Fungal Species Causing Canker and Wilt of Ficus carica and Evidence of their Association with Bark Beetles in Italy

Field surveys conducted during 2021 and 2022 in Western Sicily, Italy, revealed the presence of common fig trees severely affected by trunk and crown root canker and bark cracking. Moreover, in conjunction with the symptomatic tissues, the same surveyed plants showed the presence of bark beetle holes and internal wood galleries. The predominant beetle Criphalus dilutus was previously reported attacking figs in Sicily. Phylogenetic analyses based on multi-locus DNA data showed the presence of different fungal taxa associated with disease symptoms, including Botryosphaeria dothidea, Ceratocystis ficicola, Diaporthe foeniculina, Neocosmospora bostrycoides, N. perseae and Neofusicoccum luteum. Pathogenicity tests conducted on potted fig plants showed that all the species were pathogenic to fig, with C. ficicola and Neocosmospora spp. as the most aggressive fungal species. Moreover, isolations conducted from the bodies of emerging adult insects recovered from disease samples confirmed the presence of C. ficicola and Neocosmospora spp., suggesting the potential involvement of C. dilutus in their dissemination.

A quantitative PCR assay for the detection and quantification of Septoria pistaciarum, the causal agent of pistachio leaf spot in Italy

Septoria leaf spot is one of the most widespread diseases affecting pistachio (Pistacia vera) in countries of the Mediterranean region. Septoria pistaciarum was recently confirmed as the causal agent of this disease in Italy. Currently, the detection of S. pistaciarum relies on isolation techniques. These require significant amounts of labor, and time for completion. Also, a reliable identification requires the sequencing of at least two housekeeping genes, in addition to the morphological observations. To accurately detect the presence and quantify S. pistaciarum in pistachio tissues, a molecular tool was necessary. We designed applicable primers that allow reliable amplification of the β-tubulin gene. The amplification of target DNA was highly efficient, with a 100% success rate, and the assay was able to detect as little as 100 fg/rxn of pure fungal DNA. When tested in artificial mixtures of plant and pathogen DNAs, the assay was able to detect the pathogen consistently at a limit of detection of 1 pg/rxn. The assay was also effective in identifying the pathogen in naturally infected samples, providing rapid detection in all symptomatic specimens. The resulting qPCR assay is an improved detection tool for accurate diagnosis of S. pistaciarum that can also contribute to better understand the population dynamics of the pathogen in the orchard.

First report of seedling stem blight of mango caused by Neofusicoccum parvum in Italy

Seedling blight of mango (Mangifera indica L.) was observed in a commercial nursery located in Messina province (eastern Sicily, Italy) during winter of 2021. More than 30% of 3,000 seedlings, about three to six months old, of mango cv. Gomera 3 showed symptoms of basal stem blight. The symptoms started from seed, led to the decline and subsequent death of the plants. Necrotic lesions appeared at crown level two months after sowing. The stem tissues of ten symptomatic plants were cut, surface sterilized, dipped in 1.5% sodium hypochlorite for 1 min and transferred onto potato dextrose agar medium (PDA) and incubated at 25°C for four days. Approximately 60% of stem tissues developed very similar fungal colonies, resembling to Botryosphaeriaceae. A total of four representative isolates were collected through single hyphal-tip and stored at 4 °C. The internal transcriber spacer region (ITS) was amplified with primers, ITS5/ITS4 (White et al., 1990), and EF1-728F and EF1-986R (Carbone and Kohn, 1999) were used to amplify part of the translation elongation factor 1alpha gene (tef1-α), and primers Bt2a/Bt2b (Glass and Donaldson, 1995) were used for the partial β-tubulin (tub2). The obtained sequences were deposited in GenBank with accession numbers: ON911292-95 for the ITS, ON933621-24 for tef1-α and ON933625-28 for tub2.To compare the results, 50 additional sequences were selected and inserted in the alignment according to the recent literature on the Botryosphaeriaceae (Bezerra et al., 2021; Zhang et al., 2021). Maximum parsimony analysis (MP) of concatenated dataset (ITS + tef1-α + tub2) was performed in PAUP v.4.0a. Clade support was assessed by 1,000 bootstrap replicates and Botryosphaeria dothidea was used as an outgroup. Our isolates clustered within the group of Neofusicoccum parvum (71% bootstrap value) (ex-type CMW9081). Based on these results, and morphological data (50 conidia length × width average: 18.1 × 6.6, respectively) our isolates (named MC) were identified and confirmed as Neofusicoccum parvum (Pennycook & Samuels) Crous, Slippers & A.J.L. Phillips. Pathogenicity tests were also conducted on 18 mango cv. Gomera 3 seedlings. The crown roots of each seedling were mechanically wounded and a mycelial plug of the isolate MC14 was placed onto them and covered with soil. Controls (three seedlings) were inoculated with sterile PDA only. Seedlings were maintained in a growth chamber with a 12 hrs photoperiod at 25°C ± 1°C and watered regularly. After five days, stem lesions appeared externally (1.6 cm) and one month after the inoculation, all the inoculated seedlings died. However, controls did not show any obvious symptoms. Re-isolations were conducted as described above and fulfilled Koch's postulates confirming pathogenicity. Among the diseases affecting mango plants, Botryosphaeriaceae represent a serious threat in Sicily as reported by Aiello et al., 2022. The endophytic behaviour of Botryosphaeriaceae is well known, making them latent pathogens (Slippers and Wingfield, 2007). In Italy, N. parvum was detected in mango orchards since 2013 (Ismail et al. 2013), but symptoms of seedlings stem blight have never been reported in the nursery. In Sicily, an increase of Botryosphaeriaceae infection has been observed recently, especially in nurseries, where N. parvum has been identified as a most destructive pathogen (Aiello et al., 2020; Gusella et al., 2021). To our knowledge, this is the first report worldwide of N. parvum causing mango seedling blight. The high incidence of infected seedlings detected in this study highlights the potential risk during propagation in the nursery, representing a significant source of inoculum for the field.

Effects of Temperature on Development of Canker-Causing Pathogens in Almond and Prune

Between 2000 and 2020, canker diseases of nut and stone fruit trees have become very widespread and severe in California. This study determined the effects of temperature on the development of canker-causing pathogens of almond and prune. Five pathogen taxa, Botryosphaeria dothidea, Cytospora leucostoma, Diaporthe (Phomopsis) neotheicola, Lasiodiplodia citricola, and Neofusicoccum mediterraneum, were used. Colony growth on medium and canker lesion development on detached shoots were measured at 10, 15, 20, 25, 30, and 35°C. The effects of temperature on colony growth differed among different pathogen taxa, although 25°C was the optimal temperature for most of the pathogens tested. The patterns of lesion growth as response to temperature were different among the different pathogens and tree crops. On almond, the highest growth rates appeared at 30°C for B. dothidea and L. citricola, but at 20°C for N. mediterraneum. The growth rates for C. leucostoma were lower than those of the other three pathogen taxa, with the highest rates recorded at 25°C. However, on prune, C. leucostoma showed greater lesion growth rates at different temperatures than the other pathogen taxa and maximum growth at 30 to 35°C. Similar trends were observed for L. citricola. The growth rates of B. dothidea and N. mediterraneum were comparatively lower than those of C. leucostoma and L. citricola.

Etiology of Botryosphaeria Panicle and Shoot Blight of Pistachio (Pistacia vera) Caused by Botryosphaeriaceae in Italy

Pistachio (Pistacia vera) is an important crop in Italy, traditionally cultivated in Sicily (southern Italy) for several decades now. In recent years, new orchards have been planted in new areas of the island. Field surveys conducted in 2019 revealed the presence of symptomatic trees showing shoot dieback, cankers, fruit spots, and leaf lesions. Isolations from symptomatic samples consistently yielded fungal species in the Botryosphaeriaceae family. Identification of collected isolates was conducted using morphological and molecular analyses. Morphological characterization was based on conidia measurements of representative isolates and also effects of temperatures on mycelial growth was evaluated. DNA data derived from sequencing the ITS, tef1-α, and tub2 gene regions were analyzed via phylogenetic analyses (maximum parsimony and maximum likelihood). Results of the analyses confirmed the identity of Botryosphaeria dothidea, Neofusicoccum hellenicum, and N. mediterraneum. Pathogenicity tests were conducted on detached twigs and in the fields both on shoots as well as on fruit clusters using the mycelial plug technique. The inoculation experiments revealed that among the Botryosphaeriaceae species identified in this study N. hellenicum (occasionally detected) and N. mediterraneum were the most aggressive based on lesion length on shoots and fruits. N. mediterraneum was the most widespread among the orchards while B. dothidea can be considered a minor pathogen involved in this complex disease of pistachio. Moreover, to our knowledge, this is the first report of N. hellenicum in Italy.

A New Disease for Europe of Ficus microcarpa Caused by Botryosphaeriaceae Species

The Indian laurel-leaf fig (Ficus microcarpa) is an important ornamental tree widely distributed in the urban areas of Italy. Surveys conducted in 2019 and 2020 on several tree-lined streets, squares, and public parks in Catania and Siracusa provinces (Sicily, southern Italy) revealed the presence of a new disease on mature trees. About 9% of approximately 450 mature plants showed extensive branch cankers and dieback. Isolations from woody tissues obtained from ten symptomatic plants consistently yielded species belonging to the Botryosphaeriaceae family. The identification of the recovered fungal isolates was based on a multi-loci phylogenetic (maximum parsimony and maximum likelihood) approach of the ITS, tef1-α, and tub2 gene regions. The results of the analyses confirmed the presence of three species: Botryosphaeria dothidea, Neofusicoccum mediterraneum, and N. parvum. Pathogenicity tests were conducted on potted, healthy, 4-year-old trees using the mycelial plug technique. The inoculation experiments revealed that all the Botryosphaeriaceae species identified in this study were pathogenic to this host. Previous studies conducted in California showed similar disease caused by Botryosphaeriaceae spp., and the pathogenic role of these fungi was demonstrated. To our knowledge, this is the first report of Botryosphaeriaceae affecting Ficus microcarpa in Europe.

Update of pistachio leaf spot caused by Septoria pistaciarum in light of new taxonomic advances in Italy

Septoria leaf spot is one the most widespread disease affecting pistachio (Pistacia vera) in countries of the Mediterranean region. Traditionally, three species have been associated with pistachio, including Septoria pistaciae, Septoria pistaciarum and S. pistacina. However, recent taxonomic studies have reordered and clarified the status of Septoria and septoria-like pathogens affecting pistachio. In our study, field surveys conducted in the traditional Sicilian pistachio production area of Bronte revealed the presence of trees showing characteristic septoria-like leaf spot. Collected isolates were morphologically and molecularly characterized. Morphological characterization was based on conidia measurements and evaluation of mycelial growth on different artificial media. Tested media included CMA, MEA, OA, PDA, and SNA. Phylogenetic analysis was conducted on a multi-locus approach (ITS + tef1 + tub2) based on Maximum Parsimony and Maximum Likelihood. Results showed that our isolates clustered with S. pistaciarum. Pathogenicity test was conducted in the field using conidia suspensions in order to fulfill Koch's postulates. Presence of characteristic rounded spots and pycnidia was evaluated on the inoculated leaves 9 and 23 days after inoculation. This study represents the first update on S. pistaciarum in Italy since its first identification in 1934.

Further Investigation on Limb Dieback of Fig (Ficus carica) Caused by Neoscytalidium dimidiatum in California

Fig limb dieback is a cosmopolitan disease caused by Neoscytalidium dimidiatum (Botryosphaeriaceae), characterized by branch and shoot cankers, discoloration of woody tissues, and dieback. The present study investigated the etiology of the disease in California that seems to have become prevalent among fig orchards in the last several years. During orchard surveys in Fresno, Kern, and Madera Counties over 3 years, we isolated consistently and evaluated the pathogenicity of N. dimidiatum under laboratory and field conditions. The effect of summer and winter pruning on the disease severity and the effects of different environmental and mechanical stresses, such as sunburn and wounding by mallets, were assayed. In addition, the susceptibility of six different cultivars and the effects of eradicating cankered shoots from the fig trees as a method to combat the spread of the disease were studied. Pathogenicity tests demonstrated that N. dimidiatum induces cankers on fig, mainly on wounded shoots. Results from the remaining experiments revealed that summer infection leads to more severe canker lesions than those induced by winter infection and that stressed shoots are more susceptible to infection than nonstressed shoots. 'Brown Turkey', 'Conadria', and 'Calimyrna' cultivars (all nonpersistent figs, i.e., needing pollination for fruit development) were less susceptible than the more susceptible 'Kadota', 'Sierra', and 'Black Mission' (all persistent figs, i.e., not needing pollination for fruit development). Canker removal from the orchard seems to be a good agronomic practice to avoid the spread of disease.