Huanglongbing (HLB) or citrus greening disease is the most severe citrus disease, devastating the industry worldwide. The presumed causal bacterial agent Candidatus Liberibacter spp. affects tree health as well as fruit development, ripening and quality of citrus fruit and juice. Fruit from infected trees can be either symptomatic or asymptomatic. Symptomatic fruit are small, asymmetrical and greener than healthy fruit. Furthermore, symptomatic fruit show higher titratable acidity and lower soluble solids, solids/acids ratio, total sugars and malic acid levels, lower ethyl butanoate, valencene, decanal and other ethyl esters, straight-chain aldehydes and sesquiterpenes, but higher in many monoterpenes compared to healthy and asymptomatic fruit. The disease also causes an increase in secondary metabolites in the orange peel and pulp, including hydroxycinnamic acids, limonin, nomilin, narirutin and hesperidin. Resulting from these chemical changes, juice made from symptomatic fruit is described as distinctly bitter, sour, salty/umami, metallic, musty, and lacking in sweetness and fruity/orange flavor. Those effects are reported in both Valencia and Hamlin oranges, two cultivars that are commercially processed for juice. The presumed HLB pathogen remains unconfirmed and its management is challenging due to the unpredictable latency times for symptoms after the tree has become infected, and the lack of effective curative treatment methods. When present, disease management depends on incidence rate, and relies on vector control, tree eradication, nutritional programs and use of plant varieties with increased tolerance. Earlier research showed that HLB-induced off-flavor was not detectable in juice made with up to 25% symptomatic fruit. In some production regions, it is increasingly difficult to find fruit not showing HLB symptoms. This review focuses on the effects of HLB on orange juice quality regarding chemical, physicochemical and biochemical characteristics, including levels of sugars, organic acids, secondary metabolites, levels and profiles of amino acids, bioactive amines, volatile compounds and sensory characteristics, as well as future research needs.

The substrate pH directly affects nutrient availability in the rhizosphere and nutrient uptake by plants. Macronutrients such as nitrogen, potassium, calcium, magnesium, and sulfur are highly available at pH 6.0–6.5, while micronutrients become less available at higher, alkaline pH (pH > 7.0). Recent research has indicated that low pHs can enhance nutrient uptake and improve sweet orange (Citrus sinensis) tree health. We designed a study to understand the influence of a wide range of substrate pH values on plant size and biomass, nutrient availability, leaf gas exchange, and rhizosphere microbiome of grapefruit (Citrus paradisi) affected by Huanglongbing (HLB). Two-year-old “Ray Ruby” grapefruit plants grafted on sour orange (Citrus aurantium) rootstock were cultivated indoors in 10-cm wide × 40-cm tall pots with peat:perlite commercial substrate (80:20 v/v). We tested two disease statuses [HLB-free or healthy (negative, HLB–) and HLB-affected (positive, HLB+)] and six substrate pH values (4, 5, 6, 7, 8, 9) in a 2 × 6 factorial arranged on a complete randomized design with four replications. The canopy volume of HLB+ plants was 20% lower than healthy plants, with pHs 7 and 9 resulting in 44% less canopy volume. The root and shoot ratio of dry weight was 25.8% lower in HLB+ than in healthy plants. Poor root growth and a decrease in fibrous roots were found, especially in pH 5 and 6 treatments in HLB+ plants (p < 0.0001). The disease status and the substrate pHs influenced the leaf nutrient concentration (p < 0.05). High substrate pH affects nutrient availability for root uptake, influencing the nutrient balance throughout the plant system. pH values did not affect plant photosynthesis, indicating that pH does not recover HLB+ plants to the photosynthetic levels of healthy plants—even though high pH positively influenced internal CO₂. There were collectively over 200 rhizobacterial identified by the 16S rRNA gene sequencing in individual phylogenetic trees. Most rhizobacteria reads were identified in pH 9. Our results indicated no effect of substrate pHs on the plant disease status induced by enhanced nutrient uptake.

Substrate volumetric water content (VWC) is a useful measurement for automated irrigation systems. We have previously developed automated irrigation controllers that use capacitance sensors and dataloggers to supply plants with on-demand irrigation. However, the dataloggers and accompanying software used to build and program those controllers make these systems expensive. Relatively new, low-cost open-source microcontrollers provide an alternative way to build sensor-based irrigation controllers for both agricultural and domestic applications. We designed and built an automated irrigation system using a microcontroller, capacitance soil moisture sensors, and solenoid valves. This system effectively monitored and controlled VWC over a range of irrigation thresholds (0.2, 0.3, 0.4, and 0.5 m ^3. m ⁻³ ) with ‘Panama Red’ hibiscus ( Hibiscus acetosella ) in a peat:perlite substrate. The microcontroller can be used with both regular 24-V alternating current (AC) solenoid valves and with latching 6- to 18-V direct current (DC) solenoid valves. The technology is relatively inexpensive (microcontroller and accessories cost $107, four capacitance soil moisture sensors cost $440, and four solenoid valves cost $120, totaling $667) and accessible. The irrigation controller required little maintenance over the course of a 41-day trial. The low cost of this irrigation controller makes it useful in many horticultural settings, including both research and production.

The UVI Commercial Aquaponic System is designed to produce fish and vegetables in a recirculating aquaculture system. The integration of these systems intensifies production in a small land area, conserves water, reduces waste discharged into the environment, and recovers nutrients from fish production into valuable vegetable crops. A standard protocol has been developed for the production of tilapia yielding 5 MT per annum. The production of many vegetable crops has also been studied but, because of specific growth patterns and differences of marketable product, no single protocol can be promoted. Each crop yields different value per unit area and this must be considered when selecting varieties to produce to provide the highest returns to the farmer. Variables influencing the value of a crop are density (plants/m2), yield (unit or kg), production period (weeks) and unit value ($). Combining these variables to one unit, $/m2/week, provides a common point for comparison among crops. Farmers can focus production efforts on the most valuable crops or continue to produce a variety of crops meeting market demand with the knowledge that each does not contribute equally to profitability

Citriculture is an important agricultural activity worldwide, occupying a relevant position in Brazil among fruit tree production for both the fresh fruit market and the processing industry for concentrated orange juice export. Recent advances in the country’s citrus nursery tree production system have been essential to guarantee the efficiency and competitiveness of Brazilian citriculture. The implementation of strict laws and regulations to produce trees in protected environments and improvements in production techniques for basic citrus propagation materials and nursery trees in São Paulo state has excluded the insect vectors of destructive diseases such as citrus variegated chlorosis and huanglongbing, making this an innovative reference system for citrus propagation around the globe. The main aspects of these advances are presented and discussed in this review, including advances in propagation techniques, scion and rootstock selection, genetic characterization and certification, tree size standards, cultural practices such as irrigation and fertilization for the production of citrus propagation materials and nursery trees, and nursery management tools.