G. Polizzi

Root and Collar Rot of Milkwort Caused by Cylindrocladium pauciramosum, a new record for Europe

A new disease of milkwort (Polygala myrtifolia) was observed on several commercial nurseries in southern Italy. Diseased plants showed wilting, stunting, chlorosis or loss of foliage, and rotting of the basal stem as well as the crown and roots. A Cylindrocladium species was consistently found associated with crown, basal stem, and root lesions. The etiology of this disease was proved on milkwort, by fulfilling Kochs postulates. Two hundred Cylindrocladium isolates were collected from the most important Sicilian and Calabrian ornamental production areas from different host plants. Isolates were identified as Cylindrocladium pauciramosum (teleomorph Calonectria pauciramosa) on the basis of their obpyriform to broadly ellipsoidal terminal vesicles, conidiophore branching pattern, conidium morphology, as well as mating type studies with tester strains of C. pauciramosum for selected isolates. This is the first record of this pathogen from Europe and it is the first report of C. pauciramosum on milkwort.

Evaluation of Trichoderma harzianum strain T22 as biological control agent of Calonectria pauciramosa

The objective of this research was to evaluate Trichoderma harzianum strain T22 as a biocontrol agent of collar and root rot caused by different Calonectria pauciramosa isolates. Thus, the microsclerotia-forming ability and virulence of twenty C. pauciramosa isolates were assessed. Microsclerotia production varied partially among the isolates and dual culture with T22 on carnation leaf agar revealed isolates with both high and low microsclerotia-forming ability. Inoculation tests on red clover (Triflolium pratense) demonstrated its susceptibility to the pathogen. On red clover, the degree of virulence and T22 effects in controlling infections were highly variable among the isolates tested. A nursery trial performed on Feijoa sellowiana seedlings confirmed previous results, clearly indicating virulence variability among C. pauciramosa isolates. For three isolates tested in nursery trial, T22 effectiveness in controlling infection was inversely related to their degree of virulence. Overall, T. harzianum strain T22 showed good antagonist activity in reducing microsclerotia production on carnation leaf and the incidence and severity of collar and root rot on both selected hosts. This data could be crucial in developing integrated pest management strategies in ornamental plant nurseries.

Calonectria spp. causing leaf spot, crown and root rot of ornamental plants in Tunisia.

Calonectria spp. are important pathogens of ornamental plants in nurseries, especially in the Northern Hemisphere. They are commonly associated with a wide range of disease symptoms of roots, leaves and shoots. During a recent survey in Tunisia, a number of Calonectria spp. were isolated from tissues of ornamental plants showing symptoms of leaf spot, crown and root rot. The aim of this study was to identify these Calonectria spp. using morphological and DNA sequence comparisons. Two previously undescribed Calonectria spp., C. pseudomexicana sp. nov. and C. tunisiana sp. nov., were recognised. Calonectria mexicana and C. polizzii are newly reported for the African continent. Pathogenicity tests with all four Calonectria spp. showed that they are able to cause disease on seedlings of Callistemon spp., Dodonaea viscosa, Metrosideros spp. and Myrtus communis.

Reduction of Corky Root Infections on Greenhouse Tomato Crops by Soil Solarization in South Italy

Five greenhouse experiments were conducted in southeastern Sicily (Italy) from 2000 to 2009 to evaluate the effectiveness of soil solarization in reducing natural infections of tomato corky root caused by Pyrenochaeta lycopersici. Tests were performed with clear, traditional, and innovative plastic films and fumigant applications. In all the trials, soil solarization was effective in controlling corky root disease relative to an untreated control. Although inducing different thermal regimes in the soil, the use of different greenhouse covering and mulching films for solarization proved effective in reducing corky root severity relative to the untreated control. Solarization reduced infections caused by P. lycopersici comparable with methyl bromide fumigation and greater than metham sodium and metham potassium. Among the tested films, green coextruded film may be most attractive because it can be left on after solarization as mulch.

First Record of Crown and Root Rot Caused by Cylindrocladium pauciramosum on Brush Cherry in Italy

Brush cherry (Eugenia myrtifolia Sims; synonym Syzygium paniculatum Gaertn.) is a woody evergreen ornamental plant belonging to the Myrtaceae family. This plant is a very common species in Sicilian landscapes. In June of 2008, a new blight disease was detected in a commercial nursery located in Sicily (Italy) in a stock of 10,000 2-year-old E. myrtifolia cv. Newport potted plants obtained from cuttings. The disease was randomly distributed, affecting approximately 2% of the plants. Twig dieback, followed in some cases by plant death, was associated with crown and root rot. Roots were necrotic and crown tissue was brown. A Cylindrocladium sp. was consistently isolated from symptomatic roots, crowns, and lower stems of affected plants on potato dextrose agar petri dishes. Phytophthora isolates were not found associated with symptomatic tissues with BNPRAH (benomyl, nystatin, pentachloronitrobenzene, rifampicin, ampicillin, and hymexazol) selective medium. Five Cylindrocladium isolates were selected and subsequently identified as single-conidial colonies on carnation leaf agar. Isolates were incubated at 25°C under near-UV light with a 12-h_light/dark regimen and examined after 7 days (1). Isolates were characterized by having conidiophores terminating in obpyriform to broadly ellipsoidal vesicles and conidia hyaline, one septate, and straight with rounded ends, (50-) 54 to 55 (-59) × (3.5-) 4 to 6 μm. These characteristics, as well as their ability to produce perithecia when mated with Italian tester strains of Cylindrocladium pauciramosum, allowed their identification as C. pauciramosum C.L. Schoch & Crous (1,4). One mating type (MAT1-1) was found to be present on this host and a representative fungal isolate (DISTEF-Em3) was deposited at the Centraalbureau voor Schimmelcultures (CBS) open fungi collection (Fungal Biodiversity Centre, Utrecht, NL) with Accession No. 123917. Pathogenicity of the isolate DISTEF-Em3 was confirmed by applying 10 ml of a spore suspension (105 conidia per ml) to the crowns of 20 potted 4-month-old E. myrtifolia cv. Newport cuttings that were subsequently maintained in a greenhouse (23 to 25°C and 80 to 90% relative humidity). The same number of untreated plants was used as control. After 4 weeks, only four treated plants developed symptoms identical to those observed in the nursery. Control plants remained symptomless. C. pauciramosum was always reisolated from the infected plants and the identification of the isolate was made as previously described. Pathogenicity tests were repeated twice. In Italy, C. pauciramosum is a widespread pathogen in nurseries that causes extensive losses on young ornamental plants belonging to several genera (2,3). On the basis of the limited spread of the disease in the nursery and the pathogenicity tests, we consider Cylindrocladium crown and root rot of brush berry as a minor disease. However, this work demonstrated the susceptibility of brush cherry to C. pauciramosum that could lead to more extensive losses in association with other biotic or abiotic stresses. To our knowledge, this is the first record of crown and root rot caused by C. pauciramosum on brush cherry. References: (1) P. W. Crous. Taxonomy and Pathology of Cylindrocladium (Calonectria) and Allied Genera. The American Phytopathological Society, St. Paul, MN, 2002. (2) G. Polizzi et al. Plant Dis. 85:803, 2001. (3) G. Polizzi et al. Plant Dis. 90:1459, 2006. (4) C. L. Schoch et al. Plant Dis. 85:941, 2001.

First Occurrence of Calonectria Leaf Spot on Mexican Blue Palm in Italy

In April 2006, a new leaf disease occurred in a private garden in eastern Sicily (Italy) on young, 2-year-old seedlings of Mexican blue palm, Brahea armata S. Watson, in the Arecaceae. Symptoms were detected on 80% of seedlings. The leaves had minute, brown spots that enlarged into dark brown, circular or elliptical lesions, 3 to 6 mm in diameter, and with a necrotic, gray center. The lesions sometimes were surrounded by a chlorotic halo, and older leaves had larger chlorotic areas between spots. Conidia, conidiophores, and terminal vesicles were examined from diseased leaves. A Cylindrocladium sp. was consistently isolated from leaf lesions on Oxoid (Basingstoke, Hampshire, England) potato-dextrose agar after surface disinfestations with 0.8% NaOCl. Cylindrocladium isolates were cultured on carnation leaf agar (CLA) using single hyphal tips. Five isolates were established and identified as Calonectria pauciramosa C.L. Schoch & Crous based on obpyriform to broadly ellipsoidal terminal vesicles, conidiophore branching pattern, conidia size (52 × 4.6 μm), perithecium morphology, and ascopores size (36 × 6.8 μm). Perithecia were obtained with C. pauciramosa tester strains from Italy (G87 and G128) and South Africa (U 971 and U 1670) (2,3) that confirmed both mating types to be present. Further confirmation was obtained by internal transcribed spacer (ITS) analysis. The sequence of rDNA ITS1-5.8 S-ITS2 regions, obtained after amplification with primer ITS1 and ITS4, revealed that the Brahea isolates showed total homology with the sequence of the C. pauciramosa (STE-U 971 from soil) (= Cylindrocladium pauciramosum) available in GenBank. Isolate CBS 120619 from Mexican blue palm was deposited at Centraalbureau voor Schimmelcultures. Spray inoculations of 10 2-year-old Mexican blue palm seedlings were performed with a spore suspension of the fungus adjusted to 105 conidia per ml obtained from 14-day-old single-spore colonies on CLA at 24°C under cool white fluorescent irradiation on a 12-h light/dark regimen. In addition, the following species were similarly inoculated using 10 1-year-old plants: Arecastrum romanzoffianum (Cham.) Becc., B. edulis H. Wendl. ex S. Watson, Chamaerops humilis L., Howea forsteriana Becc., Phoenix canariensis Hort. ex Chabaud., Trachycarpus fortunei (Hook.) H. Wendl., and Ravenea rivularis Jumelle & Perrier. Inoculated, and 10 control plants were placed in separate plastic bags in a growth chamber at 25 ± 1°C. After 7 to 10 days, foliar symptoms including flecks and spots developed on both species of Brahea and on Chamaerops humilis, and on these hosts, pathogenicity tests were repeated. Other palm species and control plants remained healthy. C. pauciramosa was consistently reisolated from inoculated plants on the basis of vesicle shape and conidia sizes of the anamorph. Cylindrocladium candelabrum, Cylindrocladium colhounii, Cylindrocladium floridanum, Cylindrocladium parasiticum, Cylindrocladium pteridis, Cylindrocladium scoparium, and Cylindrocladium theae have been reported as leaf spots pathogens of Arecaceae (1). To our knowledge, this is the first occurrence of C. pauciramosa on Mexican blue palm and the first report of the pathogen on Arecaceae. References: (1) P. W. Crous. Taxonomy and Pathology of Cylindrocladium (Calonectria) and Allied Genera. The American Phytopathological Society, St. Paul MN, 2002. (2) P. W. Crous et al. Stud. Mycol. 50:415, 2004. (3) G. Polizzi and P. W. Crous Eur. J. Plant Pathol. 105:407, 1999.

First record of crown and root rot caused by Cylindrocladium pauciramosum on California lilac in Italy.

California lilacs, or Ceanothus, are evergreen, drought tolerant, colorful ornamental shrubs belonging to the Rhamnaceae family. Ceanothus thyrsiflorus var. repens is the most common species grown in Italy. In October 2005, a severe wilting was noticed on approximately 3,000 potted, 6-month-old plants obtained from cuttings produced by a commercial nursery in Lecco Province (northern Italy). Wilting was always associated with root rot and brown discoloration at the base of the stem. No leaf spots or stem lesions were detected. A Cylindrocladium sp. was isolated consistently from crown, basal stems, and roots of symptomatic plants with potato dextrose agar. Although many crown rots are caused by Phytophthora spp., this pathogen was not found associated with rotten roots and crown plating small pieces of diseased root tissue and crowns onto selective medium. A random selection of five Cylindrocladium sp. isolates was obtained from the infected crown and basal stem. Subsequently, they were identified on carnation leaf agar (CLA) as Cylindrocladium pauciramosum C.L. Schoch & Crous on the basis of their obpyriform to broadly ellipsoidal terminal vesicles, conidiophore branching pattern, conidium, and perithecial morphology, as well as mating type with tester strains of C. pauciramosum selected isolates (1,4). All single-conidial isolates were mated with tester strains DISTEF-G87 (MAT1-1) and DISTEF-G128 (MAT1-2) of C. pauciramosum on CLA, which confirmed both mating types to be present. Two of the isolates were deposited at Fungal Biodiversity Centre, Centraalbureau voor Schimmelcultures (CBS-120145 and CBS-120146). Pathogenicity tests were performed by macerating CLA cultures of C. pauciramosum, obtained from a single-spore isolate and incorporating them on the soil surface of 20 8-month-old C. thyrsiflorus var. repens potted plants. The same number of plants was used as the control. Following inoculation, plants were well irrigated and kept in a growth chamber at 25 ± 1°C. All inoculated plants developed crown rot, basal stem rot, and root rot 25 days after inoculation. Uninoculated control plants remained healthy. C. pauciramosum was reisolated from the artificially inoculated plants. C. pauciramosum causes considerable damage to the ornamental industry in Italy, where projects have been carried out since the first record of the fungus in Europe (3). C. pauciramosum was previously detected on Ceanothus sp. in the United Kingdom (2), where foliar and stem lesions were described. To our knowledge, this is the first record of the pathogen on C. thyrsiflorus var. repens and the first report of wilting due to crown and basal stem rot. References: (1) P. W. Crous. Taxonomy and Pathology of Cylindrocladium (Calonectria) and Allied Genera. The American Phytopathological Society, St. Paul MN, 2002. (2) C. R. Lane et al. Plant Pathol. 55:582, 2006. (3) G. Polizzi and P. W. Crous. Eur. J. Plant Pathol. 105, 407, 1999. (4) C. L. Schoch et al. Plant Dis. 85:941, 2001.

Postharvest efficacy of resistance inducers for the control of green mold on important Sicilian citrus varieties

The disease reducing activity of acibenzolar-S-methyl (ASM), chitosan and β-aminobutyric acid (BABA) against postharvest green mold (GM) of citrus fruit, Penicillium digitatum, was investigated by tests performed in in vitro and in vivo conditions. The inhibition of the mycelial growth of P. digitatum by ASM, chitosan and BABA at different concentrations was evaluated on potato dextrose agar and on orange peel extract agar. The pathogen was totally inhibited (100% growth inhibition) by chitosan at concentrations ≥ 0.1% and by BABA at 1000 mmol and only poorly inhibited by ASM at 0.5% (47% growth inhibition). Inhibitory effects of chitosan and BABA were confirmed by P. digitatum conidial germination tests. The performances of these chemical compounds were evaluated in vivo on artificially inoculated orange, lemon and grapefruit cultivars. On the whole, chitosan significantly reduced GM decay on ‘Valencia’ and ‘Washington Navel’ orange, ‘Femminello’ lemon and grapefruit cv. Marsh Seedless at the concentration of 0.5% (6–20% disease incidence), and BABA provided the best results on ‘Tarocco Scirè’and ‘Valencia’ orange and grapefruit cv. Marsh Seedless at the concentration of 1000 mmol (12–16% disease incidence). ASM did not show any efficacy. This study demonstrated that the effects of chitosan and BABA on GM in citrus fruits may be associated with their direct fungitoxic properties against the pathogen. Treatments with chitosan and BABA could be recommended for inclusion in postharvest decay management programs for citrus packinghouses and their use may be an effective method to improve the integrated pest management strategy.

Characterisation and pathogenicity of Pestalotiopsis uvicola and Pestalotiopsis clavispora causing grey leaf spot of mango (Mangifera indica L.) in Italy

During 2009 and 2010, twenty-one isolates of Pestalotiopsis spp. Associated with grey patches on the leaves, twigs, and panicles of mango were collected in six orchards located in Sicily (Italy). Morphological characteristics of colony (colour and mycelium appearance), and conidia (size, shape, septation, length and the number of apical and the basal appendages) as well as phylogenetic analysis of the Internal Transcribed Spacer (ITS) region (ITS1, 5.8S gene, and ITS2) of six representative isolates revealed the occurrence of P. uvicola and P. clavispora. The representative isolates of both species were pathogenic to the artificially inoculated detached mango leaves cv. Kensington Pride and showed significant variation in lesion size. This is the first report worldwide of P. uvicola and P. clavispora causing grey leaf spot of mango.

Occurrence and Pathogenicity of Pseudomonas Fluorescens and P. Putida on Tomato Plants in Italy

SUMMARY During 2006-2008, a survey conducted in soilless and soil-grown tomato crops in eastern and southeastern Sicily (Italy) disclosed the presence of widespread leaf chlorosis and necrosis associated with yellow, pink or brown discolouration of vascular and pith tissues. Bacteria were always isolated from symptomatic tissues on KB and NA media. A total of 158 isolates showed the LOPAT characters of group Va (-+-+-) and group Vb (++-+-) and 21 of these strains were identified as different biovars of Pseudomonas fluorescens and P. putida. Koch’s postulates showed that 42 fluorescent Pseudomonas isolates are able to induce vascular discolouration of tomato plants but not leaf chlorosis and necrosis. The interactions of vascular infections and abiotic stresses were studied in growth chamber experiments. Differences in virulence were found among P. fluorescens biovar I and P. putida bv. A strains on tomato plants grown under saline stress conditions. Both bacteria were able to induce leaf chlorosis, necrosis or death of tomato plants under saline stress conditions.