Ralstonia solanacearum decreases volumetric growth of trees and yield of kraft cellulose of Eucalyptus spp.

Ralstonia solanacearum is currently one of the most important plant pathogenic bacteria worldwide, with a wide geographical distribution and host diversity. The pathogen infects more than 200 plant species belonging to approximately 50 plant families, including Eucalyptus spp. Although, high losses have been reported in nurseries, little is known on the negative impact of the disease in the field. In this study, we evaluated the incidence of R. solanacearum and its effect on volumetric growth and cellulose yield of discoloured wood chips obtained from infected trees of one clone of Eucalyptus urophylla and two hybrid clones of Eucalyptus urophylla × E. grandis. The average incidence of bacterial wilt ranged between 60.6% and 72.4%. Volumetric growth of infected trees disease decreased 78.6% and 81.7% at 18 and 30 months, respectively. The pulp screen yield of three clones decreased between 3.2 and 6.4%, with an average 4.3%. The results of this work provide useful information on the losses of volumetric growth and pulp yield of eucalypt caused by R. solanacearum.     

Susceptibility of Eucalyptus grandis to Cryphonectria cubensis

Artificial inoculation of rooted Eucalyptus grandis cuttings with Cryphonectria cubensis in the glasshouse showed that significant differences exist in the susceptibility of various Eucalyptus clones to the pathogen. A 61.3% difference in susceptibility was observed between the most resistant and susceptible group of clones. Results appeared, however, to have been influenced by genotype × environment interaction.     

Wilt and die‐back of Eucalyptus spp. caused by Erwinia psidii in Brazil

A new disease of unknown bacterial aetiology has been observed in eucalyptus stands since 2009. It is characterized by die‐back, wilting and lesions on the branches, petiole and midrib in association with macroscopic and microscopic bacterial ooze. To date, this disease has been observed in stands of clonal Eucalyptus saligna, E. grandis and E. urophylla x E. grandis hybrids and in E. dunnii seedling plantations in the states of São Paulo, Rio Grande do Sul and Mato Grosso do Sul. Considering the economic importance of eucalyptus plantations and the potential losses caused by this disease, this study aimed to identify and characterize the causal agent. Thirty‐four strains were obtained from infected plants, which were collected in the field from four locations. The inoculation of detached leaves and intact rooted cuttings supported pathogenicity in eucalyptus. The phylogenetic analysis of four housekeeping genes (16S rDNA, gapA, recA and rpoB) as well as biochemical tests confirmed the identity of strains belonging to the species Erwinia psidii. This is the first report of E. psidii as the cause of wilt and die‐back in Eucalyptus spp. in Brazil.     

Stomatal characteristics of Eucalyptus grandis clonal hybrids in response to water stress

This study describes the stomatal response occurring during water stress and subsequent recovery of three Eucalyptus grandis clonal hybrids. The aim was to investigate the degree to which stomatal conductance (g _s) and stomatal density differ between the clonal hybrids across seasons and in response to water stress. Plants from one E. grandis × E. camaldulensis (GC) and two E. grandis × E. urophylla (GU1 and GU2) clones were grown for 18 months in 80 l planting bags. Plants were subjected to three watering treatments: control (100% field capacity), chronic water stress (maintained at 15% of field capacity) and acute water stress (cyclic water stress, where water was withheld until leaf wilting point, and a subsequent period of recovery followed). Stomatal conductance was measured after 6, 12 and 18 months growth. At 12 months of age, the recovery of g _s 1, 2 and 7 d after rewatering (following acute water stress) was further investigated. The GC hybrid showed consistently higher g _s than the GU clones at each measurement period. Stomatal conductance was 24–66% higher during winter (after 12 months growth) than during summer. The recovery of stomatal conductance from acute water stress was more rapid in the GC clone than the GU clones. Chronic water stress was shown to decrease g _s in GU clones by up to 70%, but not in the GC clone. Water stress did not affect stomatal density or size. Remarkably, stomata were absent from the adaxial leaf surface of clone GU1 leaves, but not from the leaves of the other E. urophylla hybrid cross (GU2). Total biomass of the GC clone was significantly greater at 9 months growth, but after 18 months growth the GU1 clone had attained greater biomass accumulation (although not significantly). Measurement of g _s, transpiration, stomatal density and total biomass in the GU1 clone indicated stomatal sensitivity to water stress, a favourable trait during periods of drought. The differing growth strategies of the GU and GC clones could be partially explained by their differences in stomatal sensitivity in response to water stress.     

Effect of environment on the response of Eucalyptus clones to inoculation with Cryphonectria cubensis

The ascomycete Cryphonectria cubensis causes severe losses in Eucalyptus plantations in South Africa and selection programmes for disease tolerance are necessary. The aim of this study was to use two C. cubensis inoculation trials, planted at different locations to assess the disease susceptibility of the clones and the effect of the environment on disease development. These two trials consisted each of 21 Eucalyptus clones (E. grandis, E. grandis × camaldulensis and E. grandis × urophylla). All trees were inoculated with a single virulent strain of C. cubensis and lesion widths measured 6 and 12 months after inoculation. Clones differed significantly in their tolerance to C. cubensis. Further, disease severity differed depending on the geographical location of the trial. A significant clone × locality (genotype × environment) interaction was observed. Therefore, screening for disease resistance should take place only in areas where clones will be commercially grown.     

Methods of inoculation and evaluation of Erwinia psidii in eucalypt

The dieback and wilting caused by Erwinia psidii are emerging eucalypt diseases that have been observed since 2014 in the south and central‐south regions of Brazil. Field observations have shown variability in disease severity resistance among Eucalyptus spp. clones and species. It is hypothesized that this variability is due to genetic resistance. To confirm this hypothesis, inoculations in genetically distinct eucalypt plants are necessary. However, lack of an inoculation method and disease assessment makes difficult to select resistant genotypes for use in commercial plantations or genetic breeding programmes. Three inoculation methods were tested on eight clones of Eucalyptus spp. Among them, inoculum deposition with bacteria‐impregnated toothpick on the axillary buds was the simplest and most effective, capable to reproduce the disease symptoms observed under conditions of natural infection. We also developed a rating scale for disease assessment. Among eight clones tested, only Clone 1 (Eucalyptus saligna) and Clone 2 (Eucalyptus urophylla) were resistant.     

Infestation Density of Eucalyptus Gall Wasp,Leptocybe invasa Fisher and La Salle (Hymenoptera: Eulophidae) on Five Commercially Grown Eucalyptus Species in Tanzania

This study explores infestation density of Leptocybe invasa on five commercially grown Eucalyptus species in Coastal, Plateaux, and Southern Highlands agroecological zones of Tanzania. Infestation density between agroecological zones, Eucalyptus species, age classes and tree crown parts, relationship between stand altitudes and the magnitude of infestation, damage index, species age, and abundance of L. invasa on different Eucalyptus species were examined. There were significant differences in infestation between zones and Eucalyptus species. Eucalyptus tereticornis was more affected, followed by E. camaldulensis, and E. saligna was the least while E. grandis and E. citriodora were not affected. No significant differences in damage between different crown parts were observed. Trees with age of 1–3 yr were damaged more than those of age 4–6 yr. Pest infestation increased with an increase of L. invasa abundance but decreased with an increase of altitudes. Control efforts needs to focus on controlling the spread of the pest, using silvicultural methods and planting resistant Eucalyptus species.     

Detection and characterization of Ralstonia pseudosolanacearum infecting Eucalyptus sp. in Brazil

Ralstonia solanacearum sensu lato causes bacterial wilt in many agronomic crops and tree species economically important worldwide. It is a species complex that has been divided into phylotypes and sequevars, commonly related to geographic distribution. Knowledge of the phylotype composition and genetic variability in populations of this phytopathogenic bacterium is useful for implementing effective control measures. In a survey conducted in 2019, six bacterial strains were obtained from wilted Eucalyptus urophylla trees in plantations located in the municipality of Dom Eliseu, Pará state, Brazil. Multiplex PCR based on the internal transcribed spacer (ITS) indicated that the bacterial strains belonged to two different species, namely R. pseudosolanacearum (phylotype I) and R. solanacearum (phylotype II). In a phylogenetic analysis, the nucleotide sequence of the endoglucanase (egl) gene from eucalypt strains of phylotype I clustered together with sequevar 18 sequences from GenBank. Separation of the strains into two different species was confirmed by repetitive element palindromic PCR (rep‐PCR). Pathogenicity tests demonstrated that the R. solanacearum and R. pseudosolanacearum strains recovered from E. urophylla cause disease in both tomato and eucalypt plants. Until now, only R. solanacearum (Phylotype II) has been reported causing wilt symptoms on Eucalyptus spp. in Brazil. Therefore, the presence of R. pseudosolanacearum and a need for better understanding of its genetic and aggressiveness variability as well as possible differences between the two species should be considered in breeding programmes aimed at the deployment of host resistance.     

Aboveground nutrient components of Eucalyptus camaldulensis and E. grandis in semiarid Brazil under the nature and the mycorrhizal inoculation conditions

A study was conducted to evaluate the aboveground biomass, nutrient content and the percentages of mycorrhizal colonization in Eucalyptus camaldulensis and Eucalyptus grandis plantations in the semiarid region (15° 09′ S 43° 49′ W) in the north of the State of Minas Gerais in Brazil. Results show that the total above-ground biomass (dry matter) was 33.6 Mg·ha⁻¹ for E. camaldulensis and 53.1 Mg·ha⁻¹ for E. grandis. The biomass of the stem wood, leaves, branches, and stem bark for E. camaldulensis accounted for 64.4%, 19.6%, 15.4%, and 0.6% of the total biomass, respectively (Table 2); meanwhile a similar partition of the total above-ground biomass was also found for E. grandis. The dry matter of leaves and branches of E. camaldulensis accounted for 35% of total biomass, and the contents of N, P, K, Ca, Mg, and S in leaves and branches accounted for 15.5%, 0.7%, 12.3%, 22.6%, 1.9%, and 1.4% of those in total above-ground biomass, respectively. In the trunk (bark and wood), nutrient accumulation in general was lower. Nutrient content of E. grandis presented little variation compared with that of E. camaldulensis. Wood localized in superior parts of trunk presented a higher concentration of P and bark contained significant amounts of nutrients, especially in E. grandis. This indicated that leaving vegetal waste is of importance on the site in reducing the loss of tree productivity in this semi-arid region. The two species showed mycotrophy.     

First report of Teratosphaeria gauchensis causing stem canker of Eucalyptus in Kenya

Teratosphaeria stem canker is an important disease of Eucalyptus species in many parts of the world where these trees are intensively propagated in plantations. Symptoms similar to those of Teratosphaeria stem canker were observed on Eucalyptus grandis and a E. grandis × E. camaldulensis hybrid clone in the Central Highlands of Kenya. Symptomatic bark samples were collected from two sites and the associated fungus isolated and identified using DNA sequence analyses of multiple gene regions. The pathogen was identified as Teratosphaeria gauchensis. This represents the first report of the disease and the pathogen in Kenya.     

Botryosphaeriaceae associated with Eucalyptus canker diseases in Colombia

The identities of Botryosphaeriaceae causing cankers on Eucalyptus in Colombia were investigated using morphological and DNA sequence comparisons. The pathogenicity of the species was also assessed on 42 Eucalyptus grandis clones planted at four different sites. Two species of the Botryosphaeriaceae were found to occur on E. grandis in Colombia. Neofusicoccum ribis was the more common species, and also the most pathogenic. Botryosphaeria dothidea was found only in one zone of Colombia, and was also less pathogenic than N. ribis. These two species could be distinguished easily based on DNA sequences of the ITS1/ITS2 rDNA region and EF1‐α, in addition to conidial sizes. Significant differences in resistance of clones to these pathogens were also evident from the various trials.     

Susceptibility of Eucalyptus hybrid clones to Botryosphaeria canker in Uganda

ABSTRACT

The study assessed the susceptibility of the nine commonly grown Eucalyptus clones to Neofusicoccum species associated with Botryosphaeria canker in Uganda. The inoculation trials indicated that susceptibility of Eucalyptus hybrids differed significantly (p = .000), clones GU609, GU7, GC578, and GC796 exhibiting a higher tolerance than GC784, GC550, GU8, GC514, and GC540. The results further revealed that N. parvum was more pathogenic than N. kwambonambiense. The generated information can be exploited in sustainable forest management by expanding the growing of tolerant hybrids in areas with high Botryosphaeria canker disease pressure.     

Spatiotemporal dynamics of bacterial wilt in Eucalyptus

Bacterial wilt (caused by Ralstonia spp.) is one of the most damaging diseases of Eucalyptus species, and is responsible for substantial losses to producers. For efficient, scientifically-based management of this disease, it is necessary to understand the various factors involved in its development, including greater knowledge of the epidemiology of the pathogen on Eucalyptus spp. This study aimed to determine the spatialtemporal dynamics of bacterial wilt in Eucalyptus under natural infection conditions. An experiment was conducted in a commercial plantation in the municipality of Itinga, state of Maranhão, Brazil, using the clone FGCA0385 (Eucalyptus urophylla var. platyphylla). The study comprised of four plots composed of 450 plants each, subdivided into nine rows with 50 plants per row with a spacing of 3 × 3 m. Disease incidence was quantified over 1 year. The spatial dynamics of the disease was determined using the dispersion index, a modified Taylor law, and the analysis of the dynamics and structure of foci. For temporal dynamics, the curve of the disease incidence progress was plotted, and the data were analysed by simple linear regression analysis fitted to three empirical models: logistic, monomolecular, and Gompertz. The distribution pattern of Eucalyptus bacterial wilt was random, as confirmed by the Index of dispersion. Analysis of the dynamics and structure of the foci, showed that 69 disease foci occurred, 44 of which were unitary, with an average number of plants per focus of 1.63. Foci had greater length in the direction of the planting line. The epidemics were best described by the monomolecular model, with an estimated incidence of Eucalyptus bacterial wilt of 27.77% in the fourth year of the study. According to the spatiotemporal dynamics of this work, management strategies such as eliminating symptomatic plants and crop renovation can be used based on economic viability.     

Comparison of taper functions between two planted and coppiced eucalypt clonal hybrids, South Africa

In addition to regeneration through seed, certain eucalypts are able to regenerate via the production of coppice shoots following felling, which can then be selectively thinned over time and managed as a coppice stand for the commercial production of timber. Little information could be found if tree form differs between coppiced (where one or two stems had been left per stump) and planted eucalypts, or whether different volume taper models would need to be developed. To determine if this was necessary, rotation-end stem taper data was collected from an Eucalyptus grandis × E. urophylla and an E. grandis × E. camaldulensis trial to compare volume taper equations for planted versus coppiced commercially grown Eucalyptus clonal hybrids. For treatment comparisons, taper data were collected from the parent crop (1R), the replanted crop (2R), as well as from coppiced stands where either a single (Cop_Sngl) or double stem (Cop_Dbl) had been left per stump. Stem taper functions used for treatment comparisons indicated differences between clones, as well as between treatment, with the models based on single stems (1R, 2R or Cop_Sngl) being significantly different from those containing two stems (Cop_Dbl). Despite any non-significant model differences (for example between 1R, 2R and Cop_Sngl single stem crops) the percentage magnitude of any bias in utilizable volume differences when comparing the individual models (between a 6.31% over-prediction to a 3.8% under-prediction) still needs to be taken into account as these differences may have importance in terms of the volume and product prediction.     

Clonal variation in growth, arsenic and heavy metal uptakes of hybrid Eucalyptus clones in a Mediterranean environment

Variation in growth, arsenic and heavy metal uptakes by aboveground tissues (leaves, stems and branches) of 13 hybrid Eucalyptus clones selected for biomass production in a Mediterranean environment (E. camaldulensis × E. viminalis; E. camaldulesis × E. grandis; E. camaldulensis × E. globulus subsp. bicostata) was investigated on agricultural soils field-contaminated with arsenic (As), cadmium (Cd), chrome (Cr), lead (Pb), copper (Cu) and zinc (Zn) in an ex situ nursery experiment in central Italy. Large variation in growth and contaminant uptake amongst the tested clones was observed. All plants survived and 12 clones grew better than the control (E. camaldulensis). All clones accumulated the contaminants to which they were exposed: As, Cu, Pb and Zn concentrations were significantly higher in leaves than in stems and branches, supporting the potential for phytoremediation of these contaminants by Eucalyptus short rotation woody crops (SRWC). Significant positive correlations between the average contents of Cd–Pb, Cd–Cu, Cd–Zn, Pb–Cu, Pb–Zn and Cu–Zn in the aboveground tissues were detected. Clones revealed better phytoextraction performance than that of the control. Four promising clones for biomass production and phytoremediation were identified for prospective use in SRWC on contaminated soils in Mediterranean environments.     

Lesion size induced by Chrysoporthe fungal pathogens varies between Eucalyptus species and geographic locations in Zambia

Chrysoporthe canker disease is one of the serious threats facing planted Eucalyptus in southern Africa. In order to manage this disease, planting of less susceptible species of Eucalyptus has been promoted in many countries but it is not clear which species are less susceptible for Zambian environments. The purpose of this study was to test the response of different Eucalyptus species to Chrysoporthe fungal pathogens under field conditions to identify the least susceptible species to the disease. Two-year-old Eucalyptus trees (E. grandis, E. camaldulensis, E. cloeziana and E. tereticornis) growing in low- and high-rainfall locations were inoculated separately with three Chrysoporthe fungal species (C. austroafricana, C. syzygiicola and C. zambiensis) and the induced lesion size was measured six months after inoculation. Analysis of variance revealed that lesion size differed significantly between Eucalyptus species (F_3,948 = 1 978.8, p < 0.001). Lesion size on Eucalyptus species increased in the order E. camaldulensis < E. teriticornis < E. cloeziana < E. grandis. On average, trees growing in the higher-rainfall site produced significantly larger lesions than trees growing in the low-rainfall site (F_1,948 = 565, p < 0.001), suggesting that location influences disease severity. Smaller lesions on E. camaldulensis indicate lower susceptibility to Chrysoporthe canker disease, providing an opportunity to use this species in the selection and breeding for resistant Eucalyptus genotypes for plantation development in high disease-risk sites in Zambia.     

First report of Puccinia psidii on Corymbia citriodora and Eucalyptus in Colombia

A rust disease was observed during routine disease surveys of Eucalypt species in Colombia. The cause of the disease was identified, using morphology and DNA sequence data, as the myrtle rust pathogen, Puccinia psidii. We evaluated the susceptibility of Eucalyptus grandis and the hybrid Eucalyptus urograndis to P. psidii. This is the first report of this pathogen on Corymbia citriodora and Eucalyptus species in Colombia.     

Variation in growth potential between hybrid clones of <Emphasis Type="Italic">Eucalyptus</Emphasis> trees in eastern South Africa

Growth of commercial forestry is highly dependent on the availability of fast-growing planting materials. Consequently, the efficient utilization of fast-growing plantations can greatly impact productivity. The objectives of this study were to evaluate variations in the growth potential of two clones and to estimate the average stem radial growth advantage of a fast-growing clone using data obtained from Sappi landholdings in eastern South Africa and a mixed modelling approach that permits the incorporation of covariance structure into the statistical model. During the first 2 years of growth, the stem radius of nine trees each of two clones was measured using dendrometer attached to the tree. A second-degree fractional polynomial model was chosen to show the functional relationship between stem radius and tree age. Growth of the two hybrid clones differed significantly. The Eucalyptus grandis × Eucalyptus urophylla clone grew faster than the E. grandis × camaldulensis clone, indicating better genetic potential for rapid growth and yield. This study can be considered as starting point to further compare the potential for rapid growth of several hybrid clones using the longitudinal data modelling approach.     

Pestalotiopsis biciliata,a new leaf pathogen of Eucalyptus spp. recorded in Italy

The present paper describes new symptoms on Eucalyptus spp. in Central Italy associated with the fungal pathogen Pestalotiopsis biciliata. This fungal species has been previously recorded in Italy on grape associated with fruit rot. Artificial inoculation trials on leaves confirmed the pathogenicity of the fungus to Eucalyptus camaldulensis. P. biciliata is included in the list of Pestalotiopsis spp. responsible for leaf disease on eucalypts worldwide.