Background: Anthocyanin pigmentation characterizes a number of tissues of Citrus and its relatives. The gain and loss of pigmentation is intriguing and is inherited variously among species. Methods: Citrus germplasm was used to investigate the anthocyanin pigmentation of tissues never before considered, including stamen, style and stigma, and of young leaves, petals, rind and flesh of 28 genotypes belonging to 14 species. Citrus genotypes encompassed citron, lemon, sweet orange, lime, and Citrus relatives included Microcitrus, Murraya, and Severinia. A relative qRT-PCR analysis was carried out on the structural and regulatory genes: phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3′-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR), anthocyanidin synthase (ANS), uridine diphosphate glucose flavonoid glucosyl-transferase (UFGT), glutathione S-transferase (GST), Ruby and Noemi. Image analysis and a genomic approach were employed to evaluate how the red pigmentation is inherited among tissues and species. Results: Pigmentation of young leaves and petals is specific to citron and its hybrids. Ruby controls the pigmentation of petals, but not of leaves. The red color of the rind and flesh is a trait that particularly characterizes a diversity of sweet oranges, citron hybrids and Citrus relatives. Color expression depends on external factors and also on developmental stage. The coloration of stamen and style is citron-specific, while a red stigma is exclusive to Moro orange and its hybrids. Conclusion: It is hypothesized that there is a relationship among Citrus species and genes controlling anthocyanin pigmentation.

Sweet oranges are an important source of ascorbic acid (AsA). In this study, the content of AsA in the juice and leaves of four orange clonal selections, different in terms of maturity time and the presence/absence of anthocyanins, was correlated with the transcription levels of the main genes involved in the biosynthesis, recycling, and degradation pathways. Within each variety, differences in the above pathways and the AsA amount were found between the analysed tissues. Variations were also observed at different stages of fruit development and maturation. At the beginning of fruit development, AsA accumulation was attributable to the synergic action of l-galactose and Myo-inositol, while the l-gulose pathway was predominant between the end of fruit development and the beginning of ripening. In leaves, the l-galactose pathway appeared to play a major role in AsA accumulation, even though higher GalUr isoform expression suggests a synergistic contribution of both pathways in this tissue. In juice, the trend of the AsA content may be related to the decrease in the transcription levels of the GME, GDH, MyoOx, and GalUr12 genes. Newhall was the genotype that accumulated the most AsA. The difference between Newhall and the other varieties seems to be attributable to the GLDH, GalUr12, APX2, and DHAR3 genes.

Olive knot disease (OKD) induced by the bacterium Pseudomonas savastanoi pv. savastanoi seriously affects olive production in the Mediterranean basin. Nowadays, the only strategies to control the disease are pruning and the application of cupric products. An essential strategy to enhance protection is represented by the identification of resistant cultivars, which represents a crucial opportunity for future investments and breeding. We undertook a three-year-long survey at the International Olive Germplasm Collection of “Villa Zagaria” (Sicily, Italy) on thirty-six Sicilian cultivars that were monitored for symptom development. Cultivars with different levels of susceptibility were divided into five clusters. Moreover, in order to investigate possible interactions with endophytic microbial communities, two cultivars with contrasting susceptibilities, Zaituna (highly resistant) and Giarraffa (highly susceptible), were selected for an amplicon-based metagenomic analysis. Distinct endophytic communities colonized the two cultivars, suggesting an interaction between the resident bacterial community and the pathogen. Significantly higher bacterial richness was detected in the shoots of the susceptible cv. Giarraffa, although it had lower diversity. The opposite trend was observed for fungal communities. Among the microbes resulted to be enriched in cv. Giarraffa, it is important to underline the presence of Pseudomonas among the bacterial genera, and Alternaria, Neofusicoccum, Epicoccum, Ascochyta, and Elsinoe among the fungal genera, which include many species often described as plant pathogens and biocontrol agents. Starting from this basic information, new strategies of control, which include breeding for resistance and integrated disease management, can be envisaged.

Citrus nurseries significantly increase production costs due to the application of strictly technical and sanitary protocols. The growth media used are generally based on peat, a limited resource that is becoming increasingly scarce and consequently more expensive. Among the alternatives to peat is biochar, which could constitute a valid growing medium component for citrus seedling production. Three growth media were compared, each containing 50% sandy volcanic soil and the remaining 50% being: (i) biochar 50%; (ii) black peat 25% + biochar 25%; and (iii) black peat 25% + lapillus 25% as the control. The impact on the agronomic performance of citrus seedlings was assessed, and the involvement of specific genes in macronutrient uptake was evaluated. Destructive and molecular analyses were performed on leaves and roots during two different periods of the year: February and April. Based on physicochemical parameters and seedling growth, it can be assumed that peat can be partially substituted by conifer wood biochar in a total amount of 25 or 50%. A general comparison of the averages from the sampling and the various analyzed substrates revealed that in February, the evaluated genes involved in the absorption and transport of nutrients were differentially expressed in both leaves and roots, while in April, the expression was not consistent. Additionally, a general comparison between the analyzed tissues showed that, in most cases, expression was higher in the roots than in the leaves. Overall, a comparison among plants grown in different substrates indicated that the medium with 50% biochar displayed the highest expression levels.