Citrus-growing Areas Research Articles

Population structure, spatial aggregation, and sampling plan for the Texas citrus mite, Eutetranychus banksi (Acari: Tetranychidae) on citrus.

Eutetranychus banksi (McGregor) (Acari: Tetranychidae) is an invasive spider mite native to the Americas. In 2013 it invaded the main citrus-growing area in Spain producing significant damage and requiring chemical treatments. This work examines its population structure, spatial distribution and presents a sampling plan, which will assist in developing an integrated pest management (IPM) strategy. There were differences in the population structure on fruits and leaves, as well as between leaves from different flushes with fluctuations over time correlated with variations in sex ratio. No differences in aggregation at the different plant strata were found; however, immature stages showed a higher aggregation than adults, with females being the sex with the lowest aggregation. There was a high correlation between E. banksi motile forms and adult females with the total population, thus both were used as reference stages to develop sampling plans. We recommend binomial sampling of 100 leaves for female monitoring, sampling two leaves per tree on 25 trees per transect regularly spaced along two diagonal transects, the first oriented northeast to southwest and the second northwest to southeast. To be more accurate, it is possible to survey the presence/absence of motile forms. In this case, four leaves per tree in 50 trees per transect should be monitored. This study has resulted in the first sampling plan for E. banksi, one of the most damaging citrus mite species described so far. The binomial sampling plan involves monitoring reference developmental stages, as well as a reasonable sample size that makes it applicable in field sampling for decisions making based on a future intervention threshold. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Impact of Phytophthora Spp. on Morphological, Physical, and Biochemical Parameters of Citrus reticulata

Citrus gummosis, caused by Phytophthora spp., is one of the economically critical fungal diseases prevailing in the major citrus-growing areas of the country. The fungus induces alterations in morphological and physiological parameters (leaf area, fruit weight, fruit volume, fruit length, fruit diameter, peel thickness, peel weight, rag weight, and juice weight). Therefore, the study was conducted to analyze the physical and biochemical parameters of citrus plants of various Citrus reticulata infected with phytophthora gummosis. Citrus leaves and fruits were collected to determine different morphological, physical, and biochemical parameters to compare the diseased and healthy citrus samples. There was a significant difference (P 0.05) in physical parameters between infected and healthy citrus samples. The fruit size was significantly lower within the range of 29.1-35.4 cm2 in the diseased plants as compared to healthy ones (37.3-43.6 cm2). The fruit volume of infected samples, with a maximum difference of 37.1 cm3, was also recorded in infected and healthy samples. The infected citrus samples had lower fruit weights of 111.3–145.2 g than the healthy samples (147.8–175.9 g). The leaf area was significantly less for diseased plants (11.8–20.0 cm2) compared to 17.1-29.5 cm2 for healthy samples. Other physical parameters were also altered, but not significantly. Similarly, biochemical parameters such as TSS to Acid ratio 77.9–86.8, Total Soluble Solids 11.3–11.6%, Vitamin C 55.4–77.9 mg/100 mL, total phenolic contents 288.8–341.9, total flavonoids 210.1–240.2, antioxidant activity 655.7–749.5, and pH 3.13–3.32 were found to be significantly lowered at P 0.05 in diseased citrus samples as compared to those in healthy citrus samples with the mean values of 101.3–109.5, 12.2–12.4%, 91.5–123.5 mg/100 mL, 3636.1-421.2, 249.7–285.6, 749.6–867.7, and 3.52–3.81, respectively. The findings of the research revealed the devastating impact of Phytophthora spp. on C. reticulata, resulting in low yield and fruit quality.

Geographic Location, Population Dynamics, and Fruit Damage of an Invasive Citrus Mealybug: The Case of Delottococcus aberiae De Lotto in Eastern Spain.

The invasive mealybug Delottococcus aberiae De Lotto (Hemiptera: Pseudococcidae) has rapidly spread in the Mediterranean basin since its detection in 2009 in the Valencia Community in eastern Spain. The use of sticky traps baited with its sex pheromone, (4,5,5-trimethyl-3-methylenecyclopent-1-en-1-yl)methyl acetate, has allowed to determine the geographical distribution of D. aberiae by means of the surveillance network described in the present work. The population monitoring of the pest over a five-year period (2019-2023) has revealed an increase from 31% to 70% of the affected citrus-growing area. The monitoring network has also allowed a better understanding of the pests' biological cycle throughout the year. The populations start growing from March to June and reach their maximum in July-August. During autumn, there is a gradual decline in the population. Although the highest annual populations were detected in 2022 and 2023, the greatest crop losses were recorded in 2020 and 2021, with mean values near 18%. Data suggest that the damage responsible for fruit deformation, and thus the economic losses, are related to the population levels in spring (April-May) rather than those in summer (July-August). The findings of this study can be valuable for future research and development of effective pest control strategies.

Biological and molecular characterization of citrus bent leaf viroid

Background and aimCitrus bent leaf viroid (CBLVd) is one of the emerging and widely distributed viroids in citrus-growing areas of the world, including Pakistan. Previously, CBLVd has been reported in Pakistan for the first time in 2009. Therefore, characterization of CBLVd is required to monitor the viroid status in the citrus orchards concerning citrus decline. MethodsBiological and molecular characterization of CBLVd was studied through biological indexing and confirmation through RT-PCR, followed by phylogenetic analysis of selected CBLVd isolates. Among four citrus cultivars viz., Kinnow (Citrus nobilis × Citrus deliciosa), Mosambi (C. sinensis), Futrell's Early (C. reticulata) and Lemon (C. medica) used as indicator plants for two transmission trials viz., graft inoculation and mechanical inoculation. Graft inoculation was more efficient than mechanical inoculation. ResultsSymptoms such as mild mosaic, slight backward leaf bending, and leaf curling were observed after eight months’ post-inoculation. Citrus nobilis × Citrus deliciosa, C. reticulata and C. sinensis were more sensitive to CBLVd as compared to C. medica. Inoculated plants were reconfirmed through RT-PCR amplicons of 233 bp. The phylogenetic tree of submitted sequences showed more than 90% relevance of CBLVd in Pakistan compared to the rest of the world. ConclusionsThere was slight genetic variability, but more than 90% relevance was found among the submitted and already reported CBLVd isolate from Pakistan. Scanty literature is available regarding the biological and molecular studies of CBLVd in Pakistan. Therefore, the transmission and molecular characterization of CBLVd in Pakistan were studied for the first time.

SUITABILITY AREAS FOR Candidatus Liberibacter asiaticus UNDER DIFFERENT CLIMATE CHANGE SCENARIOS IN MEXICO

<p><strong>Background.</strong> Climate change models have projected an increase in the distribution of certain crop pests of economic importance by forecasting more favorable future conditions for these organisms. In citrus farming, Huanglongbing is one of the most devastating diseases worldwide, since it has caused the death of millions of trees. <strong>Objetive.</strong> The objective of this study was to estimate the current and future distribution of <em>Candidatus </em>Liberibacter asiaticus in Mexico, under the climate change scenarios SSP2 4.5 and SSP5 8.5, for the years 2050 and 2070. <strong>Methodology.</strong> Distribution models were generated with MaxEnt and R, using uncorrelated bioclimatic variables from eight General Circulation Models (GCM) derived from CMIP6 and disease presence data. <strong>Results.</strong> The results indicate that the current suitability is 44.6 %. The future distribution depended on how model predictions were pooled. An optimistic approach that considered the intersection of all models showed a small reduction of 4.1% while, considering the union of all the GCM models, the increase will vary from 12.3 to 20.1 % of the Mexican territory depending on the particular scenario and time projection. <strong>Implications.</strong> The zones of potential occurrence of <em>Candidatus </em>Liberibacter asiaticus include most of the citrus-growing areas in Mexico. <strong>Conclusion. </strong>In some regions, future scenarios show a reduction in the potential occurrence of the species in citrus plantations. However, the risk remains because its surroundings include suitable areas that can be sources of dissemination of the disease. </p>

Risk-based regionalization approach for area-wide management of HLB vectors in the Mediterranean Basin.

Huanglongbing (HLB) is one of the most devastating citrus diseases worldwide. It is associated with the non-culture bacteria Candidatus Liberibacter spp., which can be transmitted by grafting and/or the psyllid vectors Diaphorina citri (ACP) and Trioza erytreae (AfCP). Although HLB has not been reported in the Mediterranean Basin to date, both vectors are present, and thus represent a serious threat to the citrus industry in this region. Resistant citrus cultivars or effective therapeutic treatments are not currently available for HLB. Nevertheless, area-wide pest management via coordinated management efforts over large areas has been implemented in Brazil, China and the USA for HLB control. This study proposes an open access flexible methodology to address area-wide management of both HLB vectors in the Mediterranean Basin. Based on a risk-based approach which considers climatic information and other variables that may influence vector introduction and spread, such as conventional, organic, abandoned and residential citrus areas as well as transportation corridors, an area-wide management division in pest management areas (PMAs) is proposed. The size and location of these PMAs were estimated by means of a hierarchical clustering algorithm with spatial constraints whose performance was assessed under different configuration scenarios. This proposal may assist policymakers and the citrus industry of the citrus-growing areas of the Mediterranean Basin in risk management planning in the case of the spread of HLB vectors or a possible introduction of the disease. Additionally, it may be a valuable resource to inform opinion dynamic models, enabling the identification of pivotal factors for the success of control measures.

Risk assessment of Resseliella citrifrugis for the EU.

Following a request from the European Commission, the EFSA Panel on Plant Health performed a risk assessment of the citrus fruit midge Resseliella citrifrugis (Diptera: Cecidomyiidae), an oligophagous species, which feeds on fruits of Citrus spp., and is reported from China. The pest was temporarily regulated in October 2022 (Regulation (EU) 2022/1941, under Art. 30 (2016/2031)). The entry risk assessment focused on the citrus fruit pathway. Three scenarios were considered: A0 (current practice, i.e. regulated pest for the EU), A1 (deregulation) and A2 (A0 with additional stand-alone post-harvest cold treatment). Based on the outputs of the entry model, under scenario A0, slightly less than 40 potential founder populations per year are expected (median; 90%-uncertainty interval between about one per 30 years and about 3,000 per year). Under scenario A1, the risk of entry increases by about three times and reaches about 120 potential founder populations per year (median; 90%-uncertainty interval between about one per 10 years and about 9,000 per year). Compared to scenario A0, the risk of entry is orders of magnitude lower for scenario A2 (median = about one potential founder population per 120 years; 90%-uncertainty interval between one per about 600 million years and about two per year). The main uncertainties in the entry assessment are the probability of transfer, the RRO effectiveness (for scenario A2) and the disaggregation of consignments (transport of citrus fruit in boxes or lots to different locations). For all scenarios, the number of established populations is only slightly lower than the number of potential founder populations. Establishment is thus not expected to be a major constraint for this pest to then spread and cause impacts, despite the uncertainty about the pest thermal requirements. The median lag period between establishment and spread is estimated to be about 18 months (90%-uncertainty interval between about 7 and 54 months). After the lag period, the median rate of spread by flying and due to transport of harvested citrus fruit from orchards to packinghouses is estimated at about 100 km/year (90%-range between about 40 and 500 km/year). The main uncertainties in the spread assessment include the level of susceptibility of cultivars of different citrus species in the EU, the spread rate in China and the climate suitability of the initial spread focus in the EU. The median impact of R. citrifrugis in the EU citrus-growing area (proportion of infested citrus fruit out of harvested citrus fruit) is estimated at about 10% (90%-uncertainty interval between about 2% and 25%). Uncertainties affecting the impact assessment include the susceptibility of different citrus cultivars and the effect of the citrus fruit-harvesting season in the EU (mainly winter, the less suitable season for the pest).

Species distribution models predicting climate suitability for the psyllid Trioza erytreae, vector of citrus greening disease

The African citrus psyllid, Trioza erytreae (Hemiptera: Triozidae), is a vector of citrus greening (Huanglonbing - HLB), a bacterial citrus disease caused by Candidatus liberibacter spp. Native to Africa, T. erytreae was detected in the Canary Islands and Madeira in the early 2000s and then in northwestern Spain in 2014. Since then, T. erytreae has become established along the Atlantic coastal areas of the Iberian Peninsula. Therefore, an accurate assessment of the potential long-term establishment of T. erytreae in major citrus-growing regions of Europe and the world is urgently needed to design adapted control strategies. I calibrated correlative species distribution models to understand the bioclimatic characteristics that determine the distribution of T. erytreae, and to assess the climatic suitability of the world's major citrus-growing regions for the psyllid under current and future climate conditions. I calibrated the models using only distribution data from Africa (its native range), the Canary Islands, and Madeira, and evaluated them using available data from the invaded area in continental Europe. This approach aims to avoid spurious good measures of model accuracy arising from spatial autocorrelation between the calibration and evaluation datasets. The models identify mild summer and winter temperatures and high levels of precipitation as optimal conditions for long-term psyllid establishment, consistent with its physiology. In Europe, models predict only the Atlantic coastal regions of the Iberian Peninsula as highly climatically suitable, a spatial pattern that corresponds exactly to the area currently invaded by the psyllid. Models predict that most of the important citrus-growing areas in the world are, and will remain in the future, poorly adapted to T. erytreae except in case of future physiological adjustments. These results are crucial for the design of appropriate pest management strategies and are timely for Europe where the African citrus psyllid has recently been detected.

Comparison of Serological and Molecular Methods for Detection of Spiroplasma citri in Moroccan Citrus-Growing Areas.

Spiroplasma citri, a helical motile, wall-less, and cultivable microorganism of the class Mollicutes, is the agent of the citrus stubborn disease. There is currently a lack of data about the presence of this pathogen in Moroccan citrus orchards. This study aims to validate serological and molecular methods for routine S. citri diagnosis in Moroccan citrus groves. To provide an update on the present status of the outbreak of the pathogen in Moroccan citrus orchards, a survey of S. citri was conducted in the main citrus-growing regions of Morocco. A total of 575 leaf samples were collected from citrus trees with symptoms attributable to S. citri infection. Samples were collected during 2020 and 2021 from 23 citrus orchards. The presence of S. citri was tested in all samples using the double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA). Using this method, 57 samples were found to be infected with S. citri, 41 samples had doubtful results, and the remaining samples were negative. To corroborate the results of the DAS-ELISA test, 148 samples were chosen for additional molecular testing using conventional polymerase chain reaction (PCR) and real-time PCR (qPCR) based on specific primer pairs targeting three different genes (putative adhesion-like gene P58, putative adhesion gene P89, and spiralin gene). Using primers that target the putative adhesion-like gene P58, S. citri was detected by conventional and real-time PCR amplification from plant tissue with differing degrees of specificity. The results allowed us to determine the incidence of S. citri in all Moroccan citrus orchards, with a wide range of positive samples varying from 6.5% to 78%, and to show that molecular tests, particularly real-time PCR assays that target the putative adhesion-like gene P58, are the most sensitive for making an accurate diagnosis of S. citri. Indeed, the real-time PCR with P58-targeting primers yielded positive results from all positive and doubtful ELISA samples as well as some negative samples, with an OD value close to 1.5× times healthy samples, thus demonstrating a high sensibility of this technique.

Risk assessment of Citripestis sagittiferella for the EU.

Following a request from the European Commission, the EFSA Panel on Plant Health performed a risk assessment of Citripestis sagittiferella (Lepidoptera: Pyralidae), the citrus pulp borer, an oligophagous pest reported from South-East Asia and restricted to Citrus spp. The entry risk assessment focused on the citrus fruit pathway. Two scenarios were considered: scenario A0 (current practice) and A2 (additional post-harvest cold treatment). Based on the outputs of the entry model obtained in scenario A0, the median number of founder populations in the EU citrus-growing area is estimated to be slightly less than 10 per year (90%-uncertainty interval between about one entry per 180 years and 1,300 entries per year). The risk of entry and the simulated numbers of founder populations are orders of magnitude lower for scenario A2 compared to scenario A0. The key uncertainties in the entry model include transfer, the cold treatment effectiveness, the disaggregation factor and sorting. The simulated numbers of established populations are only slightly lower than the numbers of founder populations. As the probability of establishment has little impact on the number of established populations, it is not a major source of uncertainty, despite the lack of data on the thermal biology of the pest. The median lag period between establishment and spread is estimated to be slightly more than 1 year (90%-uncertainty interval between about 2months and 33months). After the lag period, the median spread rate by natural means (flying) and due to transport of harvested citrus fruit from orchards to packinghouses is estimated at about 100km/year (90%-uncertainty interval between about 40 and 500km/year). The main sources of uncertainties affecting the spread rate include the extent to which environmental factors could hamper the build-up of the populations and the lack of data on the spread rate at the origin. The median impact of C. sagittiferella in the EU citrus-growing area is estimated at about 10% of infested fruits among the harvested citrus fruits (90%-uncertainty interval between about 2% and 25%). Uncertainties affecting the impact assessment include the susceptibility of different Citrus species and cultivars.

First report of citrus black spot disease caused by Phyllosticta citricarpa in Benin

In Benin, citrus production represents an important activity in the national economy and source of income for farmers. For a decade, the majority of orange orchards in Benin have been affected by a disease that is expressed by the appearance of spots on the fruits (Lokossou et al., 2009). A preliminary study conducted on farmers’ perception on the presence of this disease revealed positive answers from all 417 interviewed orchardists. In July 2021, 15 orchards were randomly selected for inspection in four orange production districts in Benin: Djidja (7°20’N, 1°56’E), Zakpota (7°15’N, 2°11’E), Lalo (6°56’N, 1°56’E) and Bopa (6°35’N, 1°57’E). Between 50 to 100% of the trees in the inspected orchards were affected by the disease. Disease symptoms consisted of numerous tiny to middle-sized dark brown to black spots, ranging in size from 3 to 10 mm in diameter. The tiny spots had a grey centre with a dark brown to black border surrounded by a green or yellow halo, depending on the maturity of the fruit. In cases of severe infection, the fruits were completely covered with black spots, and rot (Fig. 1). The leaves also had numerous black spots. In cases of less severe infection, symptoms were limited to the fruits. Four fruits per orchard, in total sixty fruits, showing black spots were randomly selected each of the inspected orchards. A fungus was isolated from the diseased orange fruits on potato dextrose agar medium. The fungus was identified as Phyllosticta citricarpa based on morphological and cultural characteristics. The fungus produced a slow mycelial growth with irregular edged colonies surrounded by a larger translucent zone of immersed clear mycelium (Fig. 2). The centre of the colonies was composed of grey aerial mycelium forming a plectenchymatous rind. The reverse had a very dark centre surrounded by grey and beige areas. Hard, black mass stromas appeared after seven to eight days and ripe pycnidia containing conidia after 10 to 14 days (Fig. 3). Conidia were 9.4 - 12.7 μm long and 5.0 - 8.5 μm wide, ellipsoid to obovoid with atruncate base, hyaline, guttulate, aseptate with a tiny apical mucoid and translucent layer appendage, 3–10 μm long and 1.5 μm wide (Fig. 4). These morphological features confirm the identity of the fungus as Phyllosticta citricarpa (Baayen et al., 2002). Koch's postulates were performed in the laboratory on 30 healthy ripe orange fruits, with two replicates, by injecting 5 μl of a suspension of 106 conidia/ml with a sterile medical needle approximately 2 mm deep in the albedo of fruit. On each fruit, 12 points were inoculated. Control fruits were inoculated with sterile needle and distilled water. Inoculated fruits were kept at room temperature (25 ±2°C). After 15 days, the inoculated fruits developed similar symptoms to those observed in the orange orchards while no symptoms were observed on the untreated fruits (Fig. 5). Phyllosticta citricarpa, was re-isolated from lesions developed on inoculated fruit. Phyllosticta citricarpa (syn. Guignardia citricarpa) has been found previously in Australia, in tropical and subtropical citrus-growing areas of Africa (Angola, Ghana, Kenya, Mozambique, Tunisia, Uganda, Namibia, South Africa, Zambia, Zimbabwe), the Americas (Brazil, Florida), and in Asia (China, India) (EFSA et al., 2020). This is the first report of Phyllosticta citricarpa causing citrus black spot in Benin. Management methods and strategies are being developed to control and limit the spread of the disease in the country. The authors thank the Partnership for Skills in Applied Sciences, Engineering and Technology (PASET) and Regional Scholarship and Innovation Funds (RSIF) programme, the Université Félix Houphouët-Boigny of Côte d'Ivoire, the Institut National des Recherches Agricoles du Bénin (INRAB), the African Centre of Excellence for Climate Change, Biodiversity and Sustainable Agriculture (CEA-CCBAD/Côte d'Ivoire) and the Laboratoire de Phytopathologie du Centre National de Spécialisation en Fruits et Légumes (CNS-FL) /INERA/Burkina-Faso for financial and technical support.

Citrus Tristeza Virus: From Pathogen to Panacea.

Citrus tristeza virus (CTV) is the most destructive viral pathogen of citrus. During the past century, CTV induced grave epidemics in citrus-growing areas worldwide that have resulted in a loss of more than 100 million trees. At present, the virus continues to threaten citrus production in many different countries. Research on CTV is accompanied by distinctive challenges stemming from the large size of its RNA genome, the narrow host range limited to slow-growing Citrus species and relatives, and the complexity of CTV populations. Despite these hurdles, remarkable progress has been made in understanding the CTV-host interactions and in converting the virus into a tool for crop protection and improvement. This review focuses on recent advances that have shed light on the mechanisms underlying CTV infection. Understanding these mechanisms is pivotal for the development of means to control CTV diseases and, ultimately, turn this virus into an ally.

Citrus Irrigation With Desalinated Seawater Under a Climate Change Scenario.

In arid and semiarid regions, the current lack of natural water resources is driving the use of alternative sources for crop irrigation, such as desalinated seawater (DSW). However, the use of DSW could affect the crop productivity due to its chemical composition (predominance of phytotoxic ions: Na+, Cl−, and B). Citrus species are classified as salt and boron-sensitive; however, the rootstock plays a fundamental role in the tree’s tolerance of abiotic stresses. One-year-old ‘Verna’ lemon trees grafted on two rootstocks (CM, Citrus macrophylla, and SO, sour orange) were used. These rootstocks differ in their salinity and boron tolerance, SO being more tolerant than CM. The experiment was carried out at high temperature (35/27°C), and the plants were irrigated with three types of water supplemented with Hoagland nutrients: DSW, DLB (DSW with low boron), and Control (distilled water). The plants were irrigated three times per week and harvested 7 months after the treatments started. The response to high levels of Cl−, Na+, and B was rootstock-dependent. Under the high temperature conditions, the growth of plants grafted on SO was not affected by DSW, and these plants did not reach the Cl− threshold of phytotoxicity, so the decrease in the shoot growth of plants grafted on CM due to DSW irrigation was related more to Cl− rather than the foliar Na+ accumulation. Plants grafted on SO and irrigated with DSW accumulated more B than those grafted on CM, surpassing the threshold of phytotoxicity and producing greater oxidative stress. As the growth of these plants was not reduced, the effects of DSW on plant growth were not directly related to the concentration of B and there must be some mechanisms that allow these plants to withstand the negative effects of high foliar B, such as the increased levels of quaternary ammonium compounds. Since the response of citrus plants to DSW depended on the rootstock, the results obtained in this experiment, using DSW at high temperature, could be useful for the future management of citrus crops, because climate change will increase temperatures and exacerbate the scarcity of water resources in citrus-growing areas.

Grafting improves tolerance to combined drought and heat stresses by modifying metabolism in citrus scion

Mediterranean basin and other citrus-growing areas, such as Florida or California, are among the most vulnerable regions to the impacts of global warming. Therefore, citrus will be likely subjected to increasing periods of water scarcity combined with high temperatures that will impair plant growth, development and yield. In citrus industry, grafting is used to improve varietal characteristics, such as abiotic stress tolerance. Previous research showed that under drought and heat stress conditions, Carrizo citrange ( Poncirus trifoliata × Citrus sinensis ) is a better rootstock than Cleopatra mandarin ( Citrus reshni ) because it induces a higher antioxidant activity on the scion, reducing oxidative damage and increasing plant tolerance. Here, it is shown that metabolic reconfiguration, including changes in carbohydrate and amino acid fluxes, are key responses for plant acclimation to stress conditions. Moreover, the importance of the rootstock on scion metabolic and hormonal responses to drought and heat stress combination has been addressed by using reciprocal grafting between Carrizo and Cleopatra genotypes. Thus, Carrizo as a rootstock improves the metabolic and hormonal response of Cleopatra scions to the stress combination by inducing the accumulation of protective compounds such as raffinose, galactinol and salicylic acid. In turn, Cleopatra as a rootstock reduces levels of raffinose, galactinol, proline, phenylalanine and tryptophan in Carrizo scions, which impairs plant tolerance to the stress combination. Our findings show the effect of the rootstock on scion metabolic response to stress combination and remark the importance of the rootstock in citrus plants exposed to harsh environmental conditions. • Drought and heat stress combination caused in citrus a specific metabolic response. • Rootstock influences metabolic responses of scion to abiotic stresses. • Proline is a key compound in citrus tolerance to drought and heat combination. • Carrizo rootstock improves metabolic response of scion to stress combination.

Pest categorisation of Resseliella citrifrugis.

The EFSA Panel on Plant Health performed a pest categorisation of the citrus fruit midge, Resseliella citrifrugis Jiang (Diptera: Cecidomyiidae), for the territory of the EU. This species is not included in EU Commission Implementing Regulation 2019/2072. This oligophagous species, which feeds on Citrus spp. fruits, is known to occur in China (provinces of Fujian, Gansu, Guangdong, Guangxi, Guizhou, Hubei, Hunan, Jiangxi and Sichuan). First‐generation adults emerge in April and oviposit on the peduncle and calyx of citrus fruits. Larvae feed on the albedo (the white layer between skin and pulp) of the fruit, which they tunnel. Infested fruit most often drop prematurely. Larvae pupate either within the fallen fruit or in the soil. This species has three main peaks of activity (May, June–July, August–September) and four generations per year in its native range. Mature larvae from the last generation are the overwintering stage. Potential entry pathways for R. citrifrugis, such as Citrus spp. plants for planting with foliage and soil/growing media, and soil/growing media can be considered as closed. The citrus fruit pathway remains open from countries where R. citrifrugis is known to occur. Indeed, this species was intercepted in fresh pomelos 11 times from December 2020 to January 2021 in the EU. Should R. citrifrugis enter the EU, the ample availability of hosts (Citrus spp.) and the climatic conditions in citrus‐growing areas of southern EU Member States would most probably allow this species to successfully establish and spread. Economic impact in citrus production is anticipated if establishment occurs. R. citrifrugis satisfies the criteria that are within the remit of EFSA to assess for this species to be regarded as a potential Union quarantine pest. There is uncertainty about the nomenclature of R. citrifrugis and its exact host range. However, because the name Resseliella citrifrugis is used in multiple sources reporting it as a pest of citrus in China, where symptoms, biology and impact are described, these uncertainties do not affect the conclusions of this categorisation.

EFFECT OF PLANT GROWTH REGULATORS ON FRUIT SPLINTING IN THOMPSON NAVEL ORANGE

Fruit splitting is one of main problems extensively observed in citrus-growing area located in the northern parts of Iran. In order to investigate the effect of 2,4-D and GA3 on incidence of fruit splitting in Thompson ‘navel’ orange, an experiment, as a factorial arrangement in a randomized complete block design (RCBD) with three replications, was carried out in two consecutive years of 2016 and 2017. The main factors of this experiment included timing of spray at different growth stages (full bloom, petal fall, and June drop), 2, 4-D (0, 10, 20 mg L–1), and GA3 (0, 50, and 100 mg L–1). In the end of experiment, the characteristics including fruit length, fruit diameter, rind thickness, cellulase and polygalacturonase activities, total soluble solid, percentage of split fruit, and fruit yield were measured. Results showed that using 2, 4-D and GA3 not only decreased the rate of fruit splitting but also increased fruit yield as compared to controls. The highest fruit length, fruit diameter, rind thickness, total soluble solid and the lowest activities of cellulase and polygalacturonase were obtained using 100 mg L–1 GA3 and 20 mg L–1 2, 4 D during the full bloom. In general, the results revealed that using 2, 4-D and GA3 during the full bloom increased fruit yield while reduced fruit splitting and maintained the qualitative characteristics of Thompson ‘navel’ orange.

Biological control of the citrus leafminer 25 years after its introduction in the Valencia citrus growing area (Spain): A new player in the game

Natural enemies have been the key factor for the regulation of the citrus leafminer populations, Phyllocnistis citrella, since its introduction in Spain in 1993. The use of various broad-spectrum insecticides in citrus has been banned in recent years. This has led to an increase in the abundance and importance of the complex of generalist predators that inhabit the citrus canopy. In this work, we hypothesize that the incidence of P. citrella and the impact of its natural enemies would have changed due to the greater presence of generalist predators. Following the same protocols used in previous studies, three orchards located in Valencia, the major citrus-growing area of Spain, were monitored during 2017–2018. The incidence of P. citrella has decreased from 1.8 to 2.4 mines per leaf in 2006 to 0.93–1.98 in 2017–2018. This decrease could be attributed to the 43.0% increase of mortality by natural enemies compared to 2006. Currently, predation is the most important mortality factor. Predation resulted in 50.6% of the mortality caused by natural enemies compared to 34.6% in 2006. The first larval instar was the most susceptible to predation. Among the predators collected, the density of Pilophorus clavatus, a zoophytophagous mirid recently detected in Spanish citrus, was positively correlated with P. citrella predation. In the laboratory, females of P. clavatus preyed actively on second-instar P. citrella. Our results show the importance of conservation biological control in Spanish citrus and suggest that P. clavatus is occupying an important niche for the biological control of P. citrella.

Sodium hypochlorite: An economical technology for management of citrus gummosis

Among the different biotic stresses, gummosis/foot rot caused by Phytophthora nicotianae is the most severe and economically important disease in major citrus-growing areas of Punjab. It is increasingly becoming the major limiting factor in the successful cultivation of citrus in Hoshiarpur, Faridkot, Fazilka, Bathinda and Muktsar districts. This disease commonly occurs seriously during July-October following periods of high rainfall with warm temperatures and reduces the profitable life expectancy of trees. The research trials were conducted to manage citrus gummosis using sodium hypochlorite during 2015 to 2017 and this technology was also demonstrated at farmers’ orchards, Fazilka and Faridkot districts during 2017. Sodium hypochlorite @ 50 ml/10 litres of water/plant was found very effective in providing per cent recovery from trunk lesion and in reducing propagule density of the pathogen.

Ants (Hymenoptera: Formicidae) associated with scale insects (Hemiptera: Coccomorpha) on citrus trees in Coastal and Lower Eastern Counties, Kenya

A survey of citrus orchards was conducted in Kilifi, Kwale, Machakos and Makueni counties, Kenya to collect and identify ants (Hymenoptera: Formicidae) and natural enemies associated with scale insects (Hemiptera: Coccomorpha) feeding on citrus trees (Sapindales: Rutaceae). Nine ant species were found associated with nine scale insect species feeding on three citrus species (Citrus limon, C. reticulata and C. sinensis) for their honeydew. The ants associated with the scales in the study areas were: Cataulacus brevisetosus (Forel), Camponotus rufiglaucus (Jerdon), Crematogaster castanea (Smith), Cr. sjostedti (Mayr), Monomorium afrum (Andre), Myrmicaria opaciventris (Emery), Oecophylla longinoda (Latreille), Pheidole megacephalla (Fabricius), and Technomyrmex albipes (Fr. Smith). The ant Myrmicaria opaciventris was recorded attending four scale insects’ species: Coccus hesperidum, Co. viridis, Pulvinaria polygonata (Hemiptera: Coccidae) and Pseudococcus cryptus (Hemiptera: Pseudococcidae) in Kilifi County. Host-plant identities and localities surveyed are also presented. These new data for citrus-growing areas in Kenya will contribute to the development of integrated pest management programs on citrus.

Westward Palaearctic range expansion of Papilio demoleus Linnaeus, 1758 (Lepidoptera: Papilionidae) and its arrival at Mediterranean coastal regions of Turkey and Syria

We review the continuing and extensive spread of Papilio demoleus in south-eastern Turkey and in regions of Turkey and Syria adjacent to the north-eastern Mediterranean. Since the authors documented the arrival of this attractive but potentially destructive papilionid species at coastal areas of Syria in 2019, regular monitoring has confirmed successful overwintering there, as well as in Turkey. As previously indicated, P. demoleus is widely recognized as an invasive pest species in Citrus-growing areas of the world and hence its arrival is of potential economic importance to a region in which citrus is widely grown.