Olivieri, Fabrizio (2020) Genetic and genomic approaches to improve tomato genotypes for tolerance to high temperature condition. [Tesi di dottorato]


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Item Type: Tesi di dottorato
Lingua: English
Title: Genetic and genomic approaches to improve tomato genotypes for tolerance to high temperature condition
Olivieri, Fabriziofabrizio.olivieri@unina.it
Date: 13 March 2020
Institution: Università degli Studi di Napoli Federico II
Department: Agraria
Dottorato: Scienze agrarie e agroalimentari
Ciclo di dottorato: 32
Coordinatore del Corso di dottorato:
d'Urso, Guidodurso@unina.it
Date: 13 March 2020
Uncontrolled Keywords: Heat-Tolerance Yield-related traits, High-throughput genotyping
Settori scientifico-disciplinari del MIUR: Area 07 - Scienze agrarie e veterinarie > AGR/07 - Genetica agraria
Date Deposited: 20 Mar 2020 15:37
Last Modified: 31 Oct 2021 21:34
URI: http://www.fedoa.unina.it/id/eprint/13236


Global warming and the growing food demand due to the world population growth are two critical threats affecting food availability in the next future. The predicted dangerous scenario is the raise of temperatures that could lead to increases between 1.8 and 4.0 °C higher than present in the year 2100. In crop plants, the high temperature (HT) can affect all the reproductive stages starting from pollen viability to final crop yield. Tomato (S. lycopersicum) is an important crop distributed worldwide. Notwithstanding its South American origin, the raising of temperatures up to 35°C during the reproductive phases could negatively affect the number of flowers, the fruit set and, consequently, the final yield. For this reason, the selection of tolerant genotypes is one of the main efforts to face tomato yield reduction under the increasing temperatures. A group of tomato genotypes was evaluated for five yield-related traits under high temperature conditions, such as the number of flowers per inflorescence (NFL), fruit set (FS), number of fruit per plant (TNF), fruit weight (FW) and yield per plant (YP) collecting data in three experimental trials located in Campania and Puglia in two years. The statistical analysis revealed that for all traits the genotype by environment interaction resulted statistically significant. Moreover, correlation analyses evidenced that TNF resulted the major yield component in the trials, contributing positively to the final YP. A selection index (SI) was also calculated considering all traits showing a positive correlation to YP and it allowed to select seven genotypes and two hybrid controls as the best performing in three different environments. A stability analysis revealed that one genotype (E42) showed high- and stable-yield trait and a YP comparable to those of two F1 hybrids selected for high yield under HT. In order to investigate the genetic variability of the assayed genotypes in the present thesis, two different approaches were used to identify Candidate Genes (CGs) and QTLs putatively involved in the response to HT. The first consisted of a GWAS analysis carried out on a larger population using a high-throughput genomic platform that allowed the identification of 14 marker-associations to the yield-related traits. In particular, 11 genes and a QTL associated to YP were identified that could be involved in the tolerance response. The second approach was the use of a genotyping-by-sequencing (GBS) technique performed on 21 genotypes in order to study the genetic variability that could be used for identification of CGs putatively involved in the tolerance to HT and applied in breeding strategies. A SNP effect analysis was performed to predict how SNPs/InDels could affect the protein effectiveness. Fifty-three SNPs and 55 InDels showed a disruptive effect on protein functions. In the evaluation of the whole genome variability, two genotypes (E36 and E48) showed a very low number of private SNPs/InDels (78 and 97, respectively), whereas the genotypes E42 (9,146 SNPs/InDels) and PDVIT (9,421 SNPs/InDels) showed the highest percentage of private mutations. The high genetic variability recorded in these two genotypes was explored by BLAST analysis carried out on 82 markers, evidencing the presence of wild introgressed regions in both genotypes. Moreover, the calculation of Identity-by-State (IBS) analysis was performed in order to calculate the genetic distances among all genotypes. The analysis confirmed that E42 and PDVIT were genetically different from the other genotypes, with IBS values ranging from 0.60 and 0.71. Combining the genotypic information with YP and quality traits recorded in previous studies, 19 F1 hybrid combinations were obtained. In 2018, the hybrids were evaluated for three yield-related traits (TNF, FW and YP) and four hybrids were selected for their high percentages of heterosis (%Het) for YP: 17H14 (%Het=45.45), 17H36 (%Het=25.63), 17H37 (%Het=498.64) and 17H39 (%Het=25.96). These four hybrids were evaluated for a second year, also recording two qualitative traits (Total Soluble Solid Content, TSSC and Titratable Acidity, TA). The hybrids 17H37 and 17H39 confirmed their high percentage of heterosis for both yield and fruit quality traits. Finally, a genome editing approach was used to investigate the role of two HSPs in the tolerance to high temperatures. Genetic transformation of a heat tolerant introgressed line (IL4-4) was performed starting from the study of gene expression analysis of two HSP90 acting during the reproductive stages. The analysis revealed that the heat tolerant genotype IL4-4 showed a significant increase of gene expression in these two genes in ovary tissues, with peaks between the 4th and the 7th day post-anthesis, suggesting that these genes might play a key-role in the embryo development. In this way, up till now, 7 transformant plants have been obtained and are under evaluation. Comprehensively, the present study showed that the combination of a rigorous phenotyping activity carried out in multi-environmental conditions with the acquisition of genotypic data represents a successful choice to enhance innovative breeding programs for the selection of genotypes and hybrids under harsh temperature conditions.


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