Lorenzo Rossi

Cover crops are increasingly used by growers in the United States as an effective approach to enhance soil health. The interactions between cover crops and soil microbiomes have been studied extensively; however, research evaluating the impact of cover crops on rhizosphere microbial communities in tree crop systems, particularly under nutrient-limited field soils in Florida, remains limited. To address these knowledge gaps, a three-year field study was conducted to evaluate the effects of cover crop mixtures on soil bacterial and fungal communities in orchards of different citrus species and cultivars across seasons. The trial included ‘Star Ruby’ grapefruit trees grafted on ‘US-942’, ‘Bearss’ lemon trees grafted on ‘Sour Orange’, and ‘OLL-8’ sweet orange trees grafted on ‘US-942’ rootstock in a randomized complete block design comparing conventional management (no cover crop-control) with cover crop treatments. Bacterial community composition showed consistent taxonomic patterns across cultivars and treatments, with Proteobacteria consistently the most abundant phylum across grapefruit, lemon, and orange orchards, followed by Actinobacteriota, Acidobacteriota, and Firmicutes. Despite this overall stability, cultivar was the strongest determinant of bacterial community structure. Additionally, functional analysis revealed significant treatment-associated shifts in predicted guilds related to nitrogen transformations, carbon metabolism, sulfur oxidation, and manganese oxidation. In contrast, fungal community composition and predicted functional profiles were primarily structured by season, with limited effects of cultivar and cover cropping. Fungal communities were consistently dominated by Ascomycota across orchards, sampling dates, and treatments.

The use of cover crops in citriculture has become an increasingly popular grove management tool in Florida, especially in response to the challenges of low soil fertility and the detrimental diseas...

Citrus greening disease, also known as huanglongbing (HLB), is the most serious vector-borne bacterial disease of citrus worldwide and an emblematic case of perennial crop decline caused by insect vector–borne disease. There is an immediate global need to provide the citrus industry with relief from HLB and a return to profitable citrus production. Discovery of HLB treatments typically involve various laboratory-based assays, which then advance to greenhouse and eventually field testing in a workflow that takes multiple years. We present a field-forward experimental framework, “Grove-First,” that reverses the traditional laboratory-to-field pipeline by prioritizing outcome-based screening. Grove-First rapidly screens and validates treatments with regulatory-friendly profiles in commercial citrus groves using trunk injection to select treatments that improve tree health and fruit yield over the course of a single growing season. The Grove-First framework represents a generalizable systems approach for translational agricultural research, applicable to perennial crops where disease impact, long development timelines, and real-world variability demand in-field, outcome-based screening. Using this framework, we identified candidate treatments with effects comparable to or better than the standard oxytetracycline on visual tree-health and/or yield indices in an initial screen of HLB-positive 8-year-old ‘Valencia’ sweet orange trees. Expanded trials in commercial citrus groves allowed us to validate the initial screening results at other locations and in other citrus varieties. Grove-First rapidly accelerated the identification and large-scale field testing of HLB therapies, some of which are available for growers to use immediately and others that require further field testing and/or regulatory actions.

Citrus greening (Huanglongbing, HLB) continues to threaten citrus production in the United States, particularly in Florida, by impairing root growth and nutrient uptake. Concurrently, citrus producers are actively seeking alternatives to traditional chemical fertilizers, which raise concerns regarding soil sustainability. Organic amendments are widely used to improve soil organic matter (SOM) and overall soil health in agricultural systems across the United States. Among these amendments, biochar has gained attention for its potential to enhance soil fertility and plant productivity; however, questions remain regarding optimal application rates, particularly in sandy soils. Additionally, literature lacks clarity on how biochar influences citrus root system architecture across different rootstocks. This study evaluated the effects of biochar on citrus root system architecture and nutrient uptake across different rootstocks in the sandy soils. The primary objective was to determine which biochar application rate most effectively improved soil fertility and root development across different citrus rootstocks. Four citrus rootstocks (‘Sour Orange’, ‘Swingle’, ‘US-802’, and ‘US-942’) were grown for 5 months under controlled greenhouse conditions in native sandy soil amended with biochar at 0%, 10%, 20%, and 30% (v/v). The experiment followed a completely randomized design with six replications per treatment ( n = 6), each consisting of a single plant per pot. Root system architectural traits were quantified using WinRHIZO™ image analysis, and soil physicochemical properties along with soil and plant tissue nutrients were evaluated at harvest. The 20% biochar treatment significantly increased root length, volume, surface area, and average diameter across all rootstocks. Plant tissue analyses showed higher macronutrient concentrations, particularly in belowground tissues. Soil moisture content, soil organic matter, pH, and cation exchange capacity increased with the biochar rate, with the highest values observed with the 30% biochar rate. Moderate biochar application effectively enhanced nutrient availability and root system architecture of citrus rootstocks, demonstrating its potential as a sustainable soil amendment to improve fertility and root growth in nutrient-limited sandy soils.

As land salinization intensifies across the United States, there is growing interest in cultivating salt-tolerant crops such as olives ( Olea europaea ). With extra virgin olive oil becoming an increasingly popular and valuable commodity in the U.S. market, growing olive cultivars that can thrive under challenging conditions is critical. This study evaluated the physiological, antioxidative and biochemical responses of two relatively newly introduced olive cultivars, ‘Oliana’ and ‘Lecciana’, to salinity stress under controlled greenhouse conditions. Eight-month-old plants were subjected to three salinity treatments (0, 50, and 100 mM NaCl) in a completely randomized design ( n = 9). Plant gas exchange parameters were measured at 0, 15, 30, and 45 days after treatment, while chlorophyll content, fluorescence (Fv/Fm), biomass, nutrient accumulation (in leaves, stems, and roots), antioxidant enzyme activity, osmolyte levels, and reactive oxygen species (ROS) concentrations were assessed at 15, 30, and 45 days. Salinity stress significantly reduced gas exchange parameters in ‘Lecciana’ cultivar as compared to ‘Oliana’, resulting in decreased chlorophylls, Fv/Fm, and nutrient content. In response, antioxidant enzymes and osmolyte accumulation (proline and glycine betaine) increased with ‘Lecciana’ showing the strongest response. Conversely, lipid peroxidation and hydrogen peroxide (H ₂ O ₂ ) levels were highest in ‘Oliana’ under 100 mM NaCl, indicating greater oxidative stress. These findings suggest that ‘Lecciana’s high salinity tolerance is associated with enhanced antioxidant defense and compatible solutes. In addition, ‘Lecciana’ and ‘Oliana’ could be a promising cultivar for saline and drought-prone regions of the U.S., supporting the expanding production of high-quality extra virgin olive oil.

Salinity poses a significant challenge in horticulture, particularly for citrus, one of the most widely cultivated fruit crops. Soil bulk electrical conductivity levels above 1.4 dS/m can impair tree performance, reducing productivity and fruit quality. With increasing occurrences of extreme weather events and competition for fresh water, the identification of salinity-tolerant citrus cultivars is essential for sustainable production. This review examines citrus salinity tolerance trials, emphasizing cultivar selection, the use of grafted vs. nongrafted trees in experimental designs, and the role of the scion in salinity adaptation. Although most studies focus on rootstock influence, emerging evidence suggests that scions also regulate ion accumulation and stress responses. Research on salinity tolerance in citrus has expanded in recent years, with Spain, the United States, and Brazil leading investigations. Although arid and semiarid regions dominate salinity studies, in humid areas such as Florida there is also research interest due to the proximity of citrus production fields to coastal areas. The most frequently measured parameters in salinity trials include leaf and root ion concentrations, gas exchange, dry weight, and growth. A comprehensive assessment of salinity tolerance should integrate measurements that capture both osmotic stress and ion toxicity, including gas exchange, ion accumulation, dry weight, growth, chlorophyll fluorescence, and water/osmotic potential. Further research is necessary to optimize cultivar selection by evaluating both rootstock and scion contributions to salinity tolerance.