Fernando Alves de Azevedo

Thirteen mandarin and hybrid cultivars grafted onto the commercial rootstocks Rangpur Lime and Swingle Citrumelo were comparatively assessed for vegetative growth, fruit physicochemical attributes, and field incidence and severity of Altenaria Brown Spot (ABS) and Huanglongbing (HLB). The experiment was conducted from January 2015 to December 2018 under a randomized block design, with ten replicates per scion–rootstock combination. Plant height, canopy volume, fruit mass, juice yield, acidity, soluble solids, and disease assessments were performed. RL induced greater vegetative growth but was associated with higher HLB severity, particularly in the Dekopon IAC 2009 and TM × LP 358 varieties. SC resulted in less vigorous trees but improved fruit quality, with higher acidity and soluble solids. Regarding ABS, the Loose Jacket IAC 515 and Muscia varieties showed high susceptibility, while Ortanique IAC 554 and Rainha BRS exhibited tolerance to both ABS and HLB. These findings suggest that although RL promotes vigorous growth, it may increase disease susceptibility, whereas SC is associated with reduced disease severity and improved fruit quality. Ortanique IAC 554 and Rainha BRS showed consistently low severity of ABS and HLB, combined with stable vegetative development and fruit quality, underscoring the importance of rootstock choice for guiding cultivar deployment in orchards under high disease pressure.

Citrus productivity is strongly influenced by water availability and rootstock selection. This study evaluated the physiological and productive responses of two commercial scion × rootstock combinations: Tahiti acid lime BRS EECB IAC Ponta Firme grafted onto the dwarfing trifoliate rootstock IAC 718 Flying Dragon (PF_FD), and IAC 10 grafted onto the semi-dwarfing citrandarin IAC 3152 Itajobi (10_152). Field experiments were conducted over three years (2022–2024) under three irrigation regimes—variable (VIS), fixed (FIS), and non-irrigated (NIS)—using a 3×2 factorial design with randomized blocks and drip irrigation. Physiological parameters (root length, leaf water potential, gas exchange, proline, and lipoperoxide content) and productive traits (fruit quality and cumulative yield) were assessed. The 10_152 combination showed superior root development, gas exchange performance, antioxidant regulation, and fruit yield, particularly under FIS and NIS, indicating enhanced drought tolerance. In contrast, PF_FD performed well only under VIS and was more sensitive to water deficit. Principal component analysis revealed that higher productivity and resilience were associated with greater root length, increased proline accumulation, higher CO2 assimilation, and reduced oxidative stress. Furthermore, FIS irrigation was as effective as VIS in sustaining plant performance, while optimizing water use, suggesting a sustainable management strategy. Although Tahiti acid lime IAC 10 demonstrates vigorous early orchard growth, its susceptibility to wood pocket restricts its commercial use. Overall, citrandarin IAC 3152 Itajobi proved to be the most promising rootstock, suitable for both irrigated and non-irrigated orchards, whereas PF_FD is recommended only under optimal water conditions.

The selection of new mandarin varieties to enhance fruit supply and address phytosanitary challenges is a significant issue in table citrus farming. In Brazil, the primary harvest season for commercial varieties spans from May to August, leaving a gap in the availability of mandarins during the off-season, which typically coincides with the hottest months of the year. Furthermore, diseases such as Alternaria Brown Spot (ABS) and HLB have reduced planted areas due to the complexities of management and increased production costs. This study evaluated three new mandarin hybrids based on tolerance for ABS, their physicochemical properties and acceptance. Although citrus researchers’ experts of mandarins conducted the sensory characterization, the methodology reflects sensory descriptions grounded in consumer perception. Providing detailed data for each mandarin hybrid is crucial, as the varieties exhibit distinct characteristics that influence overall evaluations and help align each hybrid with consumer expectations. The results demonstrate that, despite variations in acceptance among evaluators for one or more attributes ranking from “slightly liked” to “liked a lot,” all hybrids were generally well received. Such studies are vital for guiding the selection of new mandarin varieties in genetic improvement programs.

The increasing incidence of diseases in tangerine orchards, including alternaria brown spot (ABS) caused by Alternaria alternata, has led to significant production losses, which requires the development of new disease control strategies. This study aimed to evaluate the effect of essential oils (EOs)extracted from the peels of different lemon genotypes at several concentrations and application methods on the ABS control. The experiments were conducted at the Sylvio Moreira Citrus Research Center, Cordeiropolis - São Paulo state,Brazil. An in vitro experiment was set up in a completely randomized design (CRD) with a 2×4×5 factorial scheme, including two control methods (preventive and curative),four lemon genotypes for EO extraction (Amber IAC 269, Eureka IAC 644, Harvey IAC 641 e IAC 262 Siciliano), and five EO concentrations (0, 2, 4, 8, and 16µL mL-1), with three replicates. Each replicate consisted of a Petri dish containingthree young Murcott tangor leaves. An in vivo experiment was also conducted in a CRD with a 2×4×3 factorial scheme, including two control methods (preventive and curative), four lemon genotypes for EO extraction, and three EO concentrations(0,8, and 16 µL mL-1), with three replicates. Each replicate consisted of one Murcott tangor plant, with four leaves from three different branches of the same plant.Disease severity assessments were conducted over seven days following fungal inoculation. The Area Under the Disease Progress Curve (AUDPC) was calculated using severity data. Data were submitted to analysis of variance, Tukey’s test(p<0.05), and regression analysis. The preventive method was more effective in controlling the fungus. The Amber genotype, at concentration of 16 µL mL-1,showed the best ABS control.

Sour rot, caused by Geotrichum citri-aurantii, is a significant post-harvest disease in citrus, resulting in economic losses due to the lack of effective fungicides. This study investigates the antifungal activity of citrus essential oils in controlling sour rot in Tahiti acid lime fruits. Essential oils were extracted via hydrodistillation with chemical composition analyzed by CG-MS and tested in vitro and in vivo. In vitro assays evaluated mycelial growth inhibition at 2 to 32 µL mL⁻¹ concentrations. In vivo trials involved preventive and curative treatments on artificially inoculated fruits stored at 25 °C ± 2, and the results showed that Pera IAC sweet orange oil, at 32 µL mL⁻¹, reduced disease severity by 96% in curative treatments. In contrast, Late IAC 585 willowleaf mandarin oil demonstrated moderate inhibition (44%) at the highest concentration in vitro. The oils did not affect key fruit quality parameters such as juice yield and total soluble solids. These findings suggest that citrus essential oils could be natural alternatives to synthetic fungicides for post-harvest sour rot management, combining effectiveness with maintaining fruit quality.

Sour rot, caused by Geotrichum citri-aurantii, is a significant post-harvest disease in citrus, resulting in economic losses due to the lack of effective fungicides. This study investigates the antifungal activity of essential oils from Late IAC 585 willowleaf and Pera IAC sweet orange in controlling sour rot in Tahiti acid lime fruits. Essential oils were extracted via hydrodistillation and tested in vitro and in vivo. In vitro, assays evaluated mycelial growth inhibition at concentrations ranging from 2 to 32 µl ml⁻¹. In vivo trials involved preventive and curative treatments on artificially inoculated fruits stored at 25°C ± 2. Results showed that Pera IAC sweet orange oil, at 32 µl ml⁻¹, reduced disease severity by 96% in curative treatments. In contrast, Late mandarin oil demonstrated moderate inhibition (44%) at the highest concentration in vitro. The oils did not affect key fruit quality parameters such as juice yield and total soluble solids. These findings suggest that citrus essential oils could be natural alternatives to synthetic fungicides for post-harvest sour rot management, combining effectiveness with maintaining fruit quality. Further research is needed to explore the mechanisms of action and commercial application potential.

Root rot and gummosis caused by Phytophthora spp. are considered one of the most important citrus diseases in Brazil. Symptoms of Phytophthora spp. infection in citrus plants are associated with lesions on the bark at the base of the plant, roots, and even lower branches. Inappropriately performed cultural practices, such as excessive irrigation and practices that result in reduced aeration and soil drainage, favor the disease. The objective of this study was to evaluate the effect of Urochloa ruziziensis mulching provided by an ecological mower on the severity of Phytophthora nicotianae root rot and the development of citrus plants and their root system. The experiments were carried out under controlled conditions on Rangpur lime seedlings kept in pots containing soil from ‘Hamlin’ orange orchards with the use of an ecological mower or a conventional mower in the management of inter-row vegetation for six years. Urochloa ruziziensis mulching (9 t ha⁻¹) was added or not to the pots. The inoculation of P. nicotianae in the roots occurred through infection of the soil with a solution containing mycelium and sporangia of the pathogen. A 2 × 2 × 2 factorial scheme was used, with the following factors A: soil type, B: inoculation of P. nicotianae and C: mulching of U. ruziziensis. The attributes of plant development, such as root growth, average number of leaves, leaves and dry mass of shoots and roots, in addition to assessments of the severity of disease in the roots, were evaluated. The mulch of U. ruziziensis did not promote an increase in root rot. The soil resulting from this management promoted the better development of Rangpur lime plants. Therefore, vegetation management of inter-row with an ecological mower is not associated with increased symptoms of Phytophthora root rot.

Glyphosate is the most widely used herbicide for weed control in citrus orchards in Brazil; therefore, it is likely that several species have gained resistance to this herbicide and that more than one resistant species can be found in the same orchard. The objective was to identify weeds resistant to glyphosate in citrus orchards from different regions of the São Paulo State (SP) and determine how many resistant species are present within the same orchard. Seeds of Amaranthus deflexus, A. hybridus, Bidens pilosa, Chloris elata, Conyza bonariensis, Digitaria insularis, Solanum Americanum, and Tridax procumbens, which, as reported by growers, are suspected to be resistant to glyphosate, were collected from plants that survived the last application of this herbicide (>720 g of acid equivalent [ae] ha^–1) in sweet orange and Tahiti acid lime orchards. Based on dose–response and shikimic acid accumulation assays, all populations of A. deflexus, A. hybridus, B. pilosa, and T. procumbens were sensitive to glyphosate. However, populations of B. pilosa from the Olimpia region (R-NS, R-PT and R-OdA) showed signs of resistance based on plant mortality rates by 50% within a population (LD₅₀ = 355–460 g ae ha⁻¹). All populations of C. bonariensis, C. elata, and D. insularis were resistant to glyphosate, presenting resistance ratios from 1.9 to 27.6 and low shikimate accumulation rates. Solanum americanum also showed resistance, with resistance ratios ranging from 4.3 to 25.4. Most of the citrus orchards sampled presented the occurrence of more than one species resistant to glyphosate: Nossa Senhora—one species; Olhos D’agua and Passatempo—two species; Araras—four species; and Cordeiropolis and Mogi-Mirim—up to five species. The results reported in this paper provide evidence of multiple species in citrus orchards from São Paulo that have exhibited resistance to glyphosate. This underscores the difficulties in managing glyphosate-resistant weeds which are prevalent throughout the country, such as C. bonariensis and D. insularis. The presence of these resistant species further complicates the control of susceptible species that may also develop resistance. In addition, the glyphosate resistance of S. americanum was identified for the first time.

Mandarins occupy the third group among citrus produced in Brazil. Primarily aimed at the fresh fruit market, commercial orchards have suffered significant production losses due to the high incidence of diseases, such as the alternaria brown spot (ABS) and huanglongbing (HLB). The fact that 80% of the orchards are composed of two varieties, Ponkan mandarin and Murcott tangor, which are highly susceptible to both diseases, demands intensive chemical control of the diseases in the field, which has resulted in a significant increase in production costs and a negative environmental impact. A total of one hundred and seventy-three mandarin accessions, including several species and hybrids belonging to the Collections of the Instituto Agronômico de Campinas (IAC), were evaluated in the field in an endemic location for the diseases. Evaluations of the incidence and severity of the diseases showed a range of genotypes tolerant to ABS that could replace the current commercial varieties, mainly within the clementine and willow leaf mandarin groups. Although, with differences in incidence and susceptibility to HLB, there are no tolerant varieties to this disease, which significantly impacts the loss of fruit quality.

Alternaria brown spot (ABS) is a disease caused by the fungus A. alternata f. sp. citri, which results in lesions on the fruits, leaves, and branches of several mandarin varieties and their hybrids. Due to the high cost of fungicide application, alternative methods for controlling ABS need to be studied. Therefore, this study aimed to evaluate the use of essential oils (EOs) from different mandarin varieties to mitigate the effects of ABS. The inhibitory effect of different concentrations (1, 2, 4, 8, and 16 μL·mL⁻¹) of the EOs of Fremont IAC 543 mandarin, IAC 2019Maria mandarin, Murcott IAC 221 tangor, and Late IAC 855 willowleaf on the in vitro mycelial growth of the fungus A. alternata was evaluated. Additionally, the curative and preventive effects of these EOs on the ABS symptoms in detached leaves of Murcott IAC 221 tangor were also assessed. The EO of IAC 2019 Maria mandarin induced less mycelial growth, and consequently, a greater inhibition of the growth of the fungus A. alternata at a concentration of 16 μL·mL⁻¹. This EO was more effective for control than the other oils tested. In the detached leaf experiment, both the curative and preventive treatments at a concentration of 16 μL·mL⁻¹ showed lower values of disease severity.