In the last decade, several studies demonstrated that plants have developed a tight partnership with the edaphic microbial communities, mainly bacteria, fungi, and archaea. Such microbiome accomplishes essential functions and ecological services complementary to the functions encoded by the host plant, conferring adaptive advantages to the plant, particularly during stressful conditions. The interaction between microbial communities and their host plants in the natural ecosystem are complex and the mechanisms regulating these mutualistic associations are not fully elucidated. Several biotic and abiotic factors have been shown to be important during this process, including the plant properties (species, age, stage, etc.), the soil type and agronomic practices, the geo-climate conditions, and the biotic interaction. In this context, the vineyard ecosystems represent a unique biogeography model to study and disentangle microbial biodiversity patterns (compositional diversity and potential functionality) across plants cultivated in different geographical regions. Here, I used the rhizosphere and bulk soil of seven different rootstock-scion combinations (Vitis spp.) to dissect the main factors driving the microbial communities’ recruitment in ten different vineyards in Tuscany (Italy), distributed in the Pomino and Nipozzano estates of Frescobaldi company. Among the factors investigated, I focused my attention on the geographical area, soil type and rootstock-scion combination. By using high-throughput sequencing of bacterial 16S rRNA gene and fungal ITS region, I show how both bacterial and fungal communities associated with grapevine rhizosphere and bulk soils are mainly affected by the geographical area and the soil. Nonetheless, I also revealed that the rootstock-scion combination is an important driver in shaping the microbial community, explaining a higher percentage of variability in comparison with the factors rootstock and scion taken alone. Overall, the results obtained in my thesis offer a new perspective of research that aim to develop a deep understanding about the contribution of scionrootstock combinations in the microbial community ecology of the plant holobiont. Keywords: Plant-microbe interactions, edaphic microorganisms, Microbial ecology, Plant Growth Promoting Bacteria, Rootstock-scion, Grapevine.

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MSc (Horticulture) / Department of Horticultural Sciences / Grafting is the process of combining two parts of plants to form a single plant. Grafting is a common technique in trees and vine crops and is becoming popular in annual vegetable production in order to control biotic and abiotic stresses, improve fruit yield and quality. The objectives of the study were to determine the (a) compatibility of the tomato scion x rootstocks combinations (b) effect of rootstocks on vegetative growth parameters (c) effect of tomato rootstocks on fruit quality and yield of tomato. The experiments were conducted under a protected environment (in a high tunnel) at the University of Venda, Thohoyandou, South Africa. Four tomato rootstocks (‘Powapak’, ‘Everest’, ‘Matterhorn’ and ‘Golf’) and two scion cultivars (‘Money Maker’ and ‘Rodade’) were used to develop 10 scion x rootstock combinations. The tube grafting method was used. Seedlings were transplanted in the polyethylene bags inside the high tunnel. Growth parameters, including plant height, stem diameter, number of leaves per cluster as well as yield attributes were measured. In addition, the chemical fruit quality parameters including the total soluble solids and pH were determined. A randomized complete block design with four replications was used for the study. Quantitative data sets of the variables were subjected to analysis of variance. There was a high plant survival rate and the number of clusters per plant showed marked improvement in some grafting combinations particularly in ‘Rodade x Everest’ and ‘Money Maker x Everest’. A few individual stunted plants were observed in the tunnel. A significant seasonal effect was observed on some of the growth and productivity attributes. The pH showed a narrow range of values and there was significant interaction between sampling time and genotype. The results demonstrated the viability of producing grafted tomatoes under tunnel conditions. / NRF

Three orange cultivar trials have been established in Arizona, one at the Yuma Mesa Agricultural Center, Yuma, AZ and one at the Citrus Agriculture Center, Waddell, AZ. For the navel orange trial in Yuma, ‘Fisher’ navel continues to have the greatest yield, but is unacceptably granulated For the Waddell trial, the second year data has been collected, and suggests that ‘Fisher’ and ‘Beck- Earli’ are outperforming the other cultivars tested to date.

Three lemon cultivar selection trials are being conducted at the Yuma Mesa Agriculture Center in Somerton, AZ. Data from these trials suggest that ‘Limonero Fino 49’ selections may be a suitable alternative for the varieties most commonly planted in Southwest Arizona today. ‘Cavers Lisbon’ and ‘Villafranca’ might also be planted on an experimental basis

Four 'Lisbon' lemon selections, 'Frost Nucellar', 'Corona Foothills', 'Limoneira 8A' and 'Prior' were selected for evaluation on Citrus volkameriana rootstock. 1994-2002 results indicate that the 'Limoneira 8A Lisbon' and ‘Corona Foothills Lisbon’ are superior in yield and fruit size. Results for 2002-03 indicate that these cultivars as well as ‘Frost Nucellar’ have superior yield.

In a rootstock evaluation trial planted in 1993, five rootstocks, ‘Carrizo’ citrange, Citrus macrophylla, ‘Rough Lemon’, Swingle citrumelo and Citrus volkameriana were selected for evaluation using 'Limoneira 8A Lisbon' as the scion. 1994-2002 yield and packout results indicate that trees on C. macrophylla, C. volkameriana and ‘Rough Lemon’ are superior to those on other rootstocks in both growth and yield. C. macrophylla is outperforming C. volkameriana. For the second year in a row, ‘Rough Lemon’ trees performed similarly to C. macrophylla and better than C. volkameriana. ‘Swingle’ and Carrizo’ are performing poorly. In two other rootstock evaluation trials, both planted in 1995, C. macrophylla and/or C. volkameriana are outperforming other trifoliate and trifoliate-hybrid rootstocks under test.

Four 'Lisbon' lemon selections, 'Frost Nucellar', 'Corona Foothills', 'Limoneira 8A' and 'Prior' were selected for evaluation on Citrus volkameriana rootstock. 2004-05 results indicate that the 'Limoneira 8A Lisbon' and ‘Corona Foothills Lisbon’

Two orange cultivar trials have been established in Arizona, one at the Yuma Mesa Agricultural Center, Yuma, AZ and one at the Citrus Agriculture Center, Waddell, AZ. For the navel orange trial in Yuma, all the selections had improved yields in 2004-05. ‘Fisher’ navel continues to have the greatest yield, but is quite granulated. Of the rest in the Yuma trial, ‘Lane Late’ had the best quality and yield. For the Waddell trial, the fourth year data has been collected, and suggests that ‘Fisher’, ‘Beck-Earli’, ‘Chislett’ and ‘Lane Late’ are outperforming the other cultivars tested to date.

In a rootstock evaluation trial planted in 1993, five rootstocks, ‘Carrizo’ citrange, Citrus macrophylla, ‘Rough Lemon’, Swingle citrumelo and Citrus volkameriana were selected for evaluation using 'Limoneira 8A Lisbon' as the scion. 1994-2004 yield and packout results indicate that trees on C. macrophylla, C. volkameriana and ‘Rough Lemon’ are superior to those on other rootstocks in both growth and yield. C. macrophylla is outperforming C. volkameriana. For the second year in a row, ‘Rough Lemon’ trees performed similarly to C. macrophylla and better than C. volkameriana. ‘Swingle’ and Carrizo’ are performing poorly. In two other rootstock evaluation trials, both planted in 1995, C. macrophylla and/or C. volkameriana are outperforming other trifoliate and trifoliate-hybrid rootstocks under test.