Digital Theses Archive


Tesi etd-04132023-181557

Type of thesis
Application of arbuscular mycorrhizal fungi in sustainable agriculture
Scientific disciplinary sector
Istituto di Scienze della Vita - PHD IN AGROBIOSCIENZE
relatore ERCOLI, LAURA
  • arbuscular mycorrhizal fungi
  • biofertilization
  • community diversity
  • crop yield
  • food quality
  • functional groups
  • nutrients
Exam session start date
• The whole research aimed to test the general hypothesis that arbuscular mycorrhizal fungal (AMF) inoculation in the field positively affected yield, nutrient uptake and the synthesis of primary and secondary metabolites, and that AM fungal colonization and AM diversity in roots are playing key roles in the output of the symbiosis. To this aim, two multi-year field experiments of AMF inoculation were carried out on tomato (Solanum lycopersicum L.) and sunflower (Helianthus annuus L.).<br>• Starting from the fact that AMF species belonging to Gigasporaceae and Glomeraceae families vary in life-history strategies we hypothesed that this trait may determine differential effects on tomato fruit yield and quality, nutrient uptake, and residue decomposition. We also hypothesized that since the development of the inoculated AMF species within the roots can be affected by life-history strategies which interact with the parameter “competition with native AM fungal community”, the differences at family level would affect not only AMF root colonization, but also AMF diversity in roots. Then, we dissected the roles of this two traits in determing tomato fruit quality. To this aims, we field inoculated two tomato varieties with four AMF species belonging to Glomeraceae and Gigasporaceae, and fungal colonization, yield, fruit nutrient concentration, litter decomposition, bacterial and fungal abundances in soil, AM fungal diversity in roots were assessed. <br>• Overall Gigasporaceae promoted the concentration of nutrients in tomato fruits compared to Glomeraceae. A variability in AM fungal colonization and fruit nutrient concentration was detected within Glomeraceae. Within Gigaspoarceae, Scutellospora pellucida increased the yield (+27%) of var. Rio Grande with respect to Gigaspora gigantea. In var. Rio Grande, inoculation with Funneliformis mosseae (Glomeraceae) did not change litter decomposition as compared to non-inoculated controls, whereas it was lower than in Sclerocystis sinuosa (Glomeraceae) and Gigasporaceae species, which showed the highest decomposition rates. AMF inoculation promoted soil total bacterial and fungal abundance and fungal:bacterial (F:B) ratio compared to controls, and members of Gigasporaceae had the highest F:B ratio. Moreover AM fungal colonization increased total phenolic content (TPC) in fruits of both varieties at 1st and 2nd harvests, antioxidant activity (ORAC) at 1st and 2nd harvests in var. Rio Grande and lycopene at 2nd harvests in both varieties. In var. Rio Grande, members of Gigasporaceae increased TPC at 1st harvest and ORAC at both harvests in comparison with members of Glomeraceae. In var. Pisanello fruits of plants inoculated with G. gigaspora had higher values of TPC at both harvests, of ORAC at 1st harvest and of lycopene at 2nd harvest as compared to fruits of plants inoculated with S. pellucida.<br>• Using the small subunit-internal transcribed spacer-large subunit (SSU-ITS-LSU) rDNA sequence, foreign-inoculated strains of G. gigantea, S. pellucida, F. mosseae and S. sinuosa were retrieved at 2nd harvest within the roots of tomato var. Pisanello as well as at transplanting and 2nd harvest within the roots of tomato var. Rio Grande. In var. Pisanello, at 2nd harvest, the phylogenetic maximum likelihood (ML) tree allowed to discriminate a total of 11 AM fungal phylotypes. In var. Rio Grande, at transplanting, we successfully verify the unique presence in the roots of the AM fungal inoculants, whereas at 2nd harvest, we found a total of 15 AM fungal phylotypes. In both tomato varieties, a functional relationship between AM fungal root colonization and fruit quality was found and DistLM analysis supported the main role played by arbuscules in determining the quality pattern. Non-metric multidimensional (nMDS) plots, representing the AM fungal community structure within the roots of both tomato varieties, showed that all treatments were well separated among each other. In addition, the RELATE analysis supported, only in var. Rio Grande, a significant relationship between AM fungal community structure in root and quality parameters, and DistLM analysis allowed to highlight the main role played by Archeospora sp., Rhizophagus fasciculatus and Rhizophagus sp. in determining the fruit quality pattern.<br>• In the two-year field study with sunflower, we inoculated a locally sourced and highly infective consortium consisting of AM fungi originating from a local field site. In this second experiment, we aimed to elucidate the effect of the potential increase of AM fungal abundance and changes of mycorrhizal community structure following field inoculation in two contrasting soil conditions, i.e., high and low soil fertility. The mycorrhizal benefit of this oil crop, putatively highly responsive to AM fungal inoculation, was evaluated by plant growth, nutrient uptake, seed and oil yield and quality, while the abundance and community structure of AMF were measured by the assessment of AM fungal root colonization and relative abundances of taxa within the root AM fungal community. We hypothesized that both functional fungal traits (i.e, AM fungal abundance and community structure) would have been highly modified under low soil fertile conditions, with subsequent multiple beneficial effects for the host.<br>• In both years of cultivation (2019 and 2020), at R5.5 growth stage (beginning of flowering) AM fungal inoculation increased the percentage of root length containing vesicles and AM fungal root colonization. Using the small subunit ribosomal RNA (SSU) rDNA sequence, a total of 22 and 15 AM fungal Virtual Taxa (VT) were retrieved in 2019 and 2020, respectively, in roots of AM fungal inoculated and mock inoculated sunflower. The PERMANOVA showed that the AM fungal community structure within the roots of sunflower in both years of cultivation was significantly affected by AM fungal inoculation. <br>• In 2019, AM fungal inoculation improved root and shoot dry weight at R5.5 growth stage and head diameter, root system radius and tap root length of sunflower plants at full maturity. In 2020, at full maturity, plant height and tap root length were promoted by AM fungal inoculation. Moreover, in 2019 and in 2020 AM fungal inoculation improved oil yield by 36% and 20%, respectively, and grain yield by 16% in 2020. In both years of cultivation AM fungal inoculation increased the content of all the macro- and micronutrients in grain (N, P, K, Ca, Mg, Fe, Zn, Cu and Mn), with the exception of Zn in 2020. In 2019, AM fungal inoculation significantly affected all analyzed fatty acids (FA) in the oil, with the exception of eicosanoic acid (C20:1). In addition, non-metric multidimensional scaling (NMDS) analysis showed that fatty acid composition of oil samples of inoculated plants was significantly different from the control. In 2020, SIMPROF clustering showed that volatile organic compound (VOC) profiles of inoculated and not-inoculated samples grouped separately and PERMANOVA confirmed the observed differences in VOC profiles.<br>• This work highlights the importance of applying AM fungal inocula to tomato at nursery for improving yield, fruit nutrient concentrations and quality parameters. Nursery inoculation of vegetables is easy to perform and may generate time and cost benefits compared to soil inoculation. Morover, AM fungal species inoculated at nursery could be detected at harvest within the roots of tomatoes and differentially modified AM fungal colonization traits and root community structures that were significatly correlected with positive benefits on fruit quality. The understanding of the plant responses to AM fungal functional traits turned out to be crucial for more efficient exploitation of AMF in sustainable agricultural biofertilizer programs targeted to the production of high-quality food. Overall Gigasporaceae, which accelerates litter decomposition, might be of great relevance for the uptake and translocation of several macro- and micro-nutrients and for the synthesis of health-promoting compound in tomato fruits and should be included in mixed microbial inoculants for the enhancement of the nutritional value of tomato under organic farming systems. Moreover, due to the variability of environmental conditions in time and space, host benefit could be greater with the application of communities having AMF with diverse life-history stategies. Therefore, we suggest that field inoculation with mixtures of members of Gigasporaceae and Glomeraceae families should be further studied to improve our knowledge on the significance of AM fungal functional groups for host nutrient response.<br>• Moreover, this work shows that the use of AM fungal local inocula may be very effective in improving sunflower grain and oil yield as well as seed quality. Multivariate analyses highligheted that local AM fungal inoculum, affecting AM fungal colonization traits and community structure, but not fungal composition, is more effective compared with mock-inoculated controls, expecially in low fertility conditions. Therefore, the use of local AMF consortia, produced on farm with mycotrophic plants species, might represent a convenient alternative to commercial AM fungal inocula, and offer economically and ecologically important advantages in sustainable cropping systems.<br>