonectria leaf blight caused by Calonectria species is considered a major threat to Eucalyptus trees planted in China. The GuangXi Zhuang Autonomous Region is the provincial region with the largest distribution of Eucalyptus plantations in China. The present study aimed to expound the species diversity and pathogenicity of Calonectria isolates obtained from the soil of Eucalyptus plantations in GuangXi. A total of 188 Calonectria isolates were recovered from the soil located close to Eucalyptus trees, and the isolates were identified based on the DNA sequence comparisons of the four partial regions of the translation elongation factor 1-alpha (tef1), β-tubulin (tub2), calmodulin (cmdA), and histone H3 (his3) genes. The isolates were identified as Calonectria aconidialis (74.5%), C. hongkongensis (21.3%), C. pseudoreteaudii (2.1%), C. kyotensis (1.6%), and C. chinensis (0.5%). The inoculation results indicated that 40 isolates representing five Calonectria species were pathogenic to the three Eucalyptus genotypes. Two inoculated experiments consistently showed that the longest lesions were produced by the isolates of C. aconidialis. Some isolates of C. aconidialis, C. hongkongensis, and C. kyotensis produced significantly longer lesions than the positive controls, but not the isolates of C. pseudoreteaudii or C. chinensis. These results indicated that Calonectria isolated from the soil may pose a threat to Eucalyptus plantations. Some Calonectria isolates of the same species differed significantly in their virulence in the tested Eucalyptus genotypes. The resistance of different Eucalyptus genotypes to Calonectria isolates within the same species was inconsistent. The inoculation results in this study suggested that many Calonectria isolates in each species had different levels of pathogenicity, and many Eucalyptus genotypes need to be tested to select disease-resistant Eucalyptus genetic materials in the future. The results of the present study enhance our knowledge of species diversity and the potential damage caused by Calonectria in the soil of Eucalyptus plantations. Our results also provide new insights into the breeding of disease-resistant Eucalyptus genotypes for controlling Calonectria leaf blight in China in the future.

Morphological, physiological and carbon balance response of Eucalyptus genotypes under water stress

Morphological, physiological and carbon balance response of Eucalyptus genotypes under water stress

Calonectria species associated with diseased leaves and soils in southern China Eucalyptus plantations

Calonectria leaf blight (CLB) is one of the most important diseases of Eucalyptus trees grown in plantations. This disease poses a serious threat to the sustainability of Eucalyptus plantations in southern China. To better understand the causal agents of CLB, we collected samples of diseased leaves and soil from Eucalyptus plantations from nine regions in Guangdong Province where the disease has become a serious problem. A total of 606 Calonectria isolates were purified from the samples, with 399 and 207 originating from diseased leaves and soils, respectively. Phylogenetic analyses utilizing six gene regions resolved 303 isolates in the C. kyotensis species complex and an equal number of isolates in the C. reteaudii species complex. These two complexes were represented by ten known Calonectria species, including C. aconidialis (12.0%), C. curvispora (0.3%), C. hongkongensis (24.8%), C. ilicicola (0.9%), and C. kyotensis (12.0%) in the C. kyotensis species complex, and C. crousiana (1.0%), C. Guangdongensis (0.3%), C. pseudoreteaudii (40.7%), C. queenslandica (7.3%), and C. reteaudii (0.7%) in the C. reteaudii species complex. Pathogenicity tests showed that all species were capable of causing disease on two tested Eucalyptus genotypes, albeit at varying degrees of aggressiveness. Most isolates (98.3%) in the C. reteaudii species complex were from the diseased leaves, indicating that species in this complex are the main causal agents of CLB outbreak. In addition, a significant number of the C. kyotensis species complex isolates (66.7%) from the soil samples could also cause the disease on Eucalyptus leaves.

Eucalyptus scab and shoot malformation: a new disease in South Africa caused by a novel species, Elsinoe masingae

Abstract A serious new disease of Eucalyptus was detected in South African plantations of these trees during the summer of 2021/2022. The first symptoms are minute dark spots on young leaves, petioles and shoots, becoming scab-like as the spots age. On highly susceptible Eucalyptus genotypes, leaves and shoots can become malformed leading to a ‘feathering’ appearance in the tree canopies and in the case of heavy infections, leaf and shoot death occur. Isolations made directly from developing scabs resulted in slow-growing cultures. These were identified, based on phylogenetic analyses of DNA sequence data for the ITS, LSU, TEF1 and RPB2 regions, as a novel species of Elsinoe (Elsinoaceae, Myriangiales), described here as E. masingae. Inoculations of an Eucalyptus grandis × Eucalyptus nitens hybrid variety produced the same symptoms as those observed under natural conditions and the pathogen could be re-isolated from the emerging lesions. Elsinoe masingae is closely related to, but clearly distinct from, the recently described Elsinoe necatrix that causes a serious scab and shoot malformation disease on Eucalyptus in Indonesia. Field surveys revealed significant variation in the susceptibility of different Eucalyptus genotypes, with the most severely affected genotypes including an E. grandis × nitens and an E. grandis × urophylla hybrid variety and E. grandis. The disease has also been observed on Eucalyptus amplifolia and on Eucalyptus dunnii, which had mild infections. The observed variation in susceptibility of Eucalyptus planting stock should provide opportunities to avoid serious damage because of scab caused by E. masingae in the future.

Differences in rainfall interception among Eucalyptus genotypes

Differences in rainfall interception among Eucalyptus genotypes

Metabolic, Nutritional and Morphophysiological Behavior of Eucalypt Genotypes Differing in Dieback Resistance in Field When Submitted to PEG-Induced Water Deficit

Dieback is a physiological disorder that has caused losses on eucalyptus plantations. Thinking that water stress is one of the triggers for the physiological disorder and aiming at the early identification of tolerant genotypes, we evaluated plantlets of four commercial clones with divergent behavior in field conditions. The plantlets were grown in a greenhouse where the drought conditions were provided by the application of polyethylene glycol 6000 solutions at 100 and 300 g L−1. After water deficit treatments, the morphological, physiological, nutritional and metabolic analyses were performed. SuzT maintained the carbon fixation and the instantaneous water use efficiency, even under water deficit, while sustaining growth. This resulted in higher leaf area and total dry mass in SuzT. Despite higher photosynthetic rate, SuzS exhibited reduced dry biomass accumulation, implying less efficient carbon use. SuzT revealed a higher level of calcium that supports cell structure and homeostasis and indicates higher capacity to manage specific resources and survival under water deficit. SuzT suffered reduction in some free amino acids; however, there was no significant variation for total amino acid content. The principal component and cluster analyses indicated that SuzMT and SuzTP genotypes behave similarly to SuzT under water deficit, while SuzS clustered in isolation. Our results support that there are common trends in water deficit responses for contrasting eucalypt genotypes. The existence of other strategies coping with water deficit resistance is not discarded and should be further evaluated.