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

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.

Potential Role of Biocontrol Agents for Sustainable Management of Fungal Pathogens Causing Canker and Fruit Rot of Pistachio in Italy

Pistachio (Pistacia vera) is an important Mediterranean crop. In Italy, pistachio is cultivated in the southern regions, of which Sicily is the main production area. Recently, the phytopathological situation of this crop has started to be updated, and new diseases have been discovered, studied, and reported. Botryosphaeriaceae spp. and Leptosillia pistaciae are major canker/rot pathogens, and Cytospora pistaciae and Eutypa lata have been reported as minor canker pathogens. In this paper, we evaluated different biological control agents, belonging to Trichoderma asperellum, T. atroviride and T. harzianum, as well as some Bacillus amyloliquefaciens strains, against above-mentioned pathogens. Results of dual culture assays showed that all the biological products, both fungi and bacteria, were able to inhibit the mycelial growth of the pathogens in vitro. Experiments using detached twigs showed no effect of biocontrol agents in reducing infections, except for Neofusicoccum hellenicum treated with T. harzianum T22 and Leptosillia pistaciae treated with B. amyloliquefaciens D747. Results of detached fruit experiments showed an efficacy ranging from 32.5 to 66.9% of all the biological products in reducing the lesions caused by N. mediterraneum. This study provides basic information for future research on biological control of pistachio diseases and future prospects for search of more effective biological control agents for canker diseases than those studied here.

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.