La mela è uno dei frutti più importanti prodotti a livello mondiale. La coltivazione è compromessa da numerose malattie e alterazioni fisiologiche, che portano a importanti perdite a livello economico. Un'alterazione emergente riscontrata negli ultimi anni nelle zone di produzione è la patina bianca, che si manifesta come un sottile strato biancastro formato da ife e spore fungine, aderente alla superficie dei frutti. La patina bianca è stata inizialmente descritta come un'alterazione post-raccolta, ma in seguito è stato osservato che i sintomi possono essere riscontrati anche prima o durante il periodo della raccolta. I fattori che sembrano favorirne la comparsa sono l'alta umidità relativa, le basse temperature e alcune pratiche agronomiche come l'uso di reti antigrandine e la concimazione fogliare. Gli agenti causali sono stati inizialmente identificati come specie appartenenti al genere Tilletiopsis. Il genere è stato recentemente revisionato e la maggior parte delle specie è stata riclassificata in generi differenti. Queste specie fungine sono presenti in vari ambienti, ma sono principalmente considerate comuni abitanti del filloplano. Diverse specie simil-Tilletiopsis sono state associate alla patina banca in alcune aree europee dove l'alterazione è stata riportata: nei Paesi Bassi, nel Sud Tirolo e altre regioni del Nord Italia, in Germania e in Croazia. L'obiettivo di questo lavoro è stato quello di indagare la presenza e la diversità delle specie simil-Tilletiopsis associate alla patina bianca in Piemonte. I ceppi fungini sono stati isolati da frutti sintomatici, provenienti da frutteti e da magazzini di conservazione, e da frutticini, foglie e corteccia raccolti in frutteto. Il DNA è stato estratto dai ceppi isolati ed è stata amplificata la regione ITS. Sulla base dei risultati preliminari ottenuti, sono stati selezionati alcuni ceppi rappresentativi per i quali è stato amplificato il dominio D1/D2 del gene dell'LSU rRNA. In seguito è stata effettuata l'analisi filogenetica. Tra gli isolati identificati tramite filogenesi, è stato selezionato un ceppo rappresentativo per ogni specie al fine di verificare la capacità di riprodurre i sintomi su mele artificialmente inoculate mantenute a 15°C e a 25°C. In totale sono stati isolati 65 ceppi fungini, appartenenti a quattro specie: Entyloma belangeri, Golubevia pallescens, Golubevia sp. 1 e Tilletiopsis washingtonensis. La principale specie riscontrata in termini di isolati sequenziati è stata G. pallescens, seguita da T. washingtonensis. Un ceppo è stato identificato come E. belangeri. Tre ceppi possedevano sequenze diverse da quelle delle specie note e formavano un gruppo distinto all'interno dell'ordine Golubeviales. Sono stati considerati come una possibile nuova specie, provvisoriamente chiamata Golubevia sp. 1. Tutti gli isolati hanno mostrato capacità di riprodurre i sintomi della patina bianca sulle mele artificialmente inoculate e mantenute a 15°C, con incidenza variabile a seconda del ceppo. Nessun isolato è stato capace di riprodurre i sintomi sui frutti a 25°C, confermando che le basse temperature contribuiscono alla comparsa di questa alterazione. Questo studio ha permesso di ottenere nuove informazioni riguardo la diversità di specie associate alla patina bianca in Piemonte. Dal momento che pochi studi sono stati condotti sulla patina bianca e poche informazioni sono disponibili, i risultati forniscono dati utili al fine di aumentarne le conoscenze.
Apple is one of the most important fruit crops in the world. The cultivation is affected by many diseases and disorders, leading to important economic losses. An emerging issue found in recent years in apple producing areas is white haze. This disorder manifests as a thin layer of fungal growth whitish to pale grey in colour, adhering to the apple skin. It was first described as a post-harvest disorder, but subsequent surveys showed that symptoms can appear also before or during harvesting. Factors that can promote the appearance of symptoms seems to be a high relative humidity, low temperatures and novel practices such as the use of hail-protection nets and foliar fertilization. The causal agents were first identified as several species belonging to the genus Tilletiopsis. The genus was recently emended, as it was demonstrated that it was polyphyletic, and most of the species were transferred into different genera. These fungal species are present in various environment, but they are mainly considered common inhabitants of the phylloplane. Several Tilletiopsis-like fungi were associated with white haze of apple in European areas where the disorder was reported and studied: the Netherlands, Sud Tyrol and other regions of Northern Italy, Germany and Croatia. In recent years the presence and the development of white haze were observed in Piedmont. The aim of this work was to explore the presence and the diversity of Tilletiopsis-like fungi associated with white haze in this area. The fungal strains were isolated from symptomatic fruits, coming from orchards and from cold storage, and from asymptomatic fruits, leaves and wood collected in the orchards. DNA was extracted from isolated strains and the ITS region was amplified. Basing on preliminary results obtained, representative strains were selected for amplification of D1/D2 domains of LSU rRNA gene. The ability of isolated fungal species to reproduce symptoms of white haze was assessed. Strains representative of the species identified through phylogeny were selected and were artificially inoculated on apples, placed at 15°C and 25°C. A total of 65 Tilletiopsis-like fungi were isolated. The strains were identified as belonging to four species spread across the class Exobasidiomycetes: Entyloma belangeri, Golubevia pallescens, Tilletiopsis washingtonensis and a putative new species, Golubevia sp. 1. The most abundant in term of sequenced isolates was G. pallescens, followed by T. washingtonensis. One strain was identified as E. belangeri. Three strains showed sequences that differed from those of any recognized species, and the phylogenetic analysis showed that they formed a distinct clade into the order Golubeviales. Consequently, they were considered a potential new species, named Golubevia sp.1. All the fungal strains were able to reproduce symptoms of white haze on apples artificially inoculated placed at 15°C, with variable incidence depending on the inoculated strain. None of the species was able to reproduce symptoms on fruits placed at 25°C, confirming that lower temperatures contribute to the appearance of the disorder. The present study allowed to obtain new information about species diversity associated with white haze. As only few studies were conducted and little is known about white haze, results coming from this work provides useful data that will lead to an increasing understanding of the disorder.
Diversità e caratterizzazione di specie fungine simil-Tilletiopsis responsabili della patina bianca, una nuova minaccia per la produzione di mela.
REMOLIF, GIULIA MARIA ELENA
2018/2019
Abstract
Apple is one of the most important fruit crops in the world. The cultivation is affected by many diseases and disorders, leading to important economic losses. An emerging issue found in recent years in apple producing areas is white haze. This disorder manifests as a thin layer of fungal growth whitish to pale grey in colour, adhering to the apple skin. It was first described as a post-harvest disorder, but subsequent surveys showed that symptoms can appear also before or during harvesting. Factors that can promote the appearance of symptoms seems to be a high relative humidity, low temperatures and novel practices such as the use of hail-protection nets and foliar fertilization. The causal agents were first identified as several species belonging to the genus Tilletiopsis. The genus was recently emended, as it was demonstrated that it was polyphyletic, and most of the species were transferred into different genera. These fungal species are present in various environment, but they are mainly considered common inhabitants of the phylloplane. Several Tilletiopsis-like fungi were associated with white haze of apple in European areas where the disorder was reported and studied: the Netherlands, Sud Tyrol and other regions of Northern Italy, Germany and Croatia. In recent years the presence and the development of white haze were observed in Piedmont. The aim of this work was to explore the presence and the diversity of Tilletiopsis-like fungi associated with white haze in this area. The fungal strains were isolated from symptomatic fruits, coming from orchards and from cold storage, and from asymptomatic fruits, leaves and wood collected in the orchards. DNA was extracted from isolated strains and the ITS region was amplified. Basing on preliminary results obtained, representative strains were selected for amplification of D1/D2 domains of LSU rRNA gene. The ability of isolated fungal species to reproduce symptoms of white haze was assessed. Strains representative of the species identified through phylogeny were selected and were artificially inoculated on apples, placed at 15°C and 25°C. A total of 65 Tilletiopsis-like fungi were isolated. The strains were identified as belonging to four species spread across the class Exobasidiomycetes: Entyloma belangeri, Golubevia pallescens, Tilletiopsis washingtonensis and a putative new species, Golubevia sp. 1. The most abundant in term of sequenced isolates was G. pallescens, followed by T. washingtonensis. One strain was identified as E. belangeri. Three strains showed sequences that differed from those of any recognized species, and the phylogenetic analysis showed that they formed a distinct clade into the order Golubeviales. Consequently, they were considered a potential new species, named Golubevia sp.1. All the fungal strains were able to reproduce symptoms of white haze on apples artificially inoculated placed at 15°C, with variable incidence depending on the inoculated strain. None of the species was able to reproduce symptoms on fruits placed at 25°C, confirming that lower temperatures contribute to the appearance of the disorder. The present study allowed to obtain new information about species diversity associated with white haze. As only few studies were conducted and little is known about white haze, results coming from this work provides useful data that will lead to an increasing understanding of the disorder.| File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.14240/49246