No abstract

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.

Seiridium cardinale is regarded as the most important agent responsible for the disease of cupressaceous hosts referred to as Cypress canker. The fungus was first described in California and is currently reported in all continents. A recent study based on seven SSR loci has suggested that California populations may represent the source of the epidemic in the Mediterranean. In this study, 185 AFLP markers were used on an expanded sample size of 125 isolates to determine whether the Mediterranean population may indeed be derived from the California one and to compare the reproductive modes of populations in the two regions of the world. Additionally, AMOVA, NJ, STRUC-TURE, principal component analysis and b-tubulin sequence analyses were employed to infer the presence of genetic structure within and between populations. The distribution of pairwise AFLP similarity coefficients suggests Mediterranean populations are reproducing only clonally, while California populations are reproducing both clonally and sexually. AMOVA indicates Mediterranean and California populations are currently genetically isolated, but NJ and STRUCTURE analyses both suggest ancestral Mediterranean genotypes belong to the California population. No alleles were private to either population, and the presence of identical or quasi-identical genotypes at large distances supports the notion that movement of infected cypress plants is responsible for the global spread of the disease. Surprisingly, STRUCTURE identified a second cluster of Mediterranean genotypes distinct from the basal mixed California-Mediterranean cluster. This second cluster either may have originated from the first one under the selection pressure imposed on the pathogen in the new Mediterranean environments or may be the result of a further introduction from California or elsewhere. Cumulatively, the evidence presented here suggests that S. cardinale may be native or long naturalized in California and that two genetically distinct groups are present in the Mediterranean, with obvious implications for further studies on this disease.

Stem cankers and branches showing bark discoloration, fissuring, resin exudation leading to dieback, crown wilting, and tree mortality have been observed since late spring 2008 on 40-year-old Cupressus macrocarpa (Hartw.) trees planted in forests mixed with Juniperus oxycedrus L. and Acer monspessulanum L. in Taffet, near Ain Abbessa, in the district of Bougaa, Algeria (36°18′57″N; 05°06′33″E; 1,400 m elevation). In 2010, approximately 60% of the C. macrocarpa trees were diseased. For fungal isolations, cankered branches were surface sterilized with ethanol. After removal of the outer bark, fragments of necrotic inner bark taken from the margin of cankers were plated on potato dextrose agar (PDA). Most of the colonies were identified as Botryosphaeria iberica (Phillips, Luque & Alves) based on comparison of morphological traits and DNA sequences with known isolates of the fungus (1). Pestalotiopsis funerea colonies were also obtained, although with less frequency. B. iberica colonies on PDA were dark green with aerial mycelium and optimum growth at 25°C. Pycnidia were produced after 3 weeks of incubation at 20°C under a 12-h near UV light photoperiod on water agar amended with autoclaved cypress seeds. Conidia were brown, one-septate, oval to oblong, and 24.2 (20.1 to 27.4) × 11.2 μm (8.8 to 14.1) (n= 50). An isolate was deposited at the Centralbureau voor Schimmelculture as CBS 130984. DNA was extracted from freeze-dried mycelium and amplified using primers ITS1 and ITS4. The amplified DNA sequence of B. iberica isolate CBS 130984 from Algeria (GenBank Accession No. JN836991) showed 100% homology with sequences of B. iberica isolates obtained from dead and cankered bark of oaks from Spain and Italy (GenBank Accession Nos. AY573216, AY573214, AY573213, AY573210, AY573202, and AY573201). Stem inoculations were performed in the greenhouse on 10 4-year-old, grafted plants of C. macrocarpa growing in 5-liter pots using isolate CBS 130984. A 3-mm plug taken from the margin of a colony grown on PDA for 1 week was inserted in a circular wound of the same size made in the bark with a cork borer where the stem diameter was approximately 1 cm. Inoculations were repeated in June 2010 and June 2011. Five months after inoculations, small rounded to elongated lesions (1.0 to 2.5 cm long), sometimes with resin exuding cracks, were visible on all inoculated stems. Control trees, inoculated with sterile PDA plugs, showed no canker development. B. iberica was successfully reisolated from the necrotic bark surrounding the inoculation sites. No significant differences in canker size were observed between the two replicated experiments. Some Botryosphaeria species that are found on a variety of hosts are also known to cause cankers and dieback of cypress; among these are B. stewensii, B. obtusa, B. dothidea, and B. ribis, often acting as weak pathogens (2,3). Considered weakly virulent in causing dieback of grapevine (4) and, to our knowledge, reported here for the first time on Cupressaceae, B. iberica caused cankers and dieback of C. macrocarpa trees that had probably been weakened by repeated drought events occurring in Algeria during the last 10 years. References: (1) A. Phillips et al. Mycologia 97:513, 2005. (2) E. Punithalingam and J. M. Waller. IMI Descriptions of Fungi and Bacteria 40, Sheet 394, 1973; (3) E. Punithalingam and P. Holliday. IMI Descriptions of Fungi and Bacteria. 40, Sheet 395, 1973; (4) R. Úrbez-Torres et al. Plant Dis. 93:584, 2009.

Leyland cypress (× Hesperotropsis leylandii) is a fast-growing conifer used in most temperate regions as an ornamental tree for hedges and screens, and is one of the most commercially important trees in Europe. In recent years, severe diebacks and mortality due to cypress canker have been observed on Leyland cypress plantations in Southern Europe. This study was conducted to evaluate (i) the spread and impact of cypress canker caused by Seiridium cardinale in plantations of a sample area of 1,250 km2 in central Italy, (ii) the response of the most commonly grown Leyland cypress varieties to artificial inoculation with to S. cardinal, and (iii) the pathogenicity of S. cardinale isolates obtained from Leyland cypress. Of the 1,411 surveyed trees, 11.4% had been killed by cypress canker and 43.9% of the living trees were affected by the disease. The number of diseased or dead trees and the percentage of cankered trunks was significantly correlated with the mean trunk diameter of the plantations. Six months after inoculation, the size of developed cankers was significantly different among the inoculated Leyland cypress cultivars but all of them showed markedly larger cankers than the C. sempervirens canker-resistant control clone. All of the tested S. cardinale isolates obtained from Leyland cypress also caused cankers on Cupressus sempervirens when inoculated as conidial suspensions or mycelia. Leyland cypress is highly prone to contract cypress canker in the Mediterranean due to its high susceptibility to S. cardinale infections, low genetic variability among the grown cultivars, and cracks which form on fast-growing trunks, favoring entry of the fungus into the inner bark and the occurrence of infections.