Premature Fruit Research Articles

Regulation of flowering in guava (Psidium guajava L.) cv. Lucknow-49

Plant growth hormones play a vital role in guava production and are used in the induction of flowering, help in fruit set, fruit thinning, fruit elongation, premature fruit drop prevention, fruiting buds development and inhibiting ripening process. These can also influence the size, appearance and quality parameters of fruits. By using plant hormones, an experiment was carried out in the Experimental Farm and Laboratory, Department of Horticulture, College of Agriculture, Assam Agricultural University, Jorhat during 2016–18 to regulate the flowering of guava in the rainy season and to increase more production and productivity of guava fruit in the winter season. A total of six treatments with four replications and two seasons (rainy and winter) were laid out in a randomized block design. The effect in foliar application of different concentrations of plant growth hormones of T1-Naphthalene acetic acid (NAA at 100 ppm), T2-Naphthalene acetamide (NAD at 40 ppm), T3-Naphthalene acetamide (NAD at 60 ppm), T4-Urea (2%), T5-Urea (5%) and T6-Urea (10%) at flowering stage in the month of April, 2017 helped in deblossoming of flowers, enhanced fruit size, weight, number of flowers and fruits, reduced fruit drop (76.43% in rainy season to 38.26%), decreased the days required for maturity (118 days) and increased the yield (20.73 kg/plant) in the winter season. The effect of NAD @ 60 ppm gave the best result in fulfilling all the physical parameters of the guava fruit in the winter season.

The Economics of Planting New Citrus Groves in Florida in the Era of HLB

Citrus greening, or huanglongbing (HLB), is a bacterial disease that affects citrus trees’ vascular systems, limiting nutrient uptake. As trees become increasingly affected by the disease, they suffer premature fruit drop, the fruit harvested is smaller and misshapen, and the juice quality is compromised, all resulting in lower yield. To this date there is no cure or successful management strategy to deal with HLB. This 8-page fact sheet written by Ariel Singerman, Marina Burani-Arouca, and Stephen H. Futch and published by the UF/IFAS Food and Resource Economics Department summarizes the results of an analysis of three tree densities under different production and market conditions to determine which density is most profitable. http://edis.ifas.ufl.edu/fe1050

The Effects of a Coating Treatment on Weight Loss, Juice Acidity, Shrinkage and Ethylene Evolution of Premature Passion Fruit:

The Effects of a Coating Treatment on Weight Loss, Juice Acidity, Shrinkage and Ethylene Evolution of Premature Passion Fruit:

Pest categorisation of Phyllostictasolitaria.

The Panel on Plant Health performed a pest categorisation of Phyllosticta solitaria, the causal agent of blotch of apple, for the EU. The pest is a well‐defined fungal species and methods are available for its detection and identification. P. solitaria is present in Canada and the continental states of the USA. The pest is not known to occur in the EU and is listed in Annex IAI of Directive 2000/29/EC, meaning its introduction into the EU is prohibited. The major cultivated host is Malus domestica (apple), but wild Malus and Crataegus species may also be affected. All hosts and major pathways of entry of the pest into the EU are currently regulated. The disease is favoured by warm, wet weather during the growing season. Host availability and climate matching suggest that P. solitaria could establish in parts of the EU and further spread mainly by human‐assisted means. The pest causes premature defoliation, fruit cracking and rot, and twig and branch cankers. At the beginning of the 20th century, disease incidences of 70–90% on fruit of untreated susceptible apple cultivars had been reported and the disease was considered as a limiting factor in the commercial production of those cultivars. Nowadays, the disease is rare in commercial apple orchards, probably due to regular fungicide sprays against other diseases. The pest introduction in the EU would potentially cause impacts to apple production. The main uncertainties concern the host range, the maximum distance of conidial dispersal by wind‐driven rain, and the magnitude of potential impacts to the EU. P. solitaria meets all the criteria assessed by EFSA for consideration as a potential Union quarantine pest. The criteria for considering P. solitaria as a potential Union regulated non‐quarantine pest are not met, since the pest is not known to occur in the EU.

Characteristics of Citrus Canker Lesions Associated with Premature Drop of Sweet Orange Fruit.

During the development of a citrus fruit, many cycles of infection by Xanthomonas citri subsp. citri may occur leading to the development of a range of characteristics of citrus canker lesions scattered across the fruit surface. This study aimed to determine whether the size of the lesions, their distance from the peduncle, and the number and time of appearance of the lesions on fruit of sweet orange were associated with premature fruit drop. A multiple linear regression analysis revealed a negative relationship between the fruit detachment force and the lesion diameter, the proximity of the nearest lesion to the peduncle and the number of lesions. A survival analysis demonstrated that these characteristics significantly influenced the probability and the time that a cankered fruit remained attached to the tree. More than 90% of dropped fruit had large lesions (>5 mm) but not all fruit with large lesions dropped before harvest. Approximately 50% of the harvested fruit had lesions >5 mm. On the harvested fruit remaining on the tree, although large, the lesions had a smaller diameter, were located farther from the peduncle, and were less numerous than those observed on dropped fruit. Small canker lesions neither reduced the detachment force nor the survival of fruit in the tree. The earlier a fruit expressed canker symptoms, the higher the probability the fruit developed large lesions near the peduncle and/or developed lesions in greater numbers. This study provides a better understanding on the relationship between the time of appearance of lesions of citrus canker on fruit and premature fruit drop. This information defines the critical period for fruit protection and may be used to improve disease management.

Genome-wide analysis of genes encoding MBD domain-containing proteins from tomato suggest their role in fruit development and abiotic stress responses.

In tomato, DNA methylation has an inhibitory effect on fruit ripening. The inhibition of DNA methyltransferase by 5-azacytidine results in premature fruit ripening. Methyl CpG binding domain (MBD) proteins are the readers of DNA methylation marks and help in the recruitment of chromatin-modifying enzymes which affect gene expression. Therefore, we investigate their contribution during fruit development. In this study, we identified and analyzed 18 putative genes of Solanum lycopersicum and Solanum pimpinellifolium encoding MBD proteins. We also identified tomato MBD syntelogs in Capsicum annum and Solanum tuberosum. Sixty-three MBD genes identified from four different species of solanaceae were classified into three groups. An analysis of the conserved domains in these proteins identified additional domains along with MBD motif. The transcript profiling of tomato MBDs in wild-type and two non-ripening mutants, rin and Nr, indicated constructive information regarding their involvement during fruit development. When we performed a stage-specific expression analysis during fruit ripening, a gradual decrease in transcript accumulation in the wild-type fruit was detected. However, a very low expression was observed in the ripening mutants. Furthermore, many ethylene-responsive cis-elements were found in SlMBD gene promoters, and some of them were induced in the presence of exogenous ethylene. Further, we detected the possible role of these MBDs in abiotic stresses. We found that few genes were differentially expressed under various abiotic stress conditions. Our results provide an evidence of the involvement of the tomato MBDs in fruit ripening and abiotic stress responses, which would be helpful in further studies on these genes in tomato fruit ripening.

Peach Scab

There are many peach diseases that can affect fruit quality and the marketability of the produce. Blemishes to the skin or within the flesh can be a reason to reject an entire fruit load or significantly reduce the purchasing price. Peach scab is a disease caused by the fungus Cladosporium carpophilum (Figure 1). The pathogen can infect twigs, leaves, and fruits, where it can cause lesions that can affect fruit quality, marketability, and in extreme cases can cause cracking of the fruit and premature fruit drop. Peach scab is typical during periods of humid weather because rain splashes the conidia (asexual spores) from the fungus between leaves, twigs, and fruit in the tree canopy, which spreads the disease. This pathogen can infect other fruits and nuts within the Prunus species, like almonds, apricots, nectarines, and plums. This 6-page fact sheet is a minor revision written by Daniel Mancero-Castillo, Ali Sarkhosh, Mercy Olmstead, and Phillip Harmon, and published by the Horticultural Sciences Department, August 2018. HS1249/HS1249: Peach Scab (ufl.edu)

Promising primers for detection of phytoplasma causing coconut lethal yellowing disease in Mozambique

Coconut is one of the main cash crop in Mozambique, which occupied the second position after Tanzania in coconut production in Africa. Coconut production was drastically affected by the occurrence of a devastating Coconut Lethal Yellowing Disease (CLYD) epidemics, which reduced significantly the coconut yields. CLYD symptoms triggered upon phytoplasma infection, i.e. premature fruit dropping, necrosis of the inflorescence and progressive yellowing of the leaves, are used to identify infected trees. However, the diagnostic based uniquely on symptoms is not conclusive to confirm infection, and needs to be confirmed by molecular methods. In this study, three previously described reference primers for phytoplasma detection were tested on infected samples collected in Mozambique. Since those primers gave incongruent results, 20 new primer pairs targeting the 16S rDNA region, were newly designed. To evaluate their performance in detecting coconut infecting phytoplasma, 108 samples were tested and selected positive samples confirmed by sequencing. Our results showed a new primer pair more accurate and reliable compared to the reference pairs for CLYD detection in Mozambique. Moreover, the new primer pair was able to detect a new putative phytoplasma variant in Mozambique. Therefore, this study makes an important contribution to CLYD phytoplasma molecular diagnostics and its causative agent, giving insights that may be applied to the study of CLYD phytoplasma infection systems.

Integrated control of aerial fungal diseases of olive

Foliar and fruit fungal diseases are responsible for severe yield losses in olives (Olea europaea L.) in most olive-growing areas around the world. Among the most important are leaf spot, anthracnose, cercosporiosis and drupe rot, respectively caused by Fusicladium oleagineum, Colletotrichum spp., Pseudocercospora cladosporioides and Botryosphaeria dothidea. Symptoms vary from tree defoliation, twig dieback, premature fruit fall and drupe rot, which can completely destroy olive production and reduce olive oil quality. Copper-based products and a few other compounds represent almost the only fungicides used to date to control aerial fungal diseases of olive. Moreover, although still permitted, the European authorities would like to see a ban on copper fungicides in conventional and organic farming across Europe, which would have a major impact on disease management in olive production. Under Directive 2009/128, the Sustainable Use Directive, National Action Plans for reductions in pesticide use, and the implementation of Integrated Pest Management on all farms in member states were reviewed by the European Union at the end of 2014 and became mandatory throughout member states. Extensive field trials conducted in southern Italy in recent years demonstrate that aerial fungal diseases of olive can be effectively controlled in an integrated management approach, using appropriately timed application of traditional fungicides and organically approved plant protection compounds, such as sulphur. Particularly, a new sulphur-based product, Thiopron®, was as effective as traditional fungicides in controlling both olive cercosporiosis and drupe rot caused by different fungal species.

First report of almond moth, Cadra cautella as a cause of premature fruit drop in tree bean, Parkia Roxburghii g don

First report of almond moth, <i>Cadra cautella</i> as a cause of premature fruit drop in tree bean, <i>Parkia Roxburghii</i> g don

First Report of the 16SrIV-D Phytoplasma Associated with Decline of a Bismarck Palm (Bismarckia nobilis)

The Bismarck palm (Bismarckia nobilis Hildebr. &amp; H. Wendl), with blue-gray leaves, is an important ornamental palm commonly planted along the highways in central and south Florida. During May of 2017, severe discoloration of the younger leaves of a Bismarck palm was observed in a roadside landscape in Manatee County, Florida. Symptoms of Texas Phoenix palm decline can include premature fruit drop, death of inflorescences, more than usual discoloration of the oldest leaves, and death of the spear leaf. The presence of the 16SrIV-D phytoplasma was confirmed on Bismarck palm.

Pest categorisation of small-spored Alternaria carrying the genes for the AM- or AK-toxin biosynthesis.

The Panel on Plant Health performed a pest categorisation of small‐spored Alternaria carrying the genes for the AM‐ or AK‐toxin biosynthesis, for the EU. The identity of the pests is clearly defined and reliable methods exist for their detection/identification. They are listed in Annex IIAI of Directive 2000/29/EC as Alternaria alternata (non‐European pathogenic isolates). Their distribution in the EU is restricted though with some uncertainty. The AM‐toxin producer Alternaria affect Malus spp. and Pyrus communis (European pear), whereas the AK‐toxin producer affect Pyrus pyrifolia, Pyrus bretschneideri and Pyrus ussuriensis (Asian pears). The pests could potentially enter the EU on host‐planting material and fruit originating in infested countries. There are no biotic/abiotic factors limiting their potential establishment and spread in the EU, as their epidemiology is similar to that of other well‐established Alternaria spp. Apples and European pears are widespread in the EU; Japanese pears are also present, but no data was found on their abundance/distribution. In the infested areas, the pests cause premature defoliation, fruit spotting and rot resulting in yield/quality losses. It is expected that the introduction and spread of the pests in the EU could impact apple and pear production, although the magnitude is unknown. Cultural practices and chemical measures may reduce the inoculum and the disease, but they cannot eliminate the pests. Phytosanitary measures are available to mitigate the risk of introduction and spread of the pests. The pests do not meet all the criteria assessed by EFSA for consideration as potential Union quarantine pests, as they are not under official control in those EU restricted areas where they have been found. The pests do not meet all the criteria assessed by EFSA to consider them as Union regulated non‐quarantine pests, as host plants for planting are not the main means of pest spread.

First Report of Colletotrichum acutatum Causing Anthracnose on Olives in Albania.

Olive trees (Olea europaea L.) are among the most important fruit tree crops grown in Albania, covering an estimated 8% of the arable land of this country. The highest amount of olive production in Albania is concentrated in the coastal districts of Fier, Berat, Elbasan, Lezha, Tirana, Kruja and Vlora, all with Mediterranean climate conditions. Anthracnose is the main disease of olive fruit caused by different Colletotrichum spp. primarily belonging to two complexes, C. acutatum sensu lato (s.l.) and C. gloeosporioides s.l. (Cacciola et al. 2012; Schena et al. 2014.). On July 2018, field observations of about 50 olive trees in the Ishull Shengjin Lezhe Region (54% prevalence), 1 km away from the coast showed severe symptoms of mummified olive fruits in about 20 to 40% disease incidence and 30% disease severity of the Italian table olive cv. Frantoio trees resulting in premature fruit drop or mummification. The causal agent was isolated directly from infected fruits on potato dextrose agar and Rose Bengal nutrient media. Microscopic examinations of five single spore isolated fungal colonies showed acervuli with typical conidia of the genus Colletotrichum that were aseptate, straight, hyaline, subcylindrical with rounded ends and 12.3 to 22.1 µm long (mean = 17.4 µm) and 2.5 to 7.3 µm wide (mean = 5.9 µm) (n= 50 conidia) (Damm et al. 2012). To identify the fungal species, DNA from two single-spore isolates (Col-3-ALB and Col-9-ALB) isolated from fruits was extracted, and six genes were amplified (ITS, GAPDH, CHS-1, HIS3, ACT, and TUB2) using the primers reviewed in Damm et al. (2012). PCR products were sequenced, and BLAST analysis showed 100% identity to C. acutatum for both isolates (GenBank accession nos. for Col-9-ALB MT218337 [ITS1-5.8-ITS2], MT274748 [CHS-1], MT274749 [HIS3], MT274750 [GAPDH], MT274751 [TUB2], and MT274752 [ACT]). Phylogenetic analysis using the concatenated sequences of Col-9-ALB, the type species of C. acutatum (112996), a previously identified published Greek C. acutatum isolate (O9) and three C. godetiae strains confirmed the identification of Col-9-ALB as C. acutatum. Pathogenicity tests were performed in the laboratory to confirm the ability of C. acutatum isolates to cause disease on olive drupes. Fruits were surface disinfected with 0.1% NaClO for 3 min and rinsed with ddH2O. Artificial inoculations with the two above isolates were performed by spraying 24 olive fruits per isolate cv. Kalamon (eight olive fruits per replication) with a spore suspension (106 conidia/ml). Olive fruits sprayed with sterilized water served as untreated control. After inoculation, olive fruits were placed in closed sterile plastic boxes and kept at 26°C with a 12-h photoperiod. First rot symptoms and formation of acervuli by the pathogen were initiated 3 days after inoculation. Eight days post-inoculation, all treatments exhibited typical anthracnose symptoms similar to those observed in olive orchards (extensive fruit rot). To fulfil Koch's postulates, C. acutatum was re-isolated from 10 random symptomatic olive fruits/isolate and their identity was confirmed from all samples. To our knowledge, this is the first report of C. acutatum causing fruit rot on olive trees in Albania. It is important to further study the epidemiology for the disease under local climate conditions and on different olive cultivars in order to develop effective management strategies for this very destructive disease of olive.

Pest categorisation of Venturia nashicola.

The Panel on Plant Health performed a pest categorisation of Venturia nashicola, the causal agent of Asian pear scab, for the European Union (EU). The pathogen is a well‐defined, distinguishable fungal species affecting Pyrus pyrifolia var. culta, P. ussuriensis and P. bretschneideri in Asian countries. P. communis (European pear) is not a host of V. nashicola, but the host status of other Pyrus species is unclear. V. nashicola is not known to occur in the EU. It is listed in Annex IIAI of Directive 2000/29/EC. The pathogen could potentially enter the EU on host plants for planting and fruit originated in infested countries. There are no climatic factors limiting the potential establishment and spread of the pathogen in the EU, as its epidemiology is similar to those of Venturia inaequalis (apple scab) and Venturia pyrina (European pear scab), which are well‐established in the EU. The hosts are present in the EU, but no data were found on their abundance and distribution. In the infested areas, V. nashicola causes premature leaf and fruit drop and fruit distortion resulting in considerable yield/quality losses. The introduction of the pathogen into the EU could cause yield/quality losses and environmental consequences because of the additional fungicide sprays for disease control. Cultural practices and chemical measures applied in the infested areas reduce the inoculum sources but they cannot eliminate the pathogen. Phytosanitary measures are available to mitigate the risk of introduction and spread of the pathogen in the EU. All criteria assessed by EFSA for consideration as a potential Union quarantine pest are met. As V. nashicola is not known to occur in the EU, this criterion assessed by EFSA to consider it as a Union regulated non‐quarantine pest is not met.

Irrigation Management of HLB-Affected Trees

Water is a limiting factor in Florida citrus production during the majority of the year because of the low water holding capacity of sandy soils resulting from low clay and the non-uniform distribution of the rainfall. In Florida, the major portion of rainfall comes in June through September. However, rainfall is scarce during the dry period from February through May, which coincides with the critical stages of bloom, leaf expansion, fruit set, and fruit enlargement. Irrigation is practiced to provide water when rainfall is not sufficient or timely to meet water needs. Proper irrigation scheduling is the application of water to crops only when needed and only in the amounts needed; that is, determining when to irrigate and how much water to apply. With proper irrigation scheduling, yield will not be limited by water stress. With citrus greening (HLB), irrigation scheduling is becoming more important and critical and growers cannot afford water stress or water excess. Any degree of water stress or imbalance can produce a deleterious change in physiological activity of growth and production of citrus trees. The number of fruit, fruit size, and tree canopy are reduced and premature fruit drop is increased with water stress. Extension growth in shoots and roots and leaf expansion are all negatively impacted by water stress. Other benefits of proper irrigation scheduling include reduced loss of nutrients from leaching as a result of excess water applications and reduced pollution of groundwater or surface waters from the leaching of nutrients. Recent studies have shown that for HLB-affected trees, irrigation frequency should increase and irrigation amounts should decrease to minimize water stress from drought stress or water excess, while ensuring optimal water availability in the rootzone at all times.

Citrus Irrigation Management

Water is a limiting factor in Florida citrus production during the majority of the year because of the low water holding capacity of sandy soils resulting from low clay and the non-uniform distribution of the rainfall. In Florida, the major portion of rainfall comes in June through September. However, rainfall is scarce during the dry period from February through May, which coincides with the critical stages of bloom, leaf expansion, fruit set, and fruit enlargement. Irrigation is practiced to provide water when rainfall is not sufficient or timely to meet water needs. Proper irrigation scheduling is the application of water to crops only when needed and only in the amounts needed; that is, determining when to irrigate and how much water to apply. With proper irrigation scheduling, yield will not be limited by water stress. With citrus greening (HLB), irrigation scheduling is becoming more important and critical and growers cannot afford water stress or water excess. Any degree of water stress or imbalance can produce a deleterious change in physiological activity of growth and production of citrus trees. The number of fruit, fruit size, and tree canopy are reduced and premature fruit drop is increased with water stress. Extension growth in shoots and roots and leaf expansion are all negatively impacted by water stress. Other benefits of proper irrigation scheduling include reduced loss of nutrients from leaching as a result of excess water applications and reduced pollution of groundwater or surface waters from the leaching of nutrients. Recent studies have shown that for HLB-affected trees, irrigation frequency should increase and irrigation amounts should decrease to minimize water stress from drought stress or water excess, while ensuring optimal water availability in the rootzone at all times.

Xanthomonas campestris pv. musacearum: a major constraint to banana, plantain and enset production in central and east Africa over the past decade.

Bacteria; Phylum Proteobacteria; Class Gammaproteobacteria; Order Xanthomonadales; Family Xanthomonadaceae; Genus Xanthomonas; currently classified as X. campestris pv. musacearum (Xcm). However, fatty acid methyl ester analysis and genetic and genomic evidence suggest that this pathogen is X. vasicola and resides in a separate pathovar. Xcm can be isolated on yeast extract peptone glucose agar (YPGA), cellobiose cephalexin agar and yeast extract tryptone sucrose agar (YTSA) complemented with 5-fluorouracil, cephalexin and cycloheximide to confer semi-selectivity. Xcm can also be identified using direct antigen coating enzyme-linked immunosorbent assay (DAC-ELISA), species-specific polymerase chain reaction (PCR) using GspDm primers and lateral flow devices that detect latent infections. Causes Xanthomonas wilt on plants belonging to the Musaceae, primarily banana (Musa acuminata), plantain (M. acuminata × balbisiana) and enset (Ensete ventricosum). There is a high level of genetic homogeneity within Xcm, although genome sequencing has revealed two major sublineages. Yellowing and wilting of leaves, premature fruit ripening and dry rot, bacterial exudate from cut stems. Xcm has only been found in African countries, namely Burundi, Ethiopia, Democratic Republic of the Congo, Kenya, Rwanda, Tanzania and Uganda. Xcm is transmitted by insects, bats, birds and farming implements. Long-distance dispersal of the pathogen is by the transportation of latently infected plants into new areas. The management of Xcm has relied on cultural practices that keep the pathogen population at tolerable levels. Biotechnology programmes have been successful in producing resistant banana plants. However, the deployment of such genetic material has not as yet been achieved in farmers' fields, and the sustainability of transgenic resistance remains to be addressed.

Αn assessment of components of crop loss due to infestation by Dacus oleae, in Corfu

An assessment of components of crop loss caused by the olive fly, Dacus oleae, was carried out in Corfu during the years 1976-1979. The results indicate that the most important component of crop loss due to D. oleae infestation is the preharvest fruit drop induced, mainly, by the third stage larva. Using three starting dates, which coincided with the main periods of infestation between July and October, estimates were made of the proportions of infested fruits induced to fall prematurely before the start of harvesting in November. The larva of D. oleae consumes only a small proportion of the fruit pulp (on average 4.48 %). The effect of infestation on the acidity of the oil is indirect and it is important only when the fruits remain for over a week on the ground before they are collected. Compensation by the tree for premature fruit drop caused by D. oleae infestation does not appear to be of any significance in assessing crop loss.

Sexual Reproduction in the Citrus Black Spot Pathogen, Phyllosticta citricarpa.

Citrus black spot (Phyllosticta citricarpa) causes fruit blemishes and premature fruit drop, resulting in significant economic losses in citrus growing areas with summer rainfall across the globe. The mating type locus of P. citricarpa has recently been characterized, revealing the heterothallic nature of this pathogen. However, insight into the occurrence of mating and the impact of completing the sexual cycle of P. citricarpa was lacking. To investigate the occurrence and impact of sexual reproduction, we developed a method to reliably, and for the first time, produce ascospores of P. citricarpa on culture media. To demonstrate meiosis during the mating process, we identified recombinant genotypes through multilocus genotyping of single ascospores. Because the process of fertilization was not well understood, we experimentally determined that fertilization of P. citricarpa occurs via spermatization. Our results demonstrate that P. citricarpa is heterothallic and requires isolates of different MAT idiomorphs to be in direct physical contact, or for spermatia to fulfill their role as male elements to fertilize the receptive organs, in order to initiate the mating process. The impact of mating on the epidemiology of citrus black spot in the field is discussed.

First Report of Copper-resistant Xanthomonas citri pv. citri Pathotype A Causing Asiatic Citrus Canker in Réunion, France

Xanthomonas citri pv. citri causes Asiatic citrus canker (ACC), which induces erumpent, callus-like lesions on all aerial organs, and consequently defoliation, premature fruit drop, and twig dieback under high inoculum pressure. Present in most tropical and subtropical citrus producing regions, the disease can lead to important decreases in yield and limitations to export markets due to the quarantine status of the pathogen in some countries ( Graham et al. 2004 ). Strains assigned to genetic lineage 1 within pathotype A, which has the widest host range comprising most citrus cultivars and citrus relatives, were shown to be primarily involved in the worldwide expansion of the bacterium over the 20th century ( Pruvost et al. 2014 ). ACC has been considered endemic in Reunion Island since the 1970s, but was likely present earlier and was not subjected to any eradication attempt. Most citrus growers on the island frequently apply copper-based pesticides as part of integrated pest management programs. A recurring lack of ACC control in several citrus groves was investigated in 2014 using our lab collection of authenticated X. citri pv. citri strains. A total of 501 strains from active epidemics as well as 123 historical strains isolated from 1978 onward were tested for copper resistance using PCR assays targeting copL ( Behlau et al. 2013 ). A total of 115 strains produced the expected amplicon whereas others (including all historical strains) and the negative control (H 2 O) did not. Phenotypic tests were carried out on low-complexing mineral salts casitone-yeast extract-glycerol-agar (CYE) plates ( Zevenhuizen et al. 1979 ) flooded with bacterial suspensions ( ≈ 5 × 10 6 cfu ml –1 ) in sterile tris buffer (pH 7.2), allowed to dry for 15 min., inoculated with a sterile CuSO 4 , 5H 2 O solution (10 mg ml –1 ) with an easySpiral plater used to create a gradient of log-increasing copper concentrations toward the plate center and incubated for 2 days at 28°C. Using this assay, copL + strains grew over a radius (measured from the plate periphery where the concentration of copper are lowest) >23 mm whereas copL – strains growth radius were constantly lower. Copper-resistant strains (CRS) had minimum inhibitory concentrations for copper sulfate ranging from 128 to 256 μ l ml –1 ( Pruvost et al. 1998 ). A subset of 20 CRS and 40 copper-susceptible strains (CSS) (including historical strains) were all assigned to genetic lineage 1 by minisatellite typing (performed as reported by Pruvost et al. 2014 ) and split into two multilocus haplotypes shared also with CSS. CRS were widespread in most citrus production areas of the island where they coexisted with CSS. The oldest CRS dated from 2010. Because no extreme hurricane hit the island between 2010 and 2014, the fast spread of CRS over the island was very likely related to their presence in a major citrus nursery, as confirmed by our data. In Reunion, the European Conformitas Agraria Communitatis (CAC) standards (directive 92/34/EEC) certify the disease-free status of citrus nursery plants (assessed by visual inspections for ACC). CAC is presently recommended but not compulsory. This report suggests that a strict implementation of this procedure would have helped limiting the spread of CRS in Reunion. (Resume d'auteur)