Citrus Orchards Research Articles

Spontaneous Plants Improve the Inter-Row Soil Fertility in a Citrus Orchard but Nitrogen Lacks to Boost Organic Carbon

The inter-row soils in conventionally run citrus orchards in Eastern Spain lose fertility, either physically, chemically, or biologically, as a consequence of machinery traffic and the use of herbicides. In order to regain inter-row soil fertility, two grass-cover management alternatives to the commonly used herbicide-kept bare management, namely, spontaneous plants and fescue, were established and left for four years until their effects on several physical, chemical, and biological parameters were monitored for two years more. The fescue ground cover exhibited lower average and maximum soil temperatures due to higher evapotranspiration rates but also higher annual soil water content on average and, additionally, higher rhizodeposition. Despite the fact that these new beneficial conditions helped enhance the soil’s biological fertility under fescue, the physical or chemical fertilities did not improve and neither did the organic carbon (SOC). The spontaneous plants also enhanced the biological fertility, but in this case, beneficial conditions were reflected by improvements in the chemical fertility, particularly the exchangeable potassium, and in the physical fertility by increasing the surface hydraulic conductivity and decreasing the bulk density. In the inter-rows of this citrus orchard, a seeded grass cover does not seem able to provide any soil fertility enhancement in comparison to a spontaneous one; rather the opposite. However, a lack of natural or man-driven nitrogen inputs poses a constraint to SOC gains. For this aim, the annual surface application of organic nitrogen-rich materials or even better, the fostering of N-fixing organisms would be recommended.

Influence of ground beetles (Carabidae) as biological agent to control of the Mediterranean fruit fly pupae, Ceratitis capitata, in Iranian citrus orchards

• High diversity and density of Carabidae observed with eliminated pesticide spray. • Instead pesticide, mineral oil spray led conserving the carabids species. • Seasonal density fluctuation of Carabidae was observed, increasing in spring. • Highest population of Carabidae with the peak of fruit fly damage in September. • H. rufipes, B. karelinii and Pterostichus macer were the most voracious predators. Damage by Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) in the northern Iranian citrus orchards has been led to spray by different chemical pesticides. The present study was conducted in the citrus orchard in Mazandaran province of Iran where with the exception of mineral oil treatments for scale insects, had not been sprayed with synthetic insecticides for six years. The purpose of this study was initially to investigate faun and seasonal activity of predaceous ground carabid beetles in the citrus orchards. Additionally, their role as predators of Ceratitis capitata (Wiedemann) pupae was evaluated under laboratory and field conditions. Predation in laboratory was evaluated by no choice feeding experiments while predation under field conditions was evaluated by molecular detection of the pest DNA in the gut contents of field-collected Carabids. A total of 3,437 beetles of ten carabid species were collected from a non-chemical treatment citrus orchard. The results of the seasonal density fluctuation indicated increasing population in spring reaching the highest in September, simultaneously with the peak of fruit fly damage, and thereafter decreasing during winter when the pest was overwintering. However, three species, Harpalus rufipes, Broscus karelinii and Brachinus brevicollis were most abundant in the field collection but the results of no-choice experiments in the laboratory indicated H. rufipes, B. karelinii and Pterostichus macer were the most voracious predators on pupae. Results of gut content analysis of the voracious species indicated the positive testing for pest DNA in 79.16 % of H. rufipes , 76.92% of B. karelinii and 75% of P. macer of analyzed beetles. The results of the study strongly indicated that in citrus orchards where intensive spraying is eliminated, natural enemies such as Carabid beetles could play an important role in reducing pests such as medfly.

Study of the population dynamics of phytoseiid mites on citrus under natural conditions

Citrus is the most extensively produced tree fruit crop in the world, and the citrus red mites, Panonychus citri (McGregor) and citrus rust mites, Phyllocoptruta oleivora (Ashmead) are the serious pest mites of citrus crops. Except for chemical control, biological control is an important component of integrated pest management and plays an essential role in regulating populations of pest mites. Predatory mites from the family Phytoseiidae are important natural enemies. The populations of P. citri are usually controlled by indigenous predators, mainly the phytoseiid mites. As native phytoseiids are more likely to adapt to the local environmental conditions than the commercially available phytoseiids, conservation of local phytoseiid species is a key factor for the IPM success in citrus orchards. Investigation into the species and population dynamics of phytoseiid mites in citrus orchards will provide important references to the conservation and utilization of predatory mites. This work aimed to investigate the species of phytoseiid mites and their seasonal population dynamics associated with P. citri in different citrus cultivars orchards. We sampled phytoseiid mites from orchards planted with three citrus cultivars of citron-lemon, Ehime Kashi No. 28 and Shatangju, respectively, from April to December in 2018⁓2021. Species of phytoseiid mites, and their developmental stage and gender were identified under a microscope. In the citron-lemon orchard, we recorded nine phytoseiid species in 2018, but only three species in 2019. The dominant species was Scapulaseius newsami (Evans). In 2020, five species with a dominant species of Euseius nicholsi (Ehara et Lee) were found in Ehime Kashi No. 28 orchard, but only two with a dominant species of Neoseiulus californicus (McGregor) detected in the Shatangju orchard. In the Shatangju orchard in 2021, six species were recorded with N. californicus being dominant from April to July, and Amblyseius eharai Amitai & Swirski being dominant from August to December. The population of predatory mites peaked in May and October in the citron-lemon orchard, and in May, July and October in the Ehime Kashi No. 28 and Shatangju orchards. All active life stages (i.e., larva, nymph and adult) were found and most were adults. The sex ratio was female-biased (over 80%) in each orchard. In conclusion, the population size of phytoseiids changed over the growing seasons. Whether this could be attributed to the different tolerance capacities of different species to the local climate conditions or chemical pesticides remains for future studies.

Brevipalpus (Tenuipalpidae) and orchid fleck virus (OFV) in South Africa: what do we know?

Certain species of Brevipalpus (Trombidiformes: Tenuipalpidae) are able to transmit viruses of the citrus leprosis complex, a serious non-systemic disease of citrus. This disease is endemic to Central and South America, and is characterised by necrotic lesions with chlorotic halos on twigs, leaves and fruit. Citrus leprosis is caused by two types of RNA viruses: cytoplasmic (CL-C) and nuclear (CL-N). In South Africa, CL-N symptoms were detected in 2018 in citrus orchards in the Sundays River Valley (SRV) of the Eastern Cape (Fig 1), and found to be associated with trees testing positive for orchid fleck virus (OFV) (Cook et al. 2019). Mites from this site identified as B. californicus s.l. tested positive for OFV. It is assumed that the entry pathway of OFV virus into South Africa was via the trade of orchid pot plants, and that it was then transmitted to citrus by viruliferous B. californicus. This is the first CL virus-vector association and putative transmission from orchids to citrus identified in South Africa.

Resistance management for mites vectoring citrus leprosis in Brazil

Citrus leprosis is the most important viral disease affecting Brazilian citrus orchards. The disease is caused by the cilevirus citrus leprosis virus C (CiLV-C) and transmitted by flat mites Brevipalpus yothersi Baker (Acari: Tenuipalpidae). Citrus leprosis can reduce yield by causing premature fruit drop, defoliation, and drying of branches of citrus trees.

First Record of Aspergillus fijiensis as an Entomopathogenic Fungus against Asian Citrus Psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae).

The Asian citrus psyllid Diaphorina citri Kuwayama (Hemiptera: Liviidae) is the most widespread and devastating pest species in citrus orchards and is the natural vector of the phloem-limited bacterium that causes Huanglongbing (HLB) disease. Thus, reducing the population of D. citri is an important means to prevent the spread of HLB disease. Due to the long-term use of chemical control, biological control has become the most promising strategy. In this study, a novel highly pathogenic fungal strain was isolated from naturally infected cadavers of adult D. citri. The species was identified as Aspergillus fijiensis using morphological identification and phylogenetic analysis and assigned the strain name GDIZM-1. Tests to detect aflatoxin B1 demonstrated that A. fijiensis GDIZM-1 is a non-aflatoxin B1 producer. The pathogenicity of the strain against D. citri was determined under laboratory and greenhouse conditions. The results of the laboratory study indicated that nymphs from the 1st to 5th instar and adults of D. citri were infected by A. fijiensis GDIZM-1. The mortality of nymphs and adults of D. citri caused by infection with A. fijiensis increased with the concentration of the conidial suspension and exposure time, and the median lethal concentration (LC50) and median lethal time (LT50) values gradually decreased. The mortality of D. citri for all instars was higher than 70%, with high pathogenicity at the 7th day post treatment with 1 × 108 conidia/mL. The results of the greenhouse pathogenicity tests showed that the survival of D. citri adults was 3.33% on the 14th day post-treatment with 1 × 108 conidia/mL, which was significantly lower than that after treatment with the Metarhizium anisopliae GDIZMMa-3 strain and sterile water. The results of the present study revealed that the isolate of A. fijiensis GDIZM-1 was effective against D. citri and it provides a basis for the development of a new microbial pesticide against D. citri after validation of these results in the field.

Soil greenhouse gas emissions and crop production with implementation of alley cropping in a Mediterranean citrus orchard

The implementation of alley cropping in orchards has been suggested as a sustainable strategy to increase farmer revenues by crop diversification, enhance soil organic matter (SOM) and fertility, water retention, overall biodiversity, and contribute to climate change mitigation. Thus, the objective of this study was to assess if alley cropping with annual crops can contribute to i) mitigate soil greenhouse gas (GHG) emissions, ii) enhance C sequestration in a semiarid Mediterranean irrigated citrus orchard, and iii) increase land productivity. For this, two different treatments were established: i) conventional mandarin monoculture (MC) with no alley cropping; and ii) mandarin diversified with alley cropping of barley/vetch and fava bean (DIV). Measurements of soil CO2 and N2O emissions were periodically performed (every 7–20 days) during two years. Soil CO2 emission rates followed the soil moisture trend, and showed no significant differences between treatments. As an average, soil CO2 emission rates were 147 mg m-2 h-1 in MC and 196 mg m-2 h-1 in DIV. Soil N2O emission rates were not correlated to soil moisture nor temperature, and showed average values of 0.026 mg m-2 h-1 in MC and − 0.002 mg m-2 h-1 in DIV. Alley cropping did not contribute to significantly increase soil organic C and total nitrogen in two years’ time. With regard to production, mandarin yield showed no significant differences between treatments, but alley crops contributed to complementary commodities to the main cash crop, increasing overall land productivity. Thus, alley cropping in irrigated Mediterranean orchards has no significant effect on soil C sequestration and GHG emissions at short-term, with increased land productivity owing to new commodities grown in the alleys. These results confirm that under semiarid Mediterranean climate, long periods are needed to efficiently assess soil C sequestration potential of sustainable practices in orchards.

First detection of resistance to deltamethrin in Spanish populations of the Mediterranean fruit fly, Ceratitis capitata

The control of the Mediterranean fruit fly (Medfly), Ceratitis capitata, in citrus orchards in Spain is mainly based in three insecticides (spinosad, lambda-cyhalothrin and deltamethrin) and the liberation of sterile males. However, Medfly control is compromised by the development of lambda-cyhalothrin resistance and the detection of spinosad-resistant alleles in field populations. We report here, for the first time, resistance to deltamethrin in populations collected in fields under different management strategies, including MagnetMed™ traps coated with this insecticide and/or spinosad and lambda-cyhalothrin used as bait sprays, and even in populations obtained from non-treated fields. Two deltamethrin-resistant strains (BP-delta and Rfg-delta) were generated from the descendants of some of the field populations that showed lower susceptibility to deltamethrin. Both strains showed low susceptibility to MagnetMed™ traps, moderate susceptibility to Ceratipack traps, and lacked cross-resistance to spinosad and lambda cyhalothrin. Our data suggest that deltamethrin resistance was mediated by P450 enzymes, since bioassays with synergists showed that PBO reverted resistance in a field population and the laboratory strains, whereas the effect of DEF and DEM was minor and no mutations were found in the VGSC gene. The inheritance of resistance for both strains was completely recessive, autosomic and did not fit the mortality expected for a recessive character under a monogenic or digenic model. We also found that deltamethrin resistance presented a fitness cost in terms of males’ weight, males’ and females’ longevity and lifetime fecundity, with a more pronounced effect in the BP-strain than in the Rfg-delta strain. Our results highlight the need to implement insecticide resistance management strategies to prevent control failures.

A low-toxicity baiting program precipitates collapse of Argentine ant and ant-associated hemipteran pest populations in commercial citrus

The Argentine ant, Linepithema humile Mayr (Hymenoptera: Formicidae), disrupts biological control agents which induces population outbreaks of honeydew-producing hemipteran pests infesting agroecosystems. A multi-season liquid baiting program was evaluated for control of L. humile and ant-associated hemipteran pests in six commercial citrus orchards in southern California. Ant activity in treated trees fell by 96% within three months of treatment and was, on average, 95% lower in treated plots than untreated plots across the 18-month study period. Ant control resulted in the near elimination of hemipteran pest populations on trees in treated plots. Pre- and post-treatment estimates indicated that hemipteran pest infestation of twigs, flush, and fruit decreased by 97, 84, and 99% one year after treatment, respectively. Furthermore, cumulative infestation frequency was 10 times lower and cumulative colony size was 5 times lower on treated trees than control trees across the final year of study. Examining individual hemipteran pest species, the mean infestation rate by Diaphorina citri Kuwayama (Hemiptera: Liviidae) was 75% lower, Coccus hesperidum L. (Hemiptera: Coccidae) 95% lower, Planococcus citri Risso (Hemiptera: Pseudococcidae) 98% – 100% lower, and Aonidiella aurantii Maskell (Hemiptera: Diaspidae) 70 – 80% lower in treated trees relative to untreated trees. A surge in generalist predator activity and parasitism following ant bait deployment appear to be the driving forces behind the marked decrease in pest infestation observed in treated trees. Results underscore the importance of L. humile control for integrated pest management programs targeting ant-associated hemipteran pests in commercial citrus.

Population Dynamics of Arthropods in New Caledonian Citrus Orchards

Aims: Agroecological infrastructures are central to the preservation of arthropod populations and ecosystem services associated. There is little data on the population dynamics of New Caledonian citrus orchards. Thus, this study focuses on the response of arthropods to four management methods in the orchard: conventional management, inter-row vegetated, row mulching and edge windbreaks.
 Place and Duration of Study: This study was conducted in the village of La Foa in New Caledonia. It took place over three months, from the end of February to the end of May 2022.
 Methodology: To collect the greatest possible diversity of insects, four complementary trapping methods were used: pitfall traps, yellow plates, Malaise traps and sweeping nets. Once collected, the trapped insects are then sorted and identified. The sorting is done with a binocular magnifying glass. Insects are identified using specific determination keys, documentation, or with the help of the Reference Collection of Terrestrial Invertebrates of New Caledonia - Xavier Montrouzier (CXMNC). When identification is not immediately possible, a morphotype number is assigned. For each species and morphospecies, a photograph is taken. Alpha and beta diversity was studied using rarefactions, Shannon index and Generalized Linear Models.
 Results: A positive effect of agroecological infrastructures on insects’ abundance and diversity was recorded. In contrast, low arthropod abundances and diversities were presented in the orchard under conventional management (P < 0.001). Mulching management was the parameter showing the much higher insects’ abundance. Moreover, populations dynamics were generally correlated with the related infrastructures. Thus, windbreaks acted as ecological corridors and the inter-row vegetation as refuge habitats for beneficial insects. 
 Conclusion: These results demonstrate the damage of conventional agriculture on arthropod diversity in New Caledonian orchards. They also show that agroecological infrastructures can bring back insect biodiversity, especially with the mulching management.

Geographic Location, Management Strategy, and Huanglongbing Disease Affect Arbuscular Mycorrhizal Fungal Communities Across U.S. Citrus Orchards

The benefits of arbuscular mycorrhizal fungi (AMF) to agroecosystems have been well recognized. Citrus is a globally grown fruit tree commonly found in association with AMF. Global citrus production is currently under the threat of the pandemic huanglongbing (HLB) disease. Since its introduction in the United States, the disease has devastated the Florida citrus industry and is now at the doorsteps of commercial orchards in California. Here, we tested how the two distinct climatic zones within the continental United States where citrus is mostly grown (California and Florida) influenced AMF community diversity and composition. We also assessed in what capacity low-input organic farming and HLB disease affected the AMF communities colonizing the citrus roots. Root samples were collected from 88 trees across 10 orchards. Orchards were selected based on conventional or organic practices in California and based on HLB symptom severity in Florida. AMF communities were characterized using high-throughput sequencing of the small-subunit ribosomal RNA gene. Taxa names were assigned based on a phylogenetic analysis that comprised a backbone of AMF reference sequences from Mycobank and virtual taxa from the MaarjAM database. AMF were detected in 78% of citrus root samples, with taxa belonging to six genera ( Dominikia, Funneliformis, Glomus, Rhizophagus, Sclerocystis, and Septoglomus) and unknown Glomeraceae genera. Geographical location, management practice, and disease affected AMF community composition. We provide evidence that perennial agroecosystems are composed of generalist and specialist AMF taxa comparable with other ecosystems and identified ubiquitous taxa that could potentially be exploited for agricultural purposes.

Decision support strategy for preventing sunburn: Precise prediction of sunburn occurrence reflecting both biotic and abiotic factors in late-maturing citrus orchards

This study emphasized not only the basic concept that the sunburn of fruit was caused by fruit skin temperature rising above its tolerable threshold but also that the threshold was variable, namely, fruit became more vulnerable to sunburn on its own as the growth period progressed. These main results were derived from two major functions: first, multiple linear regression to estimate the fruit skin temperature utilizing solar radiation and ambient air temperature, and second, nonlinear regression with a sigmoid function, which represents the variability in the fruit skin temperature threshold inducing sunburn. The specific major results are as follows. Both individual and multiple regressions showed that the increase in fruit skin temperature was more affected by solar radiation than by ambient air temperature. Considering the entire period from July to September, sunburn was related to fruit skin temperatures above 46 °C. However, the specific investigation dividing the entire period into 10-day periods indicated that the fruit skin temperature threshold for inducing sunburn decreased over time. In the discriminant analysis for predicting the occurrence of sunburned fruits, the prediction accuracy based on the variable threshold was 81.9%, which was higher than 67.0% based on the fixed threshold of 46 °C. The reference ambient air temperature for the occurrence of sunburn decreased with seasonal progress in the field from higher than 35 °C in early August to 28 °C in mid-September and in the greenhouse from higher than 39 °C to 31.7 °C. The variability of thresholds related to the internal tolerance of fruit for sunburn presented the reason why sunburned fruits could occur or increase despite the weakening of abiotic factors inducing sunburn, such as solar radiation and ambient air temperature, as the season progresses from summer to autumn.

Native Rhizobia Improve Plant Growth, Fix N2, and Reduce Greenhouse Emissions of Sunnhemp More than Commercial Rhizobia Inoculants in Florida Citrus Orchards.

Sunnhemp (Crotalaria juncea L.) is an important legume cover crop used in tree cropping systems, where there is increased interest by growers to identify rhizobia to maximize soil nitrogen (N) inputs. We aimed to isolate and identify native rhizobia and compare their capabilities with non-native rhizobia from commercial inoculants to fix atmospheric dinitrogen (N2), produce and reduce nitrous oxide (N2O), and improve plant growth. Phylogenetic analyses of sequences of the 16S rRNA and recA, atpD, and glnII genes showed native rhizobial strains belonged to Rhizobium tropici and the non-native strain to Bradyrhizobium japonicum. Plant nodulation tests, sequencing of nodC and nifH genes, and the acetylene-dependent ethylene production assay confirmed the capacity of all strains to nodulate sunnhemp and fix N2. Inoculation with native rhizobial strains resulted in significant increases in root and shoot weight and total C and N contents in the shoots, and showed greater N2-fixation rates and lower emissions of N2O compared to the non-native rhizobium. Our results suggest that native rhizobia improve plant growth, fix N2, and reduce greenhouse emissions of sunnhemp more than commercial rhizobia inoculants in Florida citrus orchards.

Influence of Temperature Variability on Survival and Development of Citrus Leaf Miner, Phyllocnistis citrella Stainton (Lepidoptera: Gracilariidae) in Tanzania

Due to limited information on Phyllocnistis citrella’s Biology, study was aimed to examine the effects of different temperature levels on biology of citrus leaf miner under controlled laboratory conditions at the Entomology laboratory of Sokoine University of Agriculture (SUA), Tanzania from December 2011 to September 2012. Leaf samples (1,985 leaf samples) considered to contain larvae in serpentine mines were collected and individually incubated at room temperature. The emerging adults were wet preserved in 70% ethanol while some dry preserved using special micro pins under microscope for future identification. A Monterey LG8920 pheromone trap was set in every 10m2 at SUA citrus orchard to trap adult moths to supplement sample sources. Citrus leaf miners species collected were identified and four different temperature levels (20, 25, 30 and 35°C) were monitored at each developmental stage. Results revealed longer development time (egg to adult) at 200C and shorter at 300C in 28 and 10 days while the total mortality was 26.67% at 200C and 6.67% at 300C respectively. Oviposition period and rate were negatively and positively influenced by temperature (from 9.26 days at 200C to 6.21 days at 300C and 15.2 eggs/ female/ day at 300C and 6.8 eggs/ female/ day at 200C respectively). The overall fecundity was 28.2 eggs/ female at 200C and 57.1 eggs/ female at 300C. High larval mortality rate was recorded compared to the egg stage while no mortality observed at pupa stage. Conclusively, the pest on this temperature range (200C, minimum to 300C, maximum) has high fecundity, low mortality rate and the developmental time was positively correlated with high temperature, therefore considered optimum temperature range for its survival and development. Other researches especially Integrated Pest management are imperative for sound management package as per the pest in Tanzania and beyond.

Contributions to the knowledge of the Cicadellini sharpshooters (Hemiptera: Cicadellidae) associated with citrus orchards in Argentina

Xylella fastidiosa Wells et al. is a xylem-borne bacterium that causes some of the most important plant diseases to woody plants such as citrus, olives, almonds and other cultures. This pathogen is mainly transmitted by sharpshooters, among which the tribe Cicadellini (Cicadellinae) includes the largest number of proven vectors. The correct identification of the vectors, along with biological and phenological information, are necessary to identify the key vectors involved in the spread of the bacterium and, consequently, establish control strategies and evaluate risks at a local or regional scale. However, lack of information on the Cicadellini from Argentina has delayed the implementation of control measures. Based on surveys conducted in the main citrus producing areas along with bibliographic data, this contribution provides the first list of Cicadellini species from Argentina that are potential vectors of X. fastidiosa; an identification key to these sharpshooters is provided. Twelve species were recorded from northeastern citrus groves, while from northwestern orchards, with previous information totally absent, 10 species were recorded. Eight species are shared by all producing regions, and five of them are proven vectors of X. fastidiosa (Bucephalogonia xanthophis (Berg), Dilobopterus costalimai Young, Macugonalia cavifrons (Stål), M. leucomelas (Walker), Sonesimia grossa (Signoret)). This contribution provides 22 new insect-plant relationships, information on their natural enemies, the geographic distribution of all species is broadened and the female genitalia of three proven vectors are described for the first time.

Assessment of crop evapotranspiration and deep percolation in a commercial irrigated citrus orchard under semi-arid climate: Combined Eddy-Covariance measurement and soil water balance-based approach

An accurate estimate of crop coefficient (Kc) values at different development stages (Kcini, Kcmid, and Kcend) is crucial for assessing crop water requirements in semi-arid regions. The objectives of this study were first to quantify the reference evapotranspiration (ETo) and to calculate the actual evapotranspiration (ETa) over citrus in a semi-arid climate under drip irrigation. For this purpose, a site of a citrus orchard in Souss-Massa, planted with the Esbal variety of clementine, was equipped with an Eddy-Covariance (EC) system, and sensors to measure radiation, soil heat flux, and micrometeorological forcing data, during 2020 and 2021 seasons. Also, the soil moisture content at various soil depths in the root zone near the EC tower was monitored. The energy balance closure (EBC) approach was adopted for flux assessment to ensure a quality check for the EC measurements. The obtained EBCs were about 82% and 79% for the daily measurements in 2020 and 2021, respectively, which can be considered acceptable considering the nature of the citrus orchard (relatively tall and sparse). Second, the study aimed to estimate actual Kc act values for citrus under the same irrigation strategy. The derived values were compared to different recommended Kc values in the literature. In the third stage, this work aimed to offer an alternative plan to sustainable irrigation management by elaborating an irrigation schedule for citrus crops in the region using the FAO-56 simple approach to avoid water stress and deep percolation (i.e., Ks = 1 and DP = 0). Eventually, an irrigation schedule was drawn following the crop’s phenological stages. The seasonal mean citrus evapotranspiration (ETa) values are 1.68, 3.02, and 1.86 mm/day for the initial, mid, and end-season. The seasonal actual Kc act values were 0.64, 0.58, and 0.64 for Kcini, Kcmid, and Kcend, respectively. Additionally, the application of the water balance equation revealed that a large quantity of water is lost through deep percolation (52% of total water supplied). The study focuses on Citrus trees being a strategic crop with important socio-economic values in the Souss-Massa region. Thus, the results should support both scientists and farmers in planning and strategy development.

Fruit Characteristics of Citrus Trees Grown under Different Soil Cu Levels.

The effects of the increased soil copper (Cu) on fruit quality due to the overuse of Cu agents have been a hot social issue. Seven representative citrus orchards in Guangxi province, China, were investigated to explore the fruit quality characteristics under different soil Cu levels and the relationship between soil-tree Cu and fruit quality. These results showed that pericarp color a value, titratable acid (TA), and vitamin C (Vc) were higher by 90.0, 166.6, and 22.4% in high Cu orchards and by 50.5, 204.2, and 55.3% in excess Cu orchards, compared with optimum Cu orchards. However, the ratio of total soluble solids (TSS)/TA was lower by 68.7% in high Cu orchards and by 61.6% in excess Cu orchards. With the increase of soil Cu concentrations, pericarp color a value and Vc were improved, TA with a trend of rising first then falling, and TSS/TA with a trend of falling first then rising were recorded. As fruit Cu increased, pericarp color a value and TSS reduced and as leaf Cu increased, TSS/TA decreased while Vc was improved. Moreover, a rise in soil Cu enhanced leaf Cu accumulation, and a rise in leaf Cu improved fruit Cu accumulation. Fruit Cu accumulation reduced fruit quality by direct effects, leaf Cu improved fruit quality by direct and indirect effects. Soil Cu affected fruit quality by indirect effects by regulating leaf Cu and fruit Cu. Therefore, reasonable regulation and control of soil Cu concentrations can effectively increase pericarp color, sugar, and acid accumulation in citrus fruit.

Being prepared for huanglongbing disease of citrus: a simulation exercise workshop for contingency planning held in Valencia, Spain

AbstractContingency plans aim to ensure a rapid and effective response to an outbreak of a pest likely which is to have a major impact. Huanglongbing is a devastating disease of citrus not yet present in the European and Mediterranean Plant Protection Organization (EPPO) region. A simulation exercise workshop for contingency planning was held in Valencia, Spain over 3 days in October 2021 as part of the PRE‐HLB project funded by the European Union Horizon 2020 programme. In total, 49 experts from the EPPO region attended the workshop. Participants represented a range of stakeholders from citrus cooperatives, grower associations, nursery workers, citrus exporters, landscapers and gardeners, scientists, Regional Plant Health Authorities, National Plant Protection Organizations and the European Commission. Participants were split into five groups and each group acted as an outbreak management team for a scenario based on a finding of a quarantine pest. The scenario followed the first (fictitious) finding of Diaphorina citri (the insect vector of ‘Candidatus Liberibacter asiaticus’, a causal agent of huanglongbing) at a citrus orchard in Spain. As the scenario developed over a month time scale, each team had to organize themselves to manage a number of issues designed to mimic the development of an outbreak of huanglongbing of citrus over the course of the exercise. The groups acknowledged the usefulness of the Spanish contingency plans for huanglongbing and its vectors, the EPPO Standards, and the risk‐based surveillance design tool RiBESS+.

Mitigation of nutrient runoff loss using reduced nitrogen application and green manure planting in citrus orchard in Hubei, China

Mitigation of nutrient runoff loss using reduced nitrogen application and green manure planting in citrus orchard in Hubei, China

Preharvest Foliar Application of Si–Ca-Based Biostimulant Affects Postharvest Quality and Shelf-Life of Clementine Mandarin (Citrus clementina Hort. Ex Tan)

Citriculture and the postharvest industry are in the quest for biostimulants that favour fruit quality and extend shelf-life. Recently, Si has emerged as a biostimulant and its impact on fruit quality and postharvest shelf-life needs to be elucidated. The experiment is conducted for two consecutive years (2019 and 2020) in a commercial citrus orchard. In the present study, a Si–Ca-based product (Gravital® Force SC, AGROLOGY SA, Sindos, Greece) is foliar sprayed upon clementine mandarin (Citrus clementina Hort. Ex Tan cv. SRA 63) trees from August to November, while unsprayed trees are kept as controls. At commercial maturity, both sprayed and unsprayed fruits are harvested and stored for thirty (30) days at 5 °C with 90–95% relative humidity. Afterwards, they are kept at shelf temperature (20 °C) for six (6) days (shelf-life). At different intervals [at harvest, after cold storage (30 d at 5 °C), at the third day of shelf-life (30 d at 5 °C plus 3 d at 20 °C) and sixth day of shelf-life (30 d at 5 °C plus 6 d at 20 °C)], fruits are sampled and analysed for their qualitative characteristics. According to the results, the preharvest foliar application of the Si–Ca-based product delayed fruit maturation, increased peel firmness, total soluble content, total acidity, ascorbic acid, total phenols and antioxidant capacity, and reduced fruit decay during shelf storage. Results suggest that the preharvest foliar spray of Si–Ca products is able to maintain the postharvest quality of mid-ripening mandarin fruit.