BIOTECHNOLOGICAL TOOLS TO STUDY TOMATO FRUIT QUALITY UNDER STRESS CONDITIONS
Creators: name: De Stefano, Rosalba
Publisher: name: Università degli Studi di Napoli Federico II
Year: 2013

description: The studies carried out during my Ph.D thesis focused on the identification of genetic mechanisms which regulate tomato fruit quality traits under abiotic (water deficit) and
biotic (Botrytis cinerea) stress conditions. Specifically the work was developed through two lines of research with certain objectives:
1) Identification of candidate genes controlling tomato fruit quality in response to water deficit, through microarray tools and the use of an Introgression line
(IL9-2-5).
2) The study of shelf life and Botrytis cinerea resistance of transgenic tomatoes enriched in flavonoid.
In the first part of study the selected approach consisted to study the peculiar behavior of the genotype IL9-2-5, an introgression line of the cultivated Solanum lycopersicum with a 9 cM introgression from the wild species Solanum pennellii. This introgressed segment gives fruits with high soluble solids amount and previous experiments, performed in laboratory where I worked, highlighted its superior
performances under water stress. This was confirmed in the present thesis. In particular, the Blum index (parameter that allows to evaluate yield of a cultivated plant under drought stress) evidenced a lower yield losses under 50% water treatment in IL9-2-5 compared with M82, in both two tolerance tests. In addition, phenotipic data for fruit quality highlighted very low changes in firmness, soluble
solids and nutrient content underlining more stability under water deficit in IL9-2-5 compared with M82, in the first tolerance test. Among phenotypic data, a stability in AsA content in IL9-2-5 under 50% water treatment was noteworthy, while in M82 was evident its dramatic decrease. Also transcriptomic data were in line with the hypothesis of a more stability of the IL9-2-5, specifically its comparison between the two water treatments in microarray analysis highlighted the low fold changes of transcripts, indeed only 5 probes differentially expressed were retrieved. On the
contrary, the elevated amount of TCs showing differential expression in M82 under 50% water treatment (204) indicated an activation/repression of a lots of genes involved in defense mechanisms towards abiotic stress. The correlation data (by CoExpression Tool) made possible to establish a relation among AsA metabolism, carbohydrate metabolism and water stress. This part of work allowed to identify IL9-
2-5 as a genotype to use in breeding programs to obtain fruit with good quality traits (in particular soluble solids and vitamin C amount, both important for tomato processing industry) reducing water consumption.
In the second part of study, transgenic tomatoes, accumulating different flavonoid compounds, were tested to have extended shelf life and enhanced pathogen
resistance to Botrytis cinerea. Comprehensively all the transgenic lines investigated were very interesting as healthy foods, but only purple and indigo tomatoes (both
accumulating anthocyanins) showed 2-fold longer shelf life and increased resistance to the opportunistic pathogen tested, compared with red tomato. On the other hand,
orange tomato (which accumulates flavonols) had longer shelf life compared with red tomato but shorter than purple and indigo tomatoes. In addition, orange tomato showed no resistance to Botrytis cinerea. Our data suggest that high antioxidant capacity of anthocyanins reduces the increase in reactive oxygen species, better than flavonols during late ripening stages, and scavenges H2O2 (and probably other
ROS too), produced by Botrytis c. during infection, better than flavonols, stopped necrosis damns. This part of work allowed to identify all transgenic lines investigated,
not only interesting as healthy foods, but also interesting to enhance fruit shelf life, but just purple and indigo to enhance also resistance to Botritys cinerea.