Banca de DEFESA: Tiago Silva Jorge

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : Tiago Silva Jorge
DATE: 30/08/2023
TIME: 14:00
LOCAL: Meio virtual
TITLE:

Groundnut ringspot orthotospovirus (GRSV) in lettuce and new hosts: Identification of susceptibility genes via transcriptomic analysis, search for new sources of natural resistance and mobilization of the Sw-5b resistance gene from tomato to lettuce via transgenics.

KEY WORDS:

GRSV, Lactuca sativa L., spotted wilt disease.

PAGES: 120
BIG AREA: Ciências Biológicas
AREA: Biologia Geral
SUMMARY:

Lettuce (Lactuca sativa L.) is one of the main leafy vegetables in Brazil and worldwide. Diseases caused by a complex of Orthotospovirus species (including groundnut ringspot orthotospovirus – GRSV and tomato spotted wilt orthotospovirus – TSWV) are among the most important of this vegetable. GRSV is the predominant viral species in Brazil and, up to now, lettuce cultivars with adequate levels of resistance are not available. This thesis was organized into five chapters. Chapters I & II present a review of this viral complex and the advances obtained through classical and biotechnological resistance breeding to orthotospoviruses in lettuce, Capsicum, and tomato crops. In Chapter III, experiments were conducted to identify new sources of genetic resistance to orthotospoviruses in germplasm of cultivated and wild lettuce species. Sixty-five (65) Lactuca accessions were initially evaluated under field (natural) inoculum conditions. Eleven (11) accessions (displaying low incidence/severity of symptoms) were selected for greenhouse trials via mechanical inoculation. Five different orthotospovirus isolates (three GRSV isolates and two TSWV isolates) were used. Three evaluated accessions (‘Bedford’, ‘Belíssimo’, and ‘UC12100’) showed low values of viral incidence (= high tolerance levels). No accessions showed immunity-like responses. This is the first study identifying sources of genetic tolerance to GRSV. In chapter IV, a transcriptomic analysis was conducted to identify genes differentially expressed across inoculated versus non-inoculated lettuce plants during the interaction between the susceptible cultivar ‘Salinas’ and a GRSV isolate. The total RNA of the plants was collected in five periods after inoculation (1 hour, 6 hours, 24 hours, 48 hours, and 7 days). The dynamics of viral replication over different times was determined via real-time PCR. The best time for transcriptomic analysis was identified at 48 hours after inoculation, when viral multiplication in the host tissues was initiated. The samples were then submitted to the RNA-seq. A total of 273 genes was found to be differentially expressed in the contrasts between inoculated versus non-inoculated plants, including different categories of gene functions. In chapter V, cisgenic lettuce events containing the tomato Sw-5b resistance gene were challenged under controlled inoculation conditions with a GRSV isolate. The evaluation of the effectiveness of the events was carried out by confirming the presence of the virus by visual and serological evaluation of diseased plants, with subsequent nucleic acid extraction and PCR with virus-specific primers. The genomic insertion of the Sw-5b gene and the presence of its transcripts were also evaluated in lettuce leaf tissues. Lettuce transformed with the Sw-5b gene showed high susceptibility to GRSV, with only a few asymptomatic plants. The Sw-5b gene product and its transcripts were detected in both symptomatic and asymptomatic plants, indicating that the transfer of this gene alone was not effective to provide resistance to GRSV in lettuce. In chapter VI, tests were conducted aiming at the characterization of new natural or experimental host species of GRSV among crops and weeds. Three crops have been reported as new natural hosts, including Cichorium endive, Cichorium intybus, and eggplant (Solanum melongena). Thirty accessions from the germplasm bank of jurubebas were challenged with a GRSV isolate to identify new potential experimental hosts. All accessions were susceptible. This result was confirmed by dot-ELISA test. Accessions of S. macrocarpon, S. acanthodes, S. viarum, S. subinerme, S. scuticum, S. stramoniifolium, and S. sisymbriifolium were reported as new experimental hosts of GRSV. This thesis provides new information that will help to establish more effective breeding and management strategies of diseases induced by orthotospoviruses in lettuce and other host crops.

COMMITTEE MEMBERS:
Externa à Instituição - Rosana Rodrigues - UENF
Presidente - ***.496.721-** - LEONARDO SILVA BOITEUX - EMBRAPA
Interna - 1723060 - RITA DE CASSIA PEREIRA CARVALHO
Interno - 2644635 - ROBERT NEIL GERARD MILLER
Externa à Instituição - SIMONE DA GRAÇA RIBEIRO - EMBRAPA