Pomodoro M82 vs Solanum pennellii: l'impatto dello stress idrico e della micorrizazione in una linea commerciale di pomodoro vs un parente selvatico

This thesis work has been developed in the framework of the European TOMRES project, whose purpose is to enhance resilience to combined water and nutrient stress in tomato, as a model crop, in prevision of an increase in frequency and severity of drought events due to global climate change. The final aim is to reduce the environmental impact of agricultural activities. The domesticated tomato, Solanum lycopersicum, is an economically relevant crop species as well as a useful model organism in the study of plant-microbe interaction since it responds to mycorrhizal colonization and native microbiota. In nature, arbuscular mycorrhizal (AM) symbiosis is the most ancient and widespread mutualistic association between soil fungi and the roots of land plants. AM fungi, in exchange of organic carbon provided by the plant host, enhance the plant uptake of water and mineral nutrients, mainly phosphate (P), with the effect of increasing plant biomass. The purpose of my thesis is to evaluate the response to mycorrhization (using the AM fungus Funneliformis mosseae) of two tomato wild relatives tolerant to drought, i.e. Solanum pennellii (SPE) and Solanum neorickii (SNEO), versus the cultivated tomato Solanum lycopersicum cv "M82" (SLY). The plants were grown in a miniature industrial culture system (alveolar trays) under combined water and nutrient stress (SS) condition, according to TOMRES guidelines. The first part of the work has been devoted to screen the two wild relative species based on several plant responses, i.e. plant nutritional status through the SPAD index, mycorrhiza growth response (MGR) index and AM colonization of the roots. Solanum pennellii was the most interesting since resulted to be weakly susceptible to the AM symbiosis. It was therefore chosen for a new set of experiments. The responses of S. pennellii versus tomato M82 to the AM fungus were evaluated again to validate the first experimental set; in addition, some molecular approaches were used to describe gene expression in mycorrhizal tomatoes under combined stress conditions. Moderate water stress was induced in plants by 40% soil water capacity (SWC40%), while the nutrient stress was performed by using a fertilizer solution with 3.2 μM and 50 μM P concentration in the first and second set of experiments, respectively. RESULTS: a) the wild tomatoes, having a greater genetic diversity than the cultivated tomato (who have undergone a domestication bottleneck), are hypothesized to be more resistance to stress; however, growing in alveolar trays, their biomass was negatively affected by nutrient stress (P 3.2 or 50 μM); b) mycorrhization had a general neutral or negative effect on biomass of the wild tomatoes, but the nutritional status of S. pennellii was improved under nutrient stress (P 3.2 μM) and normal watering (WW) condition; c) surprisingly, a wild species living in natural environments (S. pennellii) presented a lower level of AM colonization than the crop variety of tomato selected and adapted to high agricultural fertilization according to the ¿green revolution¿; d) even when the level of mycorrhizal colonization is low, like in S. pennellii, the AM symbiosis is functioning, as demonstrated by the correct expression of two marker genes (PT4 and FatM) in RT-PCR analysis; as resulting from the preliminary data of RNA-Seq, S. pennellii reveals a general responsiveness at transcriptional level (and a positive response at hormonal-regulation level) to the AM symbiosis