First report of Sphaeropsis canker on cypress in South Africa

In this study a Sphaeropsis sp. is recorded as causing cankers on cypress in South Africa. These cankers are either found alone or on trees which are infected with the well-known cypress canker pathogen, Seiridium unicorne. When the two fungi occurred together, lesions could not be distinguished from each other, although the greater number of lesions were caused by the Sphaeropsis sp. The fungus appears to be identical to that described as Sphaeropsis sapinea f.sp. cupressi, in Israel, which is a fungus very different from the pine pathogen, Sphaeropsis sapinea. Pathogenicity tests showed that the Sphaeropsis sp. is significantly more pathogenic to Cupressus lusitanica than to Pinus roxburgii and Pinus elliottii. S. sapinea was pathogenic only to the Pinus spp. tested, and not to C. lusitanica. In contrast, the cypress pathogen Seiridium unicorne, was pathogenic to C. lusitanica and also to the two Pinus spp. tested.     

Differential reaction in Pinus spp. to inoculation by various isolates of Ascocalyx (Gremmeniella) abietina

Stem inoculations of 3 species of pole-size pines with 4 diverse isolates of Ascocalyx (Gremmeniella) abietina revealed Pinus pinea to be more susceptible than either P. pinaster or P. nigra in terms of canker length. Isolate type and geographical aspects considered more briefly, also have some effect.     

Resistance levels of Spanish conifers against Fusarium circinatum and Diplodia pinea

Pitch canker, caused by Fusarium circinatum, and Diplodia shoot blight, caused by Diplodia pinea, are both damaging to pines (Pinus spp.) grown in plantations throughout the world, including Spain. To assess the potential for interspecific differences in susceptibility to contribute to the management of pitch canker and Diplodia shoot blight in the Atlantic region of Spain, the present study was undertaken to characterize the susceptibility of six pine species (P. sylvestris, P. nigra, P. pinaster, P. radiata, P. halepensis and P. pinea) and Douglas‐fir (Pseudotsuga menziesii) to F. circinatum and D. pinea. Based on inoculations of 2‐year‐old trees, Ps. menziesii, P. pinea and P. nigra were the most resistant to F. circinatum, with lesion lengths ranging from 3.7 to 21.5 mm, 2.2 to 12.6 mm and 2.8 to 30.9 mm, respectively. At the other extreme, Pinus radiata was the most susceptible, sustaining lesions that ranged from 8.5 to 74.8 mm in length. Pinus sylvestris, P. pinaster and P. halepensis showed an intermediate response to F. circinatum. Broadly similar results were observed in inoculations with D. pinea, with Ps. menziesii being relatively resistant and P. radiata being highly susceptible. Consistent with these results, field surveys revealed no pitch canker in stands of Ps. menziesii and low severity of Diplodia shoot blight, whereas P. radiata was severely affected by both diseases. Our findings suggest that selection of appropriate species can greatly reduce the risk of damage from two important canker diseases affecting pine plantations in the Atlantic region of Spain. Furthermore, intraspecific variation in susceptibility implies that selection may allow for the enhancement of resistance in otherwise susceptible species.     

Canker of cypresses caused by Coryneum cardinale Wag. in Britain

Coryneum canker occurs widely on Cupressus macrocarpa in England. Mycelial inoculations caused perennial cankers on Cupressocyparis leylandii and Chamaecyparis nootkatensis, severe but annual cankers on Thuja plicata and death of twigs on Juniperus communis. Chamaecy-paris lawsoniana rapidly overcame initial infection. Conidial inoculations on C. leylandii caused cankers. The potential of the disease in Britain and its control are discussed and aids to the identification of the fungus in culture given.     

Histopathologie du chancre cortical du cypres à Seiridium cardinale

Histopathology of cankers on Cupressus caused by Seiridium cardinale . The purpose of this work was to understand host defense reactions of cypress trees against S. cardinale canker to improve selection of clones resistant to the disease. Following infection, bark recovery depends on the neophellogenic efficiency to build a necrophylactic periderm (NP) that compartmentalizes the diseased tissue. The thicker the NP the more resistant the bark. Neophellogenic activity can be estimated by measuring the thickness of constitutive phelloderm of the bark of trees from natural plantings or seedlings. Potentially resistant clones having phelloderms thicker than 100μm will be selected for further experiments.     

‘Le Crete 1’ and ‘Le Crete 2’: two newly patented Seiridium cardinale canker‐resistant cultivars of Cupressus sempervirens

In the Mediterranean area, common cypress (Cupressus sempervirens) has traditionally been used as a multipurpose tree, for its symbolic and ornamental role, for its valuable timber, as well as for windbreaks and soil protection. The epidemic spread of the Seiridium cardinale canker has limited the use of this tree since the 1970s, inducing researchers to develop a breeding programme of cypress aimed at selecting canker‐resistant lines for different uses and to support a flourishing trade of cypress plants. ‘Le Crete 1’ and ‘Le Crete 2’ described here are two new canker‐resistant C. sempervirens varieties patented in 2010, selected through a 13‐year assessment of their response to artificial inoculations and growth traits. Both are characterized by a rapid growth and by a columnar and fastigiated habit that confers them a notable ornamental effect. Preliminary observations showed also that both tend to produce yearly few microsporophylls and little pollen. ‘Le Crete 2’ was also selected for the high growth rate it maintained on heavy, clayey soils.     

Fusarium canker of Italian cypress

A new disease, causing mortality of Italian cypress (Cupressus sempervirens) trees cv. ‘Totem', was observed in an Israeli nursery. Fusarium compactum was isolated from cankers, and its pathogenicity was confirmed by Koch's test. The fungus readily formed conidia and chlamydospores in PDA culture. Growth of F. compactum was fastest at 26–30°C. Artificial inoculations with F. compactum caused severe cankering of several species of each of the following coniferous genera: Cupressus, Juniperus, Tetraclinis, Thuja, Cedrus and Pinus. Canker development was significantly enhanced when extreme water stress was imposed on cypress saplings prior to inoculation.     

Pathogenic variability of various isolates of Seiridium cardinale,S. cupressi and S. unicorne inoculated on selected Cupressus clones and seedlings

Comparative studies of the pathogenicity of eight isolates of three Seiridium species were carried out by stem inoculations on Cupressus sempervirens and C. glabra seedlings and clones. Seiridium cardinale and S. cupressi caused bigger and more severe cankers than all strains of S. unicorne. During the first nine months after inoculation, the canker length of S. cardinale was larger than the cankers of S. cupressi. However, during the second year after inoculation, S. cupressi cankers were larger and more severe than those of 5. cardinale.     

Informative value of canker morphology on the presence or absence of virus infection in chestnut blight cankers

Chestnut blight destroyed the native chestnut forests in North America and also severely affected the European chestnut trees after its introduction in the 20th century. The ascomycete fungus Cryphonectria parasitica is responsible for this serious disease and causes lethal bark cankers on susceptible chestnut trees. In Europe, however, an infection of C. parasitica with Cryphonectria hypovirus 1 (CHV‐1) causes hypovirulence in C. parasitica and reduces the severity of the disease. Hypovirulence biologically controls chestnut blight in many regions to date. In this study, our goal was to determine morphological canker characteristics that are indicative of virus presence or absence in C. parasitica. We investigated 677 chestnut blight cankers from seven different geographic locations across Europe. For each canker, we assessed canker length, stem encircling, canker depth, presence of sporulation, canker activity and virus infection. We statistically analysed the informative value of these morphological characteristics for the presence or absence of CHV‐1. However, we did not find reliable indicators. Our logistic regression analysis revealed that virus infection of C. parasitica is not clearly related to canker morphology. This implies that fungal isolations from chestnut blight cankers and assessments in the laboratory are required to determine infection with CHV‐1 unequivocally.     

Leptoglossus occidentalis and Diplodia pinea: a new insect‐fungus association in Mediterranean forests

Leptoglossus occidentalis, an insect native to North America, was inadvertently introduced into Italy about 1999. The insect damages the cones of conifer trees, especially Pinus pinea (Italian Stone pine). Pinus pinea is also affected by Diplodia pinea, a fungus native to Italy, which is becoming an increasing threat because pine trees are becoming more susceptible to it as a consequence of global warming. Because the insect and the fungus both have the pine cones as a common habitat, a possible interaction between them has been postulated. The aim of this study was to ascertain whether L. occidentalis and D. pinea interact on P. pinea cones. The interaction was studied using real‐time PCR on a group of naturally infected insects collected from a forest, and a group raised in the laboratory and artificially inoculated with D. pinea conidia. Molecular analysis showed that D. pinea DNA occurred on both naturally infected and inoculated insects, but with significant differences between the two groups. The rapid and sensitive molecular technique made it possible to detect D. pinea DNA on the bodies of the insects, and to show that the native D. pinea occurred on the exotic insect.     

Testing of selected South African <Emphasis Type="Italic">Pinus</Emphasis> hybrids and families for tolerance to the pitch canker pathogen, <Emphasis Type="Italic">Fusarium circinatum</Emphasis>

Plantations of Pinus spp. constitute approximately 50% of the South African forestry industry. The first aim of this study was to develop a reliable inoculation technique to screen Pinus spp., for tolerance to infection by F. circinatum, which threatens pine forestry in South Africa. Inoculation of branches was compared with stem inoculations and we considered the number of branches or trees required to obtain statistically significant results. Furthermore, variation in the susceptibility of some Pinus families, clones and hybrids was considered. Results showed that branch inoculations were closely correlated with those from stem inoculations, and that it is important to consider branch and stem diameters when assessing susceptibility of trees. Subsequent trials using branch inoculations showed significant differences in F. circinatum tolerance amongst a range of pine species and hybrids of potential interest to forestry in South Africa. Significant differences in susceptibility were also found among clones of two P. radiata families. The most tolerant trees were P. elliottii × caribaea and P. patula × oocarpa hybrids, while the most susceptible species were P. patula, P. greggii and hybrids of these two. This is the first trial considering the susceptibility of Pinus hybrids, Pinus clones and some P. patula provenances, and the results indicate excellent potential for breeding for tolerance to pitch canker in South Africa. Application The accurate selection of disease tolerant planting stock for the South African forestry industry is crucially important for the continued sustainability of this important industry. The work described here provides valuable information on an artificial inoculation technique that will assist the industry in screening trees for tolerance to the pitch canker fungus, F. circinatum. It also provides some indication of the relative susceptibility of a number of Pinus spp., hybrids and families currently being evaluated in the country.     

A medium to enhance identification of Septoria musiva from poplar cankers

A series of experiments was conducted to determine the relative tolerance in vitro of an isolate of Septoria musiva (a fungus that causes a severely damaging stem canker disease of poplars) for selected chemicals. Inhibition of diameter growth of this fungus on a V‐8 vegetable juice‐based medium with captan, chlorothalonil, iprodione, mancozeb and streptomycin sulphate at concentrations, respectively, of 50, 1, 10, 10, and 100 mg l^–1 was relatively low compared to inhibition of eight other fungi cultured from cankers on poplars. In addition, the presence of captan stimulated profuse sporulation of the fungus. These properties assisted in the identification of S. musiva from cankers resulting from artificial inoculation of poplar branches in the field.     

Genetic differences between autochthonous and breeding populations of common cypress (Cupressus sempervirens L.) in Greece

Individuals were selected for resistance against the imperfect fungus Seiridium cardinale Wag in six common cypress populations (Cupressus sempervirens L.) in Greece. A total of 109 resistant clones and 140 trees from their base populations were surveyed at several allozyme loci. The comparison yielded information on changes in genetic variation due to artificial selection. The genetic structure of the breeding populations was similar to their base populations. Nevertheless, the number of rare alleles among the resistant clones had decreased, showing a similar trend at most loci and for most comparisons. Possible implications for breeding strategies are discussed.     

Pre‐ and post‐inoculation water stress affects Sphaeropsis sapinea canker length in Pinus halepensis seedlings

In order to assess the influence of water stress on the development of Sphaeropsis sapinea cankers in Pinus halepensis, the stems of 4‐ to 5‐year‐old potted seedlings were artificially inoculated with the fungus before and after being kept at controlled water regimes from April 1997 to March 1998. In the pre‐water‐stress inoculation experiment, the canker length, measured 5 months after inoculation (September 1997), was greater in seedlings predisposed to extreme water deficit (midday needle water potential between ?4.5 and ?5.5 MPa). In the post‐water‐stress inoculation experiment, the fungus was inoculated in April 1998, after irrigation had enabled the seedlings to resume normal needle water potential. In this case also, at 5 months after inoculation, longer cankers were visible in seedlings that had been subjected to extreme water deficit. These findings suggest that the occurrence of marked water stress, although apparently tolerated by Aleppo pine, can enhance the development of S. sapinea cankers in this species, regardless of whether the stress occurs before or after infection by the fungus.     

High genetic diversity of Fusarium circinatum associated with the first outbreak of pitch canker on Pinus patula in South Africa

The disease known as pitch canker results from infection of Pinus species by the fungus Fusarium circinatum. This fungus also causes a serious root disease of Pinus seedlings and cuttings in forestry nurseries. Pinus radiata and P. patula are especially susceptible to the pathogen, but there are no records of pitch canker on P. patula in established plantations. To date, only planting material of this tree species in nurseries or in plantations at the time of establishment have been infected by F. circinatum. Symptoms of pitch canker have recently emerged in an established P. patula plantation in South Africa and this study sought to determine whether the symptoms were caused by F. circinatum. Isolates from cankers were identified as F. circinatum using morphology and DNA-based diagnostic markers. Microsatellite markers were then used to determine the genetic diversity of a collection of 52 isolates. The entire population included 17 genotypes representing 30 alleles, with a greater number of genotypes collected from younger (three- to six-year-old) than older (12- to 19-year-old) trees. Both mating types of F. circinatum were present, but no evidence of sexual recombination was inferred from population genetic analyses. This is the first record globally of pitch canker on P. patula trees in managed plantations. It is of significant concern to South Africa, where P. patula is the most important Pinus species utilised for plantation forestry.     

The first record of Botryodiplodia canker in Poland

This study describes the first observation of Botryodiplodia canker in the Western Carpathians in south‐eastern Poland caused by Botryodiplodia hypodermia (Sacc.) Petr. (syn. Sphaeropsis hypodermia, S. ulmicola). The canker occurred on an approximately 17‐year‐old Ulmus glabra sapling in a mixed conifer/deciduous stand with elm trees severely damaged by Dutch elm disease. This paper describes disease symptoms and provides information on the macro‐ and micromorphology of the fungus isolated from the cankered tissues. The results of BLAST search using DNA sequences obtained for our cultures and subsequent phylogenetic positioning of the fungus among closely related Botryosphaeriaceae indicate that the species is much more closely related to Phaeobotryon than to the other Botryodiplodia or Sphaeropsis species. Moreover, a total of 16 polymorphisms within the ITS region were detected between S. ulmicola associated with Botryodiplodia canker in North America and B. hypodermia associated with the canker observed in Poland. Thus, the “European” variant of “Sphaeropsis” ulmicola can now be easily identified with our barcode sequences. The Botryodiplodia canker is much less prevalent in Europe than in North America. Differences in virulence of “American” and “European” linages and differences in susceptibility of various elm species may be the reason for the higher prevalence of the disease in North America.     

Seiridium cardinale cankers in a tolerant Cupressus sempervirens clone under naturally CO2‐enriched conditions

Ramets of the Cupressus sempervirens clone Bolgheri were raised in three CO₂ concentrations in a naturally CO₂‐enriched environment [360 (control), 680 and 1670 μmol mol^–1 CO₂]. Bolgheri is patented as resistant to Seiridium cardinale. The ramets were artificially inoculated using a virulent isolate of S. cardinale. Healing of the resulting cankers was visually assessed over 6 years. Six months after inoculation, cankers on trees grown at 680 μmol mol^–1 were significantly larger than the controls. However, no significant trend was recorded at later dates. In conclusion, the Bolgheri clone maintained its resistance to S. cardinale and could be used to control cypress canker even in increasing atmospheric CO₂ concentrations.     

Variation in pitch canker resistance among provenances of <Emphasis Type="Italic">Pinus patula</Emphasis> and <Emphasis Type="Italic">Pinus tecunumanii</Emphasis> from Mexico and Central America

Pinus patula and high-elevation (HE) sources of P. tecunumanii exhibit intermediate levels of resistance to pitch canker (Fusarium circinatum), compared to extremely resistant species such as P. oocarpa, and extremely susceptible species such as P. radiata. Seedlings from 20 P. patula provenances and 15 HE P. tecunumanii provenances were artificially inoculated with the pitch canker fungus at 21 and 12 weeks of age, respectively, and assessed for resistance 12–20 weeks later. There was important provenance variation in pitch canker resistance for both species. The 20-week LiveStem percentage ranged from 70.3% to 43.6% among the P. patula provenances and 59.6% to 11.7% among HE P. tecunumanii provenances. There was a geographic pattern to the provenance variation, and in both species, low altitude sources demonstrated more resistance than those from high elevation. Provenance variation in pitch canker resistance could be useful when making selection and breeding decisions with these species.     

Genetic variation in dieback resistance in Fraxinus excelsior confirmed by progeny inoculation assay

Ash dieback caused by the pathogenic fungus Hymenoscyphus fraxineus [previously known as H. pseudoalbidus (sexual stage) and Chalara fraxinea (asexual stage)] is a widespread problem in Europe. Here, we assess crown damage from natural infection and necrosis development following artificial controlled inoculations on full‐sib and half‐sib progeny from Danish Fraxinus excelsior clones with contrasting and well‐characterized levels of susceptibility to the disease. The inoculation assay was performed on a total of 123 offspring, and necrosis development monitored over two years. The offspring from low susceptible mother clones developed smaller necroses when compared to offspring from susceptible clones. Their crown damage due to natural infections was also significantly less. The correlation coefficient between average crown damages of mother clones and the average of their progeny was 0.85 (natural infections), while the correlation between crown damage of mother clones and the average necrosis development in their progeny after controlled inoculation was 0.73. The correlation between resistance of parent trees and crown damage/necrosis development on their offspring confirms the presence of heritable resistance and indicates that a bioassay based on controlled inoculations has the potential of becoming a fast and cost‐effective tool for estimation of dieback susceptibility in breeding programmes for resistance in ash trees.