Citrus Industry Research Articles

Safety risk of using asomate to reduce acid in Citrus production

Asomate, an organo-arsenic fungicide, was historically used on various crops. Recently, a type of pesticides capable of improving the sweet taste of Citrus fruit, was occasionally used to enhance the sweetness, taste, and accelerate the ripening of citrus fruits. The primary ingredient of the pesticides was confirmed to be asomate by elemental analysis, inductively coupled plasma mass spectrometry and high-resolution mass spectrometry analysis. To assess potential risks to Citrus quality and safety, field experiments were conducted on Harumi tangor by spraying the tree with the pesticide as the treated group and clean water as control. The effects of asomate on fruit quality and residue levels in fruits, leaves, and soil were investigated. Results showed that asomate decreased organic acid content in Citrus fruits by 60.5 %, while the sugar-acid and solid-acid ratios increased from 14.26 to 30.88, and from 16.15 to 35.50, respectively, implying for fruit quality with sweeter taste. Compared to the control, spraying of asomate has caused significant arsenic residues in the pesticide treated Citrus fruits (0.042 mg/kg vs 0.015 mg/kg), leaves (2.56 mg/kg vs 0.082 mg/kg), and soil (8.89 mg/kg vs 8.33 mg/kg), posing hazards to human health and the natural environment.

Phylogenetic and Pathogenic Evidence Reveals Novel Host-Pathogen Interactions between Species of Lasiodiplodia and Citrus latifolia Dieback Disease in Southern Mexico.

Mexico ranks second in the world for Persian lime (Citrus latifolia) exports, making it the principal citrus exporter within the national citrus industry, exporting over 600,000 tons per year. However, diseases are the main factor reducing production, resulting in significant economic losses. Among these diseases, fungal diseases like dieback, caused by species of Lasiodiplodia, are an emerging issue in Persian lime. Symptoms include gummosis, twig and branch dieback, cankers, the necrosis of bark and wood, fruit mummification, and tree decline. The aim of this study was to investigate the occurrence and pathogenicity of the fungal species associated with twig and branch dieback, cankers, and decline of Persian lime trees in southern Mexico, and to elucidate the current status of the Lasiodiplodia species causing the disease in Mexico. During June, July, and August of 2023, a total of the 9229 Persian lime trees were inspected across 230 hectares of Persian lime orchards in southern Mexico, and symptoms of the disease were detected in 48.78% of the trees. Branches from 30 of these Persian lime trees were collected. Fungal isolates were obtained, resulting in a collection of 40 strains. The isolates were characterized molecularly and phylogenetically through the partial regions of four loci: the internal transcribed spacer region (ITS), the β-tubulin gene (tub2), the translation elongation factor 1-alpha gene (tef1-α), and the DNA-directed RNA polymerase II second largest subunit (rpb2). Additionally, pathogenicity was assessed, successfully completing Koch's postulates on both detached Persian lime branches and certified 18-month-old Persian lime plants. Through multilocus molecular phylogenetic identification, pathogenicity, and virulence tests, five species were identified as causal agents: L. iraniensis, L. lignicola, L. mexicanensis, L. pseudotheobromae, and L. theobromae. This study demonstrates that in southern Mexico, at least five species of the genus Lasiodiplodia are responsible for dieback in Persian lime. Additionally, this is the first report of L. lignicola and L. mexicanensis as causal agents of the disease in citrus, indicating novel host interactions between species of Lasiodiplodia and C. latifolia.

Uses of Citrus Peels for Encouraging Food Nutrition: A Review

Orange peel (Citrus sinensis) belong to the family Rutaceae and it is well known promising source of multiple beneficial nutrients for human being. Global orange production is about 51 million metric tons. In India, area under citrus is 9.23 lakh hector which produces 86.08 lakh tones of fruits. Maharashtra is second largest state after Andhra Pradesh in the country and contributes to about 18.9 per cent to the total production of citrus in country. Orange peel obtains new healthy fruit products because peel friction has interesting and not very well known nutritional components such as Phenolic compound, Flavonoids, Dietary fiber. Part of orange such as peel and rind are used in food preparations. The peel of orange is use to make herbal tea, candied fruits peel and marmalade. Peels are regarded as waste material and is usually dried and ground to make citrus meal, a substitute cattle feed. Orange peels are also used as flavoring liqueurs, orange peel flavors is most desirable natural flavors. They are used in beverage, confectionery, bakery, pharmaceutical, cosmetic and perfumery industries. The citrus fruit residues, which are generally discarded as waste in the environment, can act as potential nutraceutical resources. Due to their low cost and easy availability such wastes are capable of offering significant low-cost nutritional dietary supplements in the form of orange peel powder in cookies. the orange peel powder waste used in various proportion viz, 0, 5, 10, 15, 20 per cent levels for incorporation in cookies by replacing the Maida in the basis of overall sensory attributes, cookies prepared with 10 per cent orange peel powder were recorded higher acceptability as compared to other samples. It is calculated that orange peel powder and Maida can be substituted up to 10 per cent in Maida to prepared orange peel powder without adversely affecting attributes.

Assessment of Climate Adaptability in the Late-Maturing Citrus Industry in Sichuan Province

Sichuan Province is the largest inland area for late-maturing citrus fruit production in China, and its climate conditions are a primary consideration for the cultivation of late-maturing citrus fruits. Based on meteorological data from 2010 to 2020 for the 18 prefecture-level cities and autonomous prefectures in Sichuan Province that cultivate late-maturing citrus fruits, along with the traditional method of dividing the advantages of citrus and the calculation of comparative advantage using factor endowment coefficients, we identified the annual average temperature, annual accumulated temperature ≥ 10 °C, average temperatures in July and January, annual precipitation, and annual sunshine hours as input indicators. We selected the resource endowment coefficient as the output indicator and used the DEA–Malmquist index model to evaluate the climate adaptability of Sichuan’s late-maturing citrus fruit industry. The analysis results indicate that the overall climate conditions in Sichuan are suitable for the growth of late-maturing citrus fruits. However, extensive cultivation of similar varieties has led to a decline in resource endowment across different regions. The use of arable land for cultivating late-maturing citrus fruits has also reduced climate adaptability. Policies that contradict climate adaptability do not support sustainable development within Sichuan’s late-maturing citrus fruit industry.

Morphogenetic characterization of Xanthomonas citri pv. citri and its management

BackgroundPakistan’s economy largely depends on citrus cultivation, and citrus fruits generate significant foreign exchange. Xanthomonas citri pv. citri (Xcc) is the primary cause of citrus canker (CC), which poses a significant threat to the industry. The management of disease is made more difficult by the lack of resistant variants against different Xcc races. Understanding and addressing Xcc are critical for maintaining the industry given the economic reliance on citrus. MethodsIn order to isolate Xcc in a lab, a thorough survey was conducted in the districts of Bahawalpur, Multan, and Dera Ghazi Khan to collect samples showing canker symptoms. Gram-negative bacteria were identified in the isolates by biochemical analysis, and Koch’s postulates confirmed Xcc as the CC causing agent. DNA extraction and sequencing were used in the molecular characterization, which confirmed the phylogenetic relationship with Xcc. Using the disc sensitivity method, nine antibiotics were tested at 300, 500, and 700 ppm concentrations to evaluate CC management. Amoxicillin was found to be highly effective in inhibiting the growth of Xcc colonies. ResultsThe study provided morphogenetic insights and established Xcc as the causal agent of CC. All strains matched Xcc in molecular characterization, but antibiotic sensitivity testing revealed inconsistent efficacy. Amoxicillin proved to be very effective at stopping the growth of Xcc colonies at every tested dosage. ConclusionThis study makes an important contribution to our understanding of XCC and helps the citrus industry develop better disease control plans. Future interventions against citrus canker can benefit greatly from the understanding provided by morphogenetic characterization and antibiotic sensitivity profiles. The discovery of amoxicillin’s high efficacy highlights the drug’s potential for treating diseases linked to Xcc. These results help to protect citrus growing, maintaining the viability of an important industry in Pakistan’s agricultural landscape.

Economic analysis of the biological control in citrus production in Turkey with Green Deal policies

Economic analysis of the biological control in citrus production in Turkey with Green Deal policies

Functional Analysis of RMA3 in Response to Xanthomonas citri subsp. citri Infection in Citron C-05 (Citrus medica)

Citrus bacterial canker disease, caused by Xanthomonas citri subsp. citri (Xcc), poses a significant global threat to the citrus industry. Lateral organ boundaries 1 (Lob1) is confirmed as a citrus susceptibility gene that induces pathogenesis by interaction with the PthA4 effector of Xcc. Citron C-05 (Citrus medica) is a Citrus genotype resistant to Xcc. However, there is little information available on the regulation of Lob1 in resistant genotypes, which is important for the breeding of citrus cultivars resistant to canker disease. This study aimed to identify upstream regulatory factors of Lob1 in Citron C-05 and to investigate its function in disease resistance. ‘Bingtang’ sweet orange (C. sinensis), a susceptible genotype, was utilized as the control. cDNA yeast libraries of Xcc-induced Citron C-05 and ‘Bingtang’ sweet orange were constructed. The capacities of ‘Bingtang’ and Citron C-05 were 1.896 × 107 and 2.154 × 107 CFU, respectively. The inserted fragments ranged from 500 to 2000 bp with a 100% recombination rate. The promoter of Lob1 was segmented into two pieces and the P1 fragment from both genotypes was used to construct a bait yeast (PAbAi-CsLob1-P1; PAbAi-CmLob1-P1). Through library screening with the bait yeast, upstream regulators interacting with the Lob1-P1 promoter were identified and then validated using Y1H and dual-luciferase tests. The expression analysis of the three transcript factors indicated that RMA3 was upregulated by inoculation with Xcc in the resistant Citron C-05, but not in the susceptible sweet orange. The overexpression of CsRMA3 in ‘Bingtang’ sweet orange led to reduced canker symptoms, with a significantly lower pathogen density in the leaves following Xcc inoculation. When CmRMA3 was silenced by virus-induced gene silencing (VIGS) in Citron C-05, typical canker symptoms appeared on the CmRMA3-silenced leaves at 15 days post-inoculation with Xcc. Further expression analyses revealed that the CmRMA3 transcription factor suppressed the expression of Lob1. These results suggest that RMA3 participates in the resistant reaction of Citron C-05 to Xcc infection, and such a response might be in relation to its suppression of the expression of the pathogenic gene Lob1.

Parasitoid guild of the citrus leafminer, Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae) in Tunisian citrus orchards and a new report of Cirrospilus ingenuus Gahan (Hymenoptera: Eulophidae)

A survey of the parasitoid species of the citrus leafminer (CLM), Phyllocnistis citrella Stainton (Lepidoptera: Gracillariidae), a cosmopolitan pest of citrus, was carried out in 2019 and 2020 in the major citrus production area of Tunisia. Four different Eulophidae species were found: Citrostichus phyllocnistoides (Narayanan), representing 81.82% of the identified parasitoids, Semielacher petiolatus (Girault) (9.40%) and the native species Pnigalio pectinicornis (L.) (2.82%). Cirrospilus ingenuus Gahan (Hymenoptera: Eulophidae) is a new report for the parasitoid entomofauna of P. citrella in the country, representing 5.96% of the identified parasitoids. It has probably spread naturally from other Mediterranean regions. Predation by generalist predators is the main mortality factor of CLM (up to 59.11% of the mortality was caused by natural enemies), followed by parasitism (oviposition) (22.47%) and host-feeding (18.42%). Second and third instar larvae of the CLM were the preferred stages for parasitism. Host-feeding and generalist predators’ attacks were most common on first and second instars. Data highlighting the ability for C. phyllocnistoides to develop and disperse clearly predominates in Tunisian citrus orchards. Citrostichus phyllocnistoides may compete with S. petiolatus, exerting a complementary action to that of C. phyllocnistoides, particularly earlier in the season when the densities of the latter species are low. Further studies focusing on inter-specific relationships between these two exotic parasitoids are needed in order to test whether the observed field results could have been estimated from laboratory assays. This will be helpful in critically evaluating the results of the classical biological control programme developed against CLM in Tunisia.

Sublethal and transgenerational effects of broflanilide on the citrus red mite, Panonychus citri.

The citrus red mite, Panonychus citri is a serious pest of the citrus industry and has developed resistance to many acaricides. Broflanilide is a novel meta-diamide insecticide that binds to a new site on the γ -aminobutyric acid receptor with high potency against pests. However, little information has been reported about its effect on the citrus red mite. Broflanilide exhibited higher toxicity to female adults and eggs of a laboratory strain of P. citri The median lethal concentration (LC50), 9.769 mg/L and 4.576 mg/L, respectively) than other commonly used acaricides and was also toxic to two P. citri field strains. Broflanilide treatment with LC10, LC20, and LC30 significantly decreased the fecundity and longevity of female adults of F0 P. citri compared with the control. The duration of larva, protonymph, deutonymph and adult, and total life span in the F1 generation were significantly reduced after treatment of F0 with broflanilide. Population parameters, including the intrinsic rate of increase (r) and finite rate of increase (λ), were significantly increased, and the mean generation time (T) of F1 progeny was significantly reduced in the LC20 treatment. The predicted population size of F1 increased when parental female adults were treated with sublethal concentrations. Broflanilide had high acaricidal activity toward P. citri, and exposure to a sublethal concentration significantly inhibited the population growth of F0. The transgenerational hormesis effect is likely to cause population expansion of F1. More attention should be paid when broflanilide is applied to control P. citri in citrus orchards. © 2024 Society of Chemical Industry.

Digital replica to unveil the impact of growing conditions on orange postharvest quality

The postharvest end-quality of citrus is significantly impacted by pre-harvest factors such as weather, which varies among growing regions. Despite the importance of these factors, the influence of regional weather variations, such as variations in temperature, humidity, wind, vapor pressure deficit (VPD), and solar radiation on postharvest citrus quality, is largely unknown. This study aims to quantify this impact through a physics-driven digital replica of the entire value chain of Valencia oranges, from orchards in South Africa to retail in Europe. Predicted fruit properties data at harvest and hygrothermal sensor data from orchard to retail for different production regions are coupled to a physics-based fruit model to simulate key postharvest fruit quality metrics. These metrics include mass loss, chilling injury, fruit quality index (FQI), remaining shelf life (RSL), total soluble solids (TSS), and titratable acidity (TA). Our digital fruit model reveals that regional weather variability significantly affects fruit quality evolution when comparing data from Nelspruit, Letsitele, and Sunday’s River Valley (SRV). The impact of weather variations is most pronounced in the temperate oceanic climate of SRV compared to the hotter climates of Letsitele and Nelspruit. Our findings indicate that differences in weather conditions between these growing regions impact postharvest mass loss, FQI, RSL, TSS, and TA of Valencia oranges at retail. The impact is up to 10% variation in mass loss and RSL, 4% in TSS, and 1% in TA among oranges grown in different regions. We show that temperature and humidity variations in the postharvest local transport of oranges between different regions largely increase mass loss by up to twofold, FQI by up to ~ 12%, and RSL by up to ~ 15% at retail. Our research also shows that weather temperature is the most important metric during fruit growth affecting various aspects of postharvest orange quality. This study offers valuable insights into the impact of regional weather variations on the quality of oranges available to consumers. These findings could help the citrus industry enhance growing practices, postharvest logistics, retail marketing, and cold chain strategies, thereby improving product quality and consumer satisfaction.

Insecticide Efficacy of Green Synthesis Silver Nanoparticles on Diaphorina citri Kuwayama (Hemiptera: Liviidae).

Diaphorina citri Kuwayama (Hemiptera: Liviidae) is a vector of Liberibacter asiaticus Jagoueix et al. and Liberibacter americanus Teixeira et al., causal agents of the critical yellow dragon disease or Huanglongbing (HLB), which affects citrus production worldwide. Recently, green synthetic nanoparticles have emerged as a potential alternative to control of agricultural insect pests. The insecticide effect of silver nanoparticles (AgNPs) on 2nd instar nymphs of D. citri under laboratory and greenhouse conditions was evaluated. Mortality was recorded 24, 48, and 72 h after application on D. citri nymphs under both laboratory and greenhouse conditions. The laboratory results showed that AgNPs caused 97.84 and 100% mortality at 32 and 64 ppm, respectively, 72 h after treatment. In the greenhouse, AgNPs caused 78.69 and 80.14% mortality using 64 and 128 ppm 72 h after application. This research is the first to evaluate the green synthesis AgNPs on D. citri and are a promising strategy to control the pest.

Chromosome-level genome assembly of the cottony cushion scale Icerya purchasi

The cottony cushion scale, Icerya purchasi, a polyphagous pest, poses a significant threat to the global citrus industry. The hermaphroditic self-fertilization observed in I. purchasi is an exceptionally rare reproductive mode among insects. In this study, we successfully assembled a chromosome-level genome sequence for I. purchasi using PacBio long-reads and the Hi-C technique, resulting in a total size of 1,103.38 Mb and a contig N50 of 12.81 Mb. The genome comprises 14,046 predicted protein-coding genes, with 462,722,633 bp occurrence of repetitive sequences. BUSCO analysis revealed a completeness score of 93.20%. The genome sequence of I. purchasi serves as a crucial resource for comprehending the reproductive modes in insects, with particular emphasis on hermaphroditic self-fertilization.

Biocontrol potential of epiphytic bacteria against Xanthomonas citri pathotypes A and A*

BackgroundCitrus canker caused by the bacterium Xanthomonas citri (Hasse 1915) is known as a dangerous disease that has serious economic impacts on citrus production in many tropical and subtropical countries. In Iran, Citrus canker disease has caused significant damage to various citrus fruits, particularly limes. Nowadays, employing antagonistic bacteria as an effective and environmentally friendly method for plant disease management has gained special importance.ResultsCitrus leaf samples were collected from different regions of Iran, and after isolating epiphytic bacteria, ex planta and in planta investigations concerning antagonistic activities of the isolates against Xanthomonas citri pathotypes A and A* were performed. A total of 94 epiphytic bacterial isolates were isolated from citrus aerial parts. Based on biochemical, physiological, morphological, and genotypic tests, it was determined that these bacteria belong to the Bacillus and Staphylococcus genera. The highest inhibition activity against the pathogenic bacterium was related to isolates D4 and D5. Using the molecular method and the resulting dendrogram, it was found that these isolates were most similar to Bacillus amyloliquefaciens. The present findings demonstrated that pathogenicity test on key lime leaves infected with X. citri pathotypes A and A*, along with the application of the biocontrol strain B. amyloliquefaciens, resulted in a significant reduction in the number of canker lesions.ConclusionThe results strongly suggested that the identified antagonistic bacterial isolates hold promising potential as biocontrol agents for managing citrus bacterial canker disease.

Citrus-mediated gene silencing of cytochrome P450 suppresses insecticide resistance and increases mortality in Diaphorina citri.

Asian citrus psyllid, Diaphorina citri, is a hemipteran that vectors the causal pathogen of citrus greening disease, or huanglongbing (HLB). HLB is a tree killing disease that has severely limited citrus production globally. Unfortunately, there is no cure for this disease, and mitigation depends on multiple insecticide applications to reduce vector populations. Silencing of cytochrome P450 expression associated with detoxification enzymes by RNA interference is known to increase susceptibility of D. citri to insecticides. However, dsRNA was previously introduced into psyllids by topical applications. The possible application of this technology for pest management will require effective field delivery of the dsRNA. Therefore, we evaluated a virus vector (Citrus tristeza virus; 'mild strain' T36) to deliver gene silencing directly to this sap-sucking insect via plant phloem. Citrus macrophylla plants inoculated with CTV expressing a truncated consensus sequence of CYP450 (CTV-tCYP450) constantly produced small interfering RNA in the plant phloem that targeted five cytochrome p540 (CYP450) genes in D. citri. Insecticide susceptible D. citri reared on citrus infected with CTV-tCYP450 were subsequently more susceptible to imidacloprid, fenpropathrin, carbaryl, and chlorpyrifos than those reared on citrus infected with wildtype CTV or non-infected negative controls. Additionally, nymph survival and adult lifespan were significantly reduced when psyllids were reared on CTV-tCYP450 citrus plants compared with controls. Interestingly, similar results were obtained after one and two generations of rearing. Finally, field-collected psyllids from areas with known broad-spectrum insecticide resistance were rendered more susceptible to imidacloprid and fenpropathrin after feeding on CTV-tCYP450 citrus trees as compared with those reared on controls. The integration of citrus-mediated RNA inference targeting psyllid detoxification enzymes could function as a resistance management tool and reduce insecticide input in an integrated pest management program for HLB. © 2024 Society of Chemical Industry.

Forecasting the Expansion of Bactrocera tsuneonis (Miyake) (Diptera: Tephritidae) in China Using the MaxEnt Model.

The invasive pest, Bactrocera tsuneonis (Miyake), has become a significant threat to China's citrus industry. Predicting the area of potentially suitable habitats for B. tsuneonis is essential for optimizing pest control strategies that mitigate its impact on the citrus industry. Here, existing distribution data for B. tsuneonis, as well as current climate data and projections for four future periods (2021-2040, 2041-2060, 2061-2080, and 2081-2100) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) were obtained. The distribution of B. tsuneonis under current and different climate change scenarios in China was predicted using the optimized MaxEnt model, ArcGIS, and the ENMeval data package. Model accuracy was assessed using ROC curves, and the primary environmental factors influencing the distribution of the pest were identified based on the percent contribution. When the regularization multiplier (RM) was set to 1.5 and the feature combination (FC) was set to LQH, a model with lower complexity was obtained. Under these parameter settings, the mean training AUC was 0.9916, and the mean testing AUC was 0.9854, indicating high predictive performance. The most influential environmental variables limiting the distribution of B. tsuneonis were the Precipitation of Warmest Quarter (Bio18) and Temperature Seasonality (standard deviation ×100) (Bio4). Under current climatic conditions, potentially suitable habitat for B. tsuneonis in China covered an area of 215.9 × 104 km2, accounting for 22.49% of the country's land area. Potentially suitable habitat was primarily concentrated in Central China, South China, and East China. However, under future climatic projections, the area of suitable habitat for B. tsuneonis exhibited varying degrees of expansion. Furthermore, the centroid of the total suitable habitat for this pest gradually shifted westward and northward. These findings suggest that B. tsuneonis will spread to northern and western regions of China under future climate changes. The results of our study indicate that climate change will have a major effect on the invasion of B. tsuneonis and have implications for the development of strategies to control the spread of B. tsuneonis in China.

English

The district Toba Tek Singh is located in the center of Punjab province. It occupies 2nd important position in national citrus production after Sargodha, with citrus orchard area of 11412 hectares and annual production of 160758 tons. Citrus productivity in Pakistan, in general, and Toba Tek Singh, in particular, is far below its its potential which could be attributed to several factors but poor soil health and inadequate soil fertility may be considered an important reason. A comprehensive nutrient indexing survey of thirty citrus orchards grown in different parts of district Toba Tek Singh was conducted to evaluate the soil characteristics and plant nutrient status. GPS coordinates of selected sites were recorded prior to sampling. Soil samples were collected at 0-20 cm, 21-40 cm and 41-60 cm depth using standard procedure. Five soil samples were collected from each site to get a composite sample for each depth. The leaf samples were collected from the 7-month-old non-fruiting branches of plants around the tree canopy during the month of September, 2022. Five healthy and uniform citrus trees were sampled from each site to get a composite leaf sample. The soil samples were analyzed for pH, electrical conductivity (EC), soil organic matter (SOM) and calcium carbonate (CaCO3). The soil and leaf samples were analyzed for macro and micronutrients. It was found that most of orchard soils of district Toba Tek Singh were moderately alkaline (pH 7.52-8.90), slight to strong calcareous (2-15% CaCO3), non-saline (0.77-3.0 dS m-1 EC) and low in SOM (0.23-1.49%) with low to medium nitrogen (0.01-0.06%) and phosphorus (0.58-10.52 mg kg-1) while medium to high potassium (56.47-315.34 mg kg-1). The sampled soils were low to marginal in boron (0.09-0.72 mg kg-1), copper (0.05-0.59 mg kg-1), iron (0.23-10.75 mg kg-1) and zinc (0.03-1.83 mg kg-1) while adequate in manganese (1.35-26.20 mg kg-1). Leaf analysis revealed that almost 50% orchards were deficient in phosphorus (0.05-0.23%) and potassium (0.40-1.76%), while having low to marginal values of copper (1.96-20.99 mg kg-1), zinc (4.13-31.96 mg kg-1), boron (3.12-95.40 mg kg-1), manganese (42.62-96.46 mg kg-1) but adequate iron (171-552 mg kg-1). The surveyed orchard soils were mostly alkaline calcareous, deficient in organic matter and having low to moderate macro and micronutrients.

Farmers’ perceptions and management of citrus fungal diseases in Benin

Background and aimCitrus production represents an important activity for the national economy and a source of income for farmers in Benin. However, fungal diseases are a major constraint to production intensification. The aim of this study is to assess farmers’ perceptions on citrus fungal diseases in production areas in Benin. MethodsA survey was conducted among 417 farmers between July and December 2021 in four major citrus-producing agro-ecological zones (zones V, VI, VII and VIII) to collect their perceptions, knowledge and management practices of citrus fungal diseases. ResultsFarmers reported that fungal diseases are one of the main constraints to citrus production, including black spot, anthracnose, brown rot, sooty mold and fruit rot. Among them, black spot disease is the most severe, causing damage to production. According to farmers, symptoms appear on fruit after fruit set, with a very remarkable presence and high incidence at maturity. Although farmers are most of times aware of the damage caused by fungal diseases with adverse consequences on their income, they have a poor knowledge of appropriate phytosanitary products to manage these diseases. Indeed, the majority of farmers (>60 %) use chemical insecticides, which they reported to be ineffective against citrus fungal diseases. Although chemical insecticides are their only recourse, almost 40 % use nothing to control these diseases. Farmers stated that climatic variability is a factor favoring the development of diseases, leading to reduced production. ConclusionsAmong the several citrus fungal diseases, black spot is perceived as the most damaging, causing greater yield losses under favorable conditions, coupled with an almost total absence of appropriate control methods. This study contributes to the reorganization of the citrus industry and to decision-making on capacity building for farmers in terms of orchard pest protection, in order to guarantee better production of marketable and exportable fruit.

Effect of climate change of the quality of Citrus fruit produced in South Africa

Climate change is an observed reality with a significant impact globally. South Africa is not immune to this phenomenon. Like the rest of the world, South Africa experiences rise in mean air temperature and changes in rainfall trends. Since plant systems are influenced by weather, it is expected that climate change will have an effect on the production and quality of fruit. The objective of this study was to determine the impact of climate change on the quality of citrus fruit produced in South Africa. In conducting the study, historical fruit quality data was collected from packhouses in the Eastern and Western Cape provinces of South Africa over a period of 12 and 8 years respectively. Trend analysis was done on the data to determine whether there is a trend that can be observed over the period of data collection. The total soluble solids of fruit showed a marginal increase over the period of observation. Titratable acidity showed a marginal decrease. The incidence of sunburn on fruit seemed to increase over time. Other disorders like decay, creasing and oleocellosis did not show a definite trend of increasing or decreasing over time. Rind disorders seemed to decrease during the period of observation. This report discusses how the observed trends were influenced by changes in rainfall and temperature over the period of observation. It is then concluded that in this case study, the impact of climate change was not very profound and it had both negative and positive effects. The current results point toward a bleak future for citrus producers. To remain profitable, it may be necessary for producers to invest in climate change adaptation technologies. Key words: Climate change, citrus fruit, fruit quality, oleocellosis, titratable acidity

Rootstocks for the Mediterranean citrus industry: current choices and new releases

Modern citriculture relies on the use of rootstocks to guarantee adaptability to environmental and biotic constraints and to speed up the establishment of a potentially unlimited number of homogeneous plants of a specific clone, which in turn ensures uniformity in the production of high-quality fruit. In this contribution, the status of rootstock availability for the Mediterranean citrus industry is described along with its evolution during the last decades. The major turning points in rootstock choice were caused by the spread of new diseases, such as Citrus Tristeza Virus (CTV), that hastened the use of resistant or tolerant rootstocks. In Italy, the growers decisions on rootstock replacement were facilitated by information from rootstock trials performed for more than 70 years in several areas of southern Italy, as well as information from other countries. However, there is still the need to find alternatives to sour orange (which was the most commonly used rootstock before the CTV outbreak), especially for cultivation under suboptimal growing conditions. Nowadays, the process of replacing standard rootstocks with new ones with better performance should be assisted by a long-term evaluation strategy, since negative characteristics can become evident after many years of evaluation in combination with specific scion varieties. Ongoing rootstock breeding programs in different parts of the world and in Italy are critically described.

The wall-associated receptor-like kinase CsWAKL01, positively regulated by the transcription factor CsWRKY53, confers resistance to citrus bacterial canker via regulation of phytohormone signaling.

Citrus bacterial canker (CBC) is a disease that poses a major threat to global citrus production and is caused by infection with Xanthomonas citri subsp. citri (Xcc). Wall-associated receptor-like kinase (WAKL) proteins play an important role in shaping plant resistance to various bacterial and fungal pathogens. In a previous report, CsWAKL01 was identified as a candidate Xcc-inducible gene found to be up-regulated in CBC-resistant citrus plants. However, the functional role of CsWAKL01 and the mechanisms whereby it may influence resistance to CBC have yet to be clarified. Here, CsWAKL01 was found to localize to the plasma membrane, and the overexpression of the corresponding gene in transgenic sweet oranges resulted in pronounced enhancement of CBC resistance, whereas its knockdown had the opposite effect. Mechanistically, the effect of CsWAKL01 was linked to its ability to reprogram jasmonic acid, salicylic acid, and abscisic acid signaling activity. CsWRKY53 was further identified as a transcription factor capable of directly binding to the CsWAKL01 promoter and inducing its transcriptional up-regulation. CsWRKY53 silencing conferred greater CBC susceptibility to infected plants. Overall, these data support a model wherein CsWRKY53 functions as a positive regulator of CsWAKL01 to enhance resistance to CBC via the reprogramming of phytohormone signaling. Together these results offer new insights into the mechanisms whereby WAKLs shape phytopathogen resistance while underscoring the potential value of targeting the CsWRKY53-CsWAKL01 axis when seeking to breed CBC-resistant citrus plant varieties.