Chiara Catalano

Ciclo: XXXV

Data inizio: 31/10/2019

Curriculum: Agroalimentari

Borsa: UniCT

Titolo tesi: Deciphering the genetic determinism of the tolerance to biotic stress in lemon combining genetic and histological approaches

Abstract: Lemon [Citrus limon (L.) Burm. f.] is an evergreen three crop belonging to the genus Citrus, family Rutaceae, and it is appreciated worldwide for the organoleptic and nutraceutical properties of both the juice and the peel of its fruits. Around the 48% of global lemon production takes place in the countries of the Mediterranean and Black Sea areas (Spain, Italy, Greece, Turkey, Egypt, Lebanon) even if in this basin its cultivation is strongly hampered by the endemic presence of the mitosporic fungus Plenodomus tracheiphilus (Petri) Gruyter, Aveskamp and Verkley (syn. Phoma tracheiphila (Petri) Kantschaveli and Gikashvili) which causes a severe tra-cheomycosis called mal secco. The pathogen penetrates plants through wounds and colonises xylem vessels causing vein chlorosis of young shoots leaves, followed by leaf fall, wood discoloration, necrosis, and the progressive desiccation of the whole plant. To date, no agronomic or chemical means have proven to be effective in containing the diffusion of the patho-gen, neither breeding programs reached the goals of deciphering the genetic mechanisms of resistance to the pathogen and of developing novel varieties coupling optimal fruit quality and tolerance to mal secco disease. A lemon segregating population (125 individuals) was developed by crossing the mal secco-tolerant lemon variety ‘Interdonato’ (female parent) with ‘Femminello Siracusano 2Kr’ lemon (male parent), which produces good quality fruits but is highly susceptible to mal secco and was employed for a marker-trait association study aimed at the identification of molecular markers linked to the resistance towards mal secco. The behaviour of the full-sib population towards mal secco infection has been monitored after artificial inoculation of the pathogen, through an approach including visual assessment of the symptoms. The presence of the pathogen in symptomatic tissues was then assessed by Real Time PCR amplification and in vitro isolation. In citrus reference genotypes, histological studies were also per-formed for investigating more in-depth resistance towards mal secco and revealed a correlation between xylem vessel density and susceptibility to the disease. Taking advantage from the recent de novo sequencing of lemon genome, the full-sib population was genotyped through the Single Primer Enrichment Technology (SPET) approach, and QTL analysis on selected SNPs led to the identification of genomic regions significantly associated with resistance to mal secco disease, where genes were in silico annotated and gene ontology analysis highlights their involvement in defence response to fungus attack and to wounding. Since the lemon segregating population was naturally attacked by the two-spotted spider mite (Tetranychus urticae Koch), a damaging phytophagous mite difficult to control, showing a wide range of symptoms among the different genotypes, the response of the plants to the phytophagous mite was also considered. To do so, bioassays were developed ad hoc using detached leaves placed in special experimental arenas and the QTL analysis was also performed. Among in silico annotated genes, two encoding for eugenol synthase, a well-known acaricide volatile compound, were identified. This proves that even though the full-sib population was constituted for a specific purpose, it could be also useful for studying many other agronomic traits of interest (e.g., resistance towards pathogens and pests, fruit quality, spinescence, polyembryony, etc.). Overall, phenotyping protocols were employed for large-scale susceptibility assessment for mal secco disease and for the two-spotted spider mite attack, and candidate genes associated with resistance to both biotic stresses were successfully identified. In the next future, the results of the present research will be implemented in Marker Assisted Selection (MAS) and in genome editing experiments, thus improving the cost- and time-effectiveness of lemon genetic improvement programs.

Tutor: prof.ssa Alessandra Gentile e prof. Gaetano Distefano

Data Conseguimento Titolo: 23/11/2022

Email: chiara.catalano@unict.it

Cellulare: 

Periodi all'estero- Sede e data: Tel Aviv University, Tel Aviv, Israele, novembre 2021 - marzo 2022

Esperienze post-Dottorato ed attuale occupazione: RTD-A presso Università degli Studi di Catania