Della Rocca, G., Eyre, C. A., Danti, R., and Garbelotto, M. 2011. Sequence and simple-sequence repeat analyses of the fungal pathogen Seiridium cardinale indicate California is the most likely source of the cypress canker epidemic for the Mediterranean region. Phytopathology 101:1408-1417. Seiridium cardinale is the pathogenic fungus of unknown origin responsible for a world pandemic known as cypress canker affecting several species of Cupressaceae in both the Northern and Southern Hemisphere. In this study, a comparative genetic analysis of worldwide populations was performed using sequence analysis of a portion of the βtubulin locus and seven polymorphic simple-sequence repeat (SSR) loci on 96 isolates. Sequence analysis identified two distinct β-tubulin alleles, both present in California. Only one of the two alleles was detected in the Mediterranean basin, while two isolates from the Southern Hemisphere were characterized by the presence of the allele absent from the Mediterranean. SSRs identified a total of 46 multilocus genotypes (MGs): genotypic diversity was always higher in the California population, and calculations of the index of association (IA) determined the presence of linkage disequilibrium associated with the absence of sexual reproduction only in the Mediterranean population but not in California. In 50 instances, the same MG was found at great geographic distances, implying a role played by humans in spreading the disease. Network analysis performed on SSR data identified three clusters of MGs: California, Morocco, and the rest of the Mediterranean. Both the Morocco and the Mediterranean clusters were linked to the California cluster. Coalescent analysis identified insignificant migration between California and Italy, as expected in the presence of a single introduction event, and very high migration from Italy into Greece, as expected of an outbreak still in exponential growth phase and starting from an Italian source.

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Sequence and simple-sequence repeat analyses of the fungal pathogen Seiridium cardinale indicate California is the most likely source of the cypress canker epidemic for the Mediterranean region.

Common cypress (Cupressus sempervirens L.) is an integral feature of the landscape of many Mediterranean regions (particularly in Tuscany). Furthermore, common cypress has multiple uses as ornament, timber, windbreaks, recovery of deteriorated soils, protection of slopes and the production of essential oils. During the last three decades, Seiridum cardinale canker of cypress has caused severe losses in woods, windbreaks and ornamental plantings in the Mediterranean area, significantly limiting the use and cultivation of this tree. In this paper we describe 'Italico' and 'Mediterraneo', two C. sempervirens varieties which were patented in 2004 for their resistance to cypress canker. Both varieties are particularly suitable for ornamental purposes because of their fastigiated columnar habit and the low production of male flowers and cones. 'Italico' and 'Mediterraneo' represent the recent result of the breeding programme on cypress, in progress since the 1970s. This program aims at: 1) obtaining a high number of canker-resistant cypress clones and multi-clonal varieties to be used for ornamental plantings and windbreaks and 2) finding mother trees for the production of improved seed for reforestation purposes.

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'Italico' and 'mediterraneo' : Two Seiridium cardinale canker-resistant cypress cultivars of Cupressus sempervirens

The use of tissue culture methodologies for studies of pathogen physiology, host vs. pathogen interrelationships and disease resistance has a short but productive history in agronomy and horticulture (23, 44, 45). The very recent applications of these procedures for forest trees show tremendous potential to circumvent some of the difficult logistical problems of studying disease in vivo. Technical and informational gains made in other plant sciences are now being examined by forest pathologists to supplement and accelerate traditional breeding programs (60, 66).

Tissue Culture Application to Forest Pathology and Pest Control

Canker stain, caused by the fungus Ceratocystis platani, is a destructive disease in Platanus spp. It has been recently proved that resistant accessions can be produced and grown in Europe. However, additional resistant genotypes are still needed in order to avoid the onset of virulent pathogen strains favoured by the selection pressures exerted by genetically homogeneous resistant plane tree plantings. In this study we present the results of two parallel experiments performed on 975 accessions of P. × acerifolia seedlings and P. × acerifolia clones derived by cutting propagation from mature trees grown in the urban environments. The selection process was based on inoculation with C. platani and yielded 13 accessions that showed different types of resistant reactions and survived in a stable manner thoughout the period of observation. Selected accessions were characterised by sequencing the rDNA-ITS region and by developing PCR procedures capable of detecting P. orientalis and P. occidentalisLEAFY homoeologues. These molecular analyses enabled us to confirm the identification of the species, its hybrid origin and to assess an evident genetic variability among the accessions, which therefore have to be considered as different genotypes.

Platanus × acerifolia genotypes surviving to inoculation with Ceratocystis platani (the agent of canker stain): first screening and molecular characterization

Summary

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.

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

Ramets of 200 clones of Cupressus sempervirens were inoculated with 6 isolates of Seiridium cardinale. No significant differences were found among isolates, while there were highly significant differences among clones when length and width of canker were assumed as discriminating traits.

A. Panconesi

Papers

Pathogenicity of some isolates of Seiridium (Coryneum) cardinale, agent of cypress canker disease