Diseases Of Eucalyptus Research Articles

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.

Ceratocystis wilt on Eucalyptus: first record from South Africa

Wilt and death of an E. grandis × E. urophylla variety was recently observed in the Zululand region of KwaZulu-Natal, South Africa. Symptoms on the dying trees included a streaking pattern of discolouration in the sapwood and cambium of stems and roots. A fungus resembling a Ceratocystis sp. was consistently found sporulating on diseased material and isolated from the symptomatic root and stem tissue. DNA sequence analyses of the Ceratocystis isolates, including multiple gene regions, identified the isolates as C. eucalypticola. Multiple ITS types were identified among the isolates sequenced, similar to those found in other, closely related, Ceratocystis species. Artificial inoculations under field conditions confirmed the pathogenicity of the isolates. This is the first report of a Ceratocystis sp. causing a wilt disease of Eucalyptus in South Africa.

Root infection and aerial colonization of eucalypt host plants by Erwinia psidii

Dieback, caused by Erwinia psidii is currently one of the most severe emerging diseases of Eucalyptus spp. in Brazil. Because of its recent report, little is known about the mechanisms underlying bacterial infection. We studied the colonization and movement of E. psidii in host tissue using a strain labeled with green fluorescent protein. We were able to transform E. psidii with pGreen-TIR and to demonstrate plasmid stability in the absence of antibiotic selection both in vitro and in vivo. We demonstrate that tissue colonization by E. psidii is not restricted to the inoculation point (leaf axil). E. psidii colonizes the xylem vessels, sclerenchyma and parenchyma of leaves and stems of eucalypt. At 35 days after inoculation, the bacterium was found at 5 cm above the inoculation point, indicating that it colonizes the plant acropetally. Confocal microscopy analysis revealed that when root-inoculated the bacterium penetrates the primary and secondary roots and reaches the xylem, but it was never found in the root crown or stem, irrespective of the evaluation time. Our results provide insights into the biology of the E. psidii-eucalypt interaction, which requires a better understanding in order to design efficient strategies for pathogen control and disease management.

Infection process of Puccinia psidii in Eucalyptus grandis leaves of different ages

Rust caused by Puccinia psidii is a serious disease of Eucalyptus and other Myrtaceae. Here we evaluated the pre-penetration processes in leaves at different phenological stages of a susceptible clone (3918) of Eucalyptus grandis. The first ten leaves, from the tip to the base, on the apical branch were detached and inoculated with urediniospores. We found a gradual reduction in fungal germination (88 to 39 %), apressorium formation (78 to 18 %), penetration (69 to 0 %) and sporulation (90 to 0 number of sorus /cm 2 )w ith the increase in leaf age. In addition, thickness and amount of wax was higher in the older leaves. The results of this study suggest that resistance to P. psidii infection in older Eucalyptus leaves occurs at the pre-penetration stage.

Detection of QTL associated with rust resistance using IBD-based methodologies in exogamic Eucalyptus spp. populations

In Brazil the rust caused by Puccinia psidii Winter stands out as the most important disease of eucalyptus. The use of resistant genotypes is the main control method, which makes the detection of markers linked to rust resistance essential to the selection of resistant genotypes. In this study, an F1 progeny of 131 plants from interspecific crossings of Eucalyptus was used to identify markers linked to resistance genes for this pathogen. An integrated map was constructed for linkage group three based on microsatellite markers. For QTL mapping two methodologies based on alleles identical-by-descent (IBD) were used: single marker analysis of Haseman and Elston and the interval mapping procedure of Fulker and Cardon. Both methods showed significant association for the Embra 125 marker.The QTL that explained 42 % of the phenotypic variation was mapped to 0.02 cM of this marker by the Fulker and Cardon. Marker Embra 125 has potential use in assisted selection, thus increasing the efficiency of the selection of resistant genotypes.

Puccinia psidii infecting cultivated Eucalyptus and native myrtaceae in Uruguay

Eucalyptus or guava rust caused by Puccinia psidii is a serious disease of Eucalyptus and other Myrtaceae. In Uruguay, it has been previously found on Eucalyptus globulus and Psidium brasiliensis. Almost nothing is known regarding the occurrence of this pathogen on other Eucalyptus species or native Myrtaceae in that country. In this study, we determined the presence of P. psidii on Eucalyptus species and native Myrtaceae trees in Uruguay and evaluated the pathogenicity of specimens from native myrtaceous hosts on E. globulus and E. grandis. Phylogenetic analyses based on the internal transcribed spacer (ITS) region of the nuclear ribosomal DNA operon were used to confirm pathogen identity. Comparisons of ITS sequences confirmed the identity of P. psidii on Eucalyptus globulus, E. grandis, Myrcianthes pungens, and Myrrhinium atropurpureum var. octandrum. This is the first report of P. psidii on M. atropurpureum var. octandrum. Pathogenicity tests showed that isolates from native Myrtaceae could infect both Eucalyptus species tested, indicating a strong biological relationship between both introduced and native Myrtaceae. This study supplies relevant field data, morphological information, molecular phylogenetic analyses and infection studies that contribute to a better understanding of an important and little studied pathogen.

First record of the Eucalyptus stem canker pathogen, Coniothyrium zuluense from Hawaii

A new stem canker disease on Eucalyptus grandis in Hawaii is recorded. Symptoms are similar to those of Coniothyrium canker on Eucalyptus in South Africa. A fungus resembling Coniothyrium zuluense was found on lesions and analysis of ITS sequences confirmed this identification. Coniothyrium canker is a serious disease of Eucalyptus in South Africa and strategies to reduce its impact in Hawaii may be required.

The use of RAPD-PCR analysis for the differentiation of Mycosphaerella species from Eucalyptus in Australia

Mycosphaerella contains some of the most damaging foliar pathogens of Eucalyptus. Identification of the species has relied mainly on characters such as ascospore morphology and the mode of ascospore germination. Wide variation and overlap in morphological characters, especially ascospore shape and size, has lead to confusion in species concepts. This study examines the potential of RAPD-PCR to differentiate Mycosphaerella species that cause leaf diseases of Eucalyptus in Australia. RAPD-PCR was conducted on 39 isolates representing 10 species of Mycosphaerella collected from southern Australia. Primers were chosen mainly to distinguish between the two most common and damaging species in Australia, M. cryptica and M. nubilosa. The RAPD analysis revealed five groups within the 39 isolates, four of which represent distinct species: M. cryptica, M. gregaria, M. nubilosa and M. marksii. For these four species, the cluster analysis and RAPD patterns gave results that fitted well with classical taxonomic criteria. Variation within M. cryptica, M. nubilosa and M. marksii was low, even though the isolates within these species originated from diverse hosts and locations. The remaining species in this study grouped together and could not be easily separated using the RAPD data here.

Mycosphaerella spp. and Their Anamorphs Associated with Leaf Spot Diseases of Eucalyptus

Mycosphaerella spp. and Their Anamorphs Associated with Leaf Spot Diseases of Eucalyptus

Phylogeny of Cryphonectria cubensis and allied species inferred from DNA analysis

Cryphonectria cubensis causes a serious canker disease of Eucalyptus in many tropical areas of the world. The aim of this study was to determine the phylogenetic relationships among strains of C. cubensis and the related species C. parasitica, Endothia eugeniae and E. gyrosa using DNA sequence data. A second objective was to develop a rapid diagnostic method to distinguish among these taxa. The variable ITS1 and ITS2 regions, as well as the conserved 5.8S gene of the rRNA operon, were amplified and sequenced. The amplified PCR products were also used in Alu I and Cfo I restriction digests. Analysis of the restriction profiles indicate that it is possible to distinguish between C. cubensis, C. parasitica, E. eugeniae and E. gyrosa using RFLPs (restriction fragment length polymorphisms). This will facilitate the identification of isolates thought to represent C. cubensis that sporulate poorly in culture. Analysis of the sequence data showed that C. cubensis isolates form a distinct clade that includes a strain from clove that might otherwise have been assigned the name E. eugeniae. Isolates of C. parasitica formed a separate clade. Endothia gyrosa grouped separately from both C. cubensis and C. parasitica.

Further Mycosphaerella species associated with leaf diseases of Eucalyptus

Three new species of Mycosphaerella are described from diseased leaves of Eucalyptus growing in a species trial in south-eastern Australia: Mycosphaerella marksii sp. nov. was associated with circular to irregular, sometimes confluent lesions, bordered by a prominent red-brown margin on several species of Eucalyptus; M. grandis sp. nov. and M. aggregata sp. nov. were associated with lesions confined to the leaf margin, extending from the tip almost back to the petiole, on leaves of E. grandis. It is likely that M. grandis is a primary parasite and M. aggregata a secondary invader. The species are distinguished mainly by their ascospore morphology and germination. Discrepancies between spore dimensions recorded in this and a previous study are explained by differences in the stains used.

Mycosphaerella nubilosa, a synonym of M. molleriana

Mycosphaerella leaf blotch is a serious disease of Eucalyptus in South Africa. Both M. nubilosa and M. molleriana have been reported to occur in this country. An examination of numerous collections has failed to show reliable differences between collections identified as either M. nubilosa or M. molleriana. Further studies have shown the type of M. molleriana to be incorrectly measured, and that the two species are conspecific, with M. nubilosa being a synonym of the earlier described M. molleriana.

In vitro evaluation of fungicides against Cylindrocladium spp. causing diseases of Eucalyptus in Kerala, India

A total of 22 fungicides were evaluated in vitro for their efficacy against Cylindrocladium quinqueseptatum (CQ), C. ilicicola (CI), C. floridanum (CF), C. parvum (CP), and C. camelliae (CC) causing various diseases of Eucalyptus in Kerala, India. Though there were a number of fungicides effective (ED100) in the comdial germination and poisoned food techniques, only carbendazim provided complete inhibition of CQ, CI and CC in the soil-fungicide screening technique; carbendazim was also highly effective against CF and CP. C. ilicicola appeared to be more tolerant than other species of Cylindrocladium as only a few fungicides were found to be effective against it even in the conidial germination technique. On comparison of the three fungicidal evaluation techniques, it is concluded that, for a pathogen producing microsclerotia, like Cylindrocladium, the soil-fungicide screening technique is the most appropriate one for obtaining reliable results.

CryphonectriaCanker ofEucalyptus, an Important Disease in Plantation Forestry in South Africa.

SYNOPSIS Cryphonectria cubensis, one of a notorious group of canker pathogens of trees and the cause of a serious disease of Eucalyptus, has recently been found in South Africa for the first time. This review provides the first compilation of the literature pertaining to Cryphonectria canker and attempts to critically summarise current knowledge of the disease. Specific attention is given to the South African forestry situation and the likely impact that the disease might have in this country. Proposals for future research are also considered.

Spore production by Mycosphaerella species causing leaf diseases of Eucalyptus

The production of ascospores of Mycosphaerella nubilosa and M. cryptica was monitored at two field sites at monthly intervals. Ascocarp initiation and early development occurred throughout the year. Ascospore production was greatest from summer to mid autumn; lower temperatures then appeared to limit ascospore production from late autumn to early spring. Adequate leaf wetness is also necessary for ascocarp development and spore production. Under laboratory conditions, ascospores of both fungi matured at 15 °C with 12 h but not 1 h leaf wetness daily. Ascocarps of M. nubilosa continued to discharge spores for up to 17 months in the field, while ascocarps of M. cryptica remained active for at least 8 months. Ascospore production by M. parva was often recorded on older lesions caused by M. nubilosa or M. cryptica supporting the hypothesis that this species is saprobic.

Further Mycosphaerella species causing leaf diseases of Eucalyptus

Three previously described species of Mycosphaerella are discussed in relation to their original descriptions and type specimens. M. eucalypti does not appear to be a species of Mycosphaerella . However M. heimii is a distinct species but no Latin diagnosis was provided by the original author and the type specimen could not be located. M. molleriana is also distinct but it has not yet been collected from eucalypts in Australia. Three new species are described from diseased eucalypt leaves collected in southern Australia: M. delegatensis sp.nov., M. swartii sp.nov., and M. walkeri sp.nov. M. swartii and M. walkeri have identical teleomorphs, but distinct anamorphs, Hendersonia eucalyptorum and H. fraseri respectively, and have different host ranges.

Leaf diseases of Eucalyptus associated with Mycosphaerella species

Two distinct types of leaf spot on juvenile leaves of Eucalyptus globulus were found to be caused by two species of Mycosphaerella. M. cryptica caused a small circular spot while M. nubilosa caused a larger, spreading lesion. M. parva Park & Keane was only found on older lesions caused by M. nubilosa, and appears to be saprophytic. M. cryptica was also shown to be the cause of large, blighting lesions on mature foliage of a wide range of species from both major subgenera of Eucalyptus. Observations on symptom development, sporulation, pathogenicity and leaf penetration for M. cryptica and M. nubilosa are presented. Preliminary results of field studies are also given.

Three Mycosphaerella species from leaf diseases of Eucalyptus

Three species of Mycosphaerella were found to be associated with two distinct types of lesion on juvenile leaves of Eucalyptus globulus. M. cryptica caused smaller circular lesions, but on mature leaves of many other eucalypt species it caused large blighting lesions. M. nubilosa has been found only on large, blighting lesions on juvenile leaves of E. globulus and three other species in the eucalypt subgenus Symphyomyrtus. A saprophytic species, which is described here as Mycosphaerella parva sp.nov., was commonly found on lesions in association with M. nubilosa.

Factors Influencing Suppression of Root Rot of Eucalyptus sieberi and E. obliqua Caused by Phytophthora cinnamomi

A krasnozem from the foothills of Mt Dandenong, Victoria, was found to strongly suppress root disease of Eucalyptus sieberi and E. obliqua seedlings caused by Phytophthora cinnamomi. Soil factors associated with disease suppression were examined in a phytotron by altering soil structure, using a hammer mill, sieves of various sizes and changing the soil microflora with steam at 60 and 100°C. E. sieberi, E. obliqua and E. globoidea were used as test seedlings. The results showed that the suppressive activity depended on the soil microflora and their association with the aggregates in the krasnozem. P. cinnamomi was found to kill seedlings by girdling the base of the stem and/or major roots. Some evidence showed that in unsteamed krasnozem aggregates many small roots were infected but few large roots and no stems were girdled, suggesting that post-infection antagonism occurred within the root. Field isolations from dead and dying E. sieberi, E. obliqua and E. regnans showed that P. cinnamomi infected the stems and major roots.