Citrus Field Research Articles

A remote sensing extraction method for the area of a multi-featured citrus field in Jiangxi, Southeast China

A remote sensing extraction method for the area of a multi-featured citrus field in Jiangxi, Southeast China

Isolation and Identification of Antifungal Bacteria from Rhizosphere of Citrus Field

Isolation and Identification of Antifungal Bacteria from Rhizosphere of Citrus Field

Determining leaf nutrient concentrations in citrus trees using UAV imagery and machine learning

Nutrient assessment of plants, a key aspect of agricultural crop management and varietal development programs, traditionally is time demanding and labor-intensive. This study proposes a novel methodology to determine leaf nutrient concentrations of citrus trees by using unmanned aerial vehicle (UAV) multispectral imagery and artificial intelligence (AI). The study was conducted in four different citrus field trials, located in Highlands County and in Polk County, Florida, USA. In each location, trials contained either ‘Hamlin’ or ‘Valencia’ sweet orange scion grafted on more than 30 different rootstocks. Leaves were collected and analyzed in the laboratory to determine macro- and micronutrient concentration using traditional chemical methods. Spectral data from tree canopies were obtained in five different bands (red, green, blue, red edge and near-infrared wavelengths) using a UAV equipped with a multispectral camera. The estimation model was developed using a gradient boosting regression tree and evaluated using several metrics including mean absolute percentage error (MAPE), root mean square error, MAPE-coefficient of variance (CV) ratio and difference plot. This novel model determined macronutrients (nitrogen, phosphorus, potassium, magnesium, calcium and sulfur) with high precision (less than 9% and 17% average error for the ‘Hamlin’ and ‘Valencia’ trials, respectively) and micro-nutrients with moderate precision (less than 16% and 30% average error for ‘Hamlin’ and ‘Valencia’ trials, respectively). Overall, this UAV- and AI-based methodology was efficient to determine nutrient concentrations and generate nutrient maps in commercial citrus orchards and could be applied to other crop species.

Unmanned air vehicle based high resolution imagery for chlorophyll estimation using spectrally modified vegetation indices in vertical hierarchy of citrus grove

Chlorophyll is a significant indicator of plant vigor and plant health which enables to estimate final crop yield. Current experiment was conducted to acquire high resolution multispectral image from UAV and accurately estimate chlorophyll contents using spectral chlorophyll indices in vertical crop plantation. Ground truthing was performed by taking chlorophyll values from citrus leaves using (SPAD-502 Minolta) chlorophyll meter. Five vegetation indices including DVI (difference vegetation index), RDVI (renormalized difference vegetation index), MTVI2 (modified triangular vegetation index 2), SARVI (soil and atmospherically resistant vegetation index) and Iron Oxide index were derived to determine most robust index by developing linear regression models among VIs and citrus leaves chlorophyll contents. Triangular indices (MTVI2) expressed highest correlation coefficient R2 = 0.81 with high accuracy and precision for ground truthed citrus leaves chlorophyll contents. MTVI2 and SARVI were proven as most robust indices to map spatial differences in chlorophyll content with R2 = 0.81 and R2 = 0.76, respectively. DVI, RDVI and Iron Oxide index resulted in less efficient VIs in vertical plantations with coefficient of determination (R2) values 0.57, 0.59 and 0.69, respectively. Moreover, in this study low cost multispectral UAV (DJI Phantom4 Pro) was used to monitor biophysical status of crop in real time and develop an on-field cost efficient, precise and accurate agricultural monitoring system against conventional techniques. This article has covered the aspect of chlorophyll detection using spectrally modified VIs in vertical hierarchy that was a citrus field and manual efforts were used by taking the help of UAV. The novel aspect of this study covers the chlorophyll detection in the trees which is not studied by the scientists as a part of Remotesensing.

Soil Parameter Mapping in Sloped Citrus Field Using a Portable Spectrophotometer

Soil Parameter Mapping in Sloped Citrus Field Using a Portable Spectrophotometer

Exploring the use of Unmanned Aerial Vehicles (UAVs) with the simplified ‘triangle’ technique for soil water content and evaporative fraction retrievals in a Mediterranean setting

ABSTRACT Information acquired from Unmanned Aerial Vehicles (UAVs) is frequently used nowadays in a variety of disciplines and research fields. The present study explores for the first time the combined use of UAVs with a newly proposed technique for estimating evaporative fraction (EF) and surface soil moisture (SSM). The investigation is performed in a typical Mediterranean setting, a citrus field with flat topography divided in two plots with different irrigation schemes, in Sicily, Italy, at which ground data acquired during an extensive field campaign in July 2019. Reasonable estimates of both EF and surface wetness were produced, with patterns in agreement to vegetation cover fragmentation, topography, and other site-specific characteristics. Validation shows average error of 0.053 for EF and of 0.040 cm3 cm−3 for SSM. The results are comparable or better to those reported in analogous studies performed in similar areas. This implies that the investigated approach performs well under the semi-arid conditions characterizing the experimental set up. To our knowledge, this study represents the first evaluation of the combined use of the ‘simplified triangle’ with very high-resolution UAV imagery. As such, the findings are of significance regarding the potential future use of the ‘simplified triangle’ approach particularly with very fine resolution imagery such as that provided by UAV for mapping and monitoring EF and SSM in agricultural and natural ecosystems.

Influence of Altered Microbes on Soil Organic Carbon Availability in Karst Agricultural Soils Contaminated by Pb-Zn Tailings.

Soil organic carbon (SOC) availability is determined via a complex bio-mediated process, and Pb-Zn tailings are toxic to the soil microbes that are involved in this process. Here, Pb-Zn-tailings- contaminated karst soils with different levels (paddy field > corn field > citrus field > control group) were collected to explore the intrinsic relationship between Pb-Zn tailings and microbes due to the limited microbial abundance in these soils. The SOC concentration in the paddy fields is the highest. However, based on the soil microbial diversity and sole-carbon-source utilization profiles, the rate of SOC availability, McIntosh index, Shannon-Wiener diversity index, Simpson’s diversity index and species richness are the lowest in the rice paddy soils. According to the results of Illumina sequencing of the 16S rRNA gene, Acidobacteria and Proteobacteria are the dominant phyla in all samples, accounting for more than 70% of the reads, while the majority of the remaining reads belong to the phyla Verrucomicrobia, Chloroflexi, Actinobacteria, Bacteroidetes, and Nitrospirae. We also observed that their class, order, family, genus and operational taxonomic units (OTUs) were dependent on SOC availability. Pearson correlation analysis reveals that L-asparagine utilization profiles show significant positive correlation with OTUs 24, 75, and 109 (r = 0.383, 0.350, and 0.292, respectively), and malic acid utilization profiles show significant positive correlation with OTUs 4, 5, 19, 27 (Bradyrhizobium), 32 (Burkholderia), 75 and 109 (r = 0.286, 0.361, 0.387, 0.384, 0.363, 0.285, and 0.301, respectively), as also evidenced by the redundancy analysis (RDA) biplot and heat map. These results indicate that the most abundant groups of bacteria, especially the uncultured facultative Deltaproteobacteria GR-WP33-30 (OTU 24), after long-term acclimation in heavy metal-contaminated soil, are associated with the variance of labile carbon source such as L-asparagine and may have considerable control over the stability of the vast SOC pool in karst surface soils with different agricultural land-use practices. These findings can expand our understanding of global soil-carbon sequestration and storage via changes in microbial community structure of the most abundant species.

Evaluation of an operational real-time irrigation scheduling scheme for drip irrigated citrus fields in Picassent, Spain

Irrigated agriculture is very important for securing food production for an increasing population over the next decades. Given scarcity of water resources, optimal irrigation management is needed to reduce water while realizing maximal crop productivity. The new method of integrating soil water content measurements and the Community Land Model (CLM) using sequential data assimilation (DA) is promising to improve the prediction of soil water status and efficiently design irrigation strategies. Soil water content measured by FDR (Frequency Domain Reflectometry) was assimilated into CLM by LETKF (Local Ensemble Transform Kalman Filter) to improve model predictions. Atmospheric input data from GFS (Global Forecast System) were used to force CLM in order to predict short-term soil water contents. The irrigation amount was then calculated on the basis of the difference between predicted and targeted soil water content over the root zone.During the real-time irrigation campaigns in Picassent (Spain) in 2015 and 2016, there were 6 fields irrigated according the data assimilation-optimization approach (CLM-DA), 2 further fields according the FAO (Food and Agriculture Organization) water balance method and also 2 fields traditionally according the farmers preference. The required amount of irrigation water for each citrus field was applied by SCADA (supervisory control and data acquisition system). Compared with the traditionally irrigated fields by farmers, 24% less irrigation water was needed for the CLM-DA scheduled fields averaged over both years from July to September, while the FAO fields were irrigated with 22% less water. Stem water potential data and soil moisture recordings of the CLM-DA scheduled fields did not indicate significant water stress during the irrigation period. The CLM-DA scheduled fields received less irrigation water than traditionally irrigated fields, but the orange production was not significantly suppressed.Overall, our results show that the CLM-DA method is attractive given its water saving potential and automated approach, ease of incorporation of on-line measurements and ensemble based predictions of soil moisture evolution.

Carbon Metabolism Characteristics of the Karst Soil Microbial Community for Pb-Zn Mine Tailings

BIOLOG and 18S rRNA PCR-DGGE methods were used to estimate the characteristics of carbon source metabolism of the soil microbial community as well as the relationship between soil fungi and soil organic carbon in different karst land use types (corn field, citrus field, and paddy field) contaminated by Pb-Zn tailings at Sidi Village, Yangshuo, Guangxi Zhuang Autonomous Region, SW China. It was found that the concentrations of Pb, Zn, Cu, and Cd were highest in the paddy field, followed by the corn field, citrus field, and control group (dry field). In addition, the geo-accumulation index indicated that the heavy metal pollution at this area was caused by Pb and Cd and that Cd was the key environmental risk factor. With the Pb-Zn tailings, there was low microbial biomass carbon, biological entropy, and microbial carbon source metabolism in the soil samples. The highest soil organic carbon and heavy metal concentrations were found in the paddy field, followed by the corn field and citrus field. According to the DDGE results, it was found that Pycnoporus sp. ZW02.30 was found in control group soils, Fusarium solani and Fusarium oxysporum were found in the corn field and citrus field, and Penicillium decumbens was found in citrus field. These were involved in the degradation of sugars, such as starch, cellulose, hemicellulose, and lignin. However, the fungi were not found in the paddy field. Based on the low functional diversity of the soil microbial community and biological entropy as well as the high soil organic carbon concentration in the paddy field, it was concluded that soil microbial carbohydrate metabolism and the mineralization rate of the soil organic carbon was controlled by soil microorganisms, especially fungi, in different land use soils in the karst area contaminated by Pb-Zn tailings.

Quasi-Real-Time Monitoring of a Citrus Field in Nabeul and Joumine Dam in Tunisia

The management of remote natural resources, e.g., land and water resources, requires frequent visits to these sites which could be costly in time and resources. Telemetry technologies help monitoring, observing and analyzing data at a distance; they use advanced information and communication protocols and have been applied to different applications including agricultural fields. The objective of this study was to evaluate the performance of a new telemetry technology, a field network system, to remotely monitoring natural resources (a citrus grove in the governorate of Nabeul and the dam of Joumine in the governorate of Bizerte) in Tunisia. The field network system, installed in these two remote locations and powered with solar panels, run well during the test periods. Although the system sent data daily, data transfer stability was a challenge that should be further studied and improved. The manuscript further reports on the quantitative and qualitative performance of the system in Tunisia. Overall, the field network system is a tool that could be used for different applications by researchers, agricultural producers, water resources managers, and policy makers.

Toxicity of selected biorational insecticides to Pulvinaria aurantii Cockerell and its predator, Cryptolaemus montrouzieri Mulsant in citrus field

ABSTRACTThe citrus cottony scale, Pulvinaria aurantii Cockerell, is the most important pest of citrus orchards in northern Iran in recent years. Owing to the harmful impacts of chemical insecticides, the use of biorational pesticides seems a safe and convenient way to control this pest. The present investigation was set up to study contact toxicity of various biorational and chemical compounds on the first, second instar nymph and overwintering adult of the citrus cottony scale, P. aurantii, and its predator, Cryptolaemus montrouzieri Mulsant under field conditions. The results indicated that the highest percentage of mortality of first instar nymph of the citrus cottony scale was observed in the Dayabon treatment of 9 and 10 ml/L, 100.0% ± 0.0% and the lowest percentage was observed in Palizin treatment of 1.5 ml/L, 34.7% ± 2.9%. In the second instar nymph, the highest mortality was seen in the Dursban treatment of 2 ml/L, 94.7% ± 2.4% and the lowest mortality in the Palizin treatment of 1.5 ml/L, 30.0% ± 2.3%. Also, for overwintering adults Dayabon 10 ml/L caused the highest mortality, 96.0% ± 4.0% during 24 h. In the case of ladybird insects, the highest and lowest percentage of mortality was observed in the Dursban treatment of 2 ml/L, 76.7% ± 8.8%, Dayabon 5 ml/L, and Palizin 2 ml/L, 3.3% ± 3.3%, respectively. The highest and lowest mortality rate of larvae of ladybird was estimated in the Dursban treatment of 2 ml/L, 83.3% ± 3.3% and Dayabon 5 ml/L, 3.3% ± 3.3%, respectively. Also, for overwintering predator adults Palizin 1.5 ml/L had the lowest mortality, 3.3% ± 3.3% during 24 h and this rate remain unchanged after 96 h after treatment. According to the results obtained, treatments with Dayabon 9 and 10 ml/L, can be a viable alternative to other high-risk chemical pesticides in addition to effectively controlling citrus cottony scale without having any adverse impacts on predator ladybird.

First Report of Paecilomyces variotii Isolated From Citrus Psyllid (Diaphorina citri), the Vector of Huanglongbing of Citrus, in China

HomePlant DiseaseVol. 100, No. 12First Report of Paecilomyces variotii Isolated From Citrus Psyllid (Diaphorina citri), the Vector of Huanglongbing of Citrus, in China PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Paecilomyces variotii Isolated From Citrus Psyllid (Diaphorina citri), the Vector of Huanglongbing of Citrus, in ChinaX. B. Song, L. H. Zhang, A. T. Peng, B. P. Cheng, and J. F. LingX. B. SongSearch for more papers by this author, L. H. ZhangSearch for more papers by this author, A. T. PengSearch for more papers by this author, B. P. ChengSearch for more papers by this author, and J. F. LingSearch for more papers by this authorAffiliationsAuthors and Affiliations X. B. Song , Agricultural College of South China Agricultural University, Guangdong Province, Key Laboratory of Microbial Signals and Disease Control, Guangzhou 510640, China, and Plant Protection Research Institute, Guangdong Academy of Agricultural Sciences, Guangdong Provincial Key Laboratory of High Technology for Plant Protection, Guangzhou 510640, China L. H. Zhang , Agricultural College of South China Agricultural University, Guangdong Province, Key Laboratory of Microbial Signals and Disease Control, Guangzhou 510640, China A. T. Peng B. P. Cheng J. F. Ling , Plant Protection Research Institute, Guangdong Academy of Agricultural Sciences, Guangdong Provincial Key Laboratory of High Technology for Plant Protection, Guangzhou 510640, China. Published Online:15 Sep 2016https://doi.org/10.1094/PDIS-04-16-0510-PDNAboutSections ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat The citrus psyllid (Diaphorina citri) is a small insect that feeds on the leaves and stems of citrus trees. It is also the only insect vector of Huanglongbing (HLB), the most devastating disease of the citrus industry in China. Controlling the citrus psyllid population density is an important safeguard measure against HLB, and biocontrol is the most effective method to control citrus psyllid in the future (Meyer et al. 2008). Citrus psyllid adults were collected into sterile centrifuge tubes from a citrus field, which had many diseased citrus trees infected HLB in Guangzhou, China, in 2015. The psyllids were placed directly on a potato dextrose agar (PDA) plate and incubated at 27°C with alternating light and dark for 2 to 3 days. Mycelium was picked into a new PDA culture plate, and the purification was repeated three times. Conidia were then suspended in sterile water for single-spore isolation. An isolate of an entomophagous fungus, GZMS-11, was isolated from citrus psyllid by the above method. GZMS-11 grew well on PDA, showed a round and fluffy colony, turning from white to brown with age. The colony diameter was 5.86 cm after 10 days at 27°C, with alternating light and dark. Brown pigment was produced and diffused into the medium after the colonies were cultured for 3 to 4 days. Conidiophores were erect and most of them were generated on the mycelium individually. Single phialide or multiple phialides were generated from the metulae, and they formed broom-like branches. The phialide size was 2.5 to 3.5 × 15 to 20 μm (avg. 3.0 ± 0.5 × 17.1 ± 1.5, n = 100), slender and acuminate, slightly curved, and the conidia attached with the phialide; the oval conidia size was 5.5 to 7.5 × 2.5 to 3.5 μm (avg. 6.2 ± 0.5 × 3.1 ± 0.5, n = 100). The cultural characteristics of the GZMS-11 was consistent with Paecilomyces variotii. Total DNA of GZMS-11 was extracted and the rDNA ITS region was sequenced by PCR using the universal primers ITS1 (5′-TCCGTAGGTGAACCTGCGG-3′, forward) and ITS4 (5′-TCCTCCGCTTATTGATATGC-3′, reverse). The PCR product showed a sequence identity of 97.0 to 99.0% with sequences of P. variotii strains (AY904061, FJ895878, JN798498, AY753335) reported in GenBank. Based on the biological characteristics and ITS sequence, isolate GZMS-11 was identified as a novel strain of P. variotii. The pathogenicity against citrus psyllid of GZMS-11 was tested by treating citrus psyllid adults with a conidial suspension at the concentration of 1.0 × 108 spores/ml (Gandarilla-Pacheco et al. 2013). The corrected mortality rates were 35.83, 66.71, and 97.16% after 3, 7, and 10 days, respectively. Two days after treatment, mycelium could be observed on the surface of some citrus psyllid through a stereoscopic microscope. After 7 days, spore production structure could be observed visually on the citrus psyllid. These results have indicated that GZMS-11 has strong pathogenicity against citrus psyllid adults, and has the potential for being used for biological control of citrus psyllid in the future.

The effect of toxicity of heavy metals contained in tailing sands on the organic carbon metabolic activity of soil microorganisms from different land use types in the karst region

To reveal the toxicity of multiple heavy metals from Pb–Zn tailing sands on soil microorganisms relating to soil organic C metabolic activity, 33 soil samples from different karst land use types (paddy field, corn field and citrus field) in Sidi village, Yangshuo, Guangxi, Southwest China were collected. The total concentrations of Pb, Zn, Cu and Cd, and diethylene triamine pentacetate acid (DTPA)-extractable Zn, Cu and Cd in the paddy field are higher than those in the corn and citrus field, which indicates that this area should not be used as farmland anymore according to the environmental quality evaluation standards for farmland of edible agricultural products of China (HJ/T332-2006). Due to the toxicity of multiple heavy metals from Pb–Zn tailing sands on soil microorganisms, the soil bacteria, actinomyces and fungi populations, soil microbial biomass C and N, and soil microbial quotient in the paddy field is lower than that in the corn and citrus field; however, soil organic C and total nitrogen (TN) in the paddy field are significantly higher than those in the citrus and corn field (p 0.05), which indicates that the above results have no relation to plant photosynthesis. The carbon source utilization of microbial samples using Biolog EcoPlate assay shows that the average well color development, Shannon–Wiener diversity index (H′ and E), Simpson index (D) and McIntosh index (U) in the paddy field are significantly lower than those in the citrus and corn fields (p < 0.05). Our results revealed that soil microorganisms under the effect of toxic heavy metals from Pb–Zn tailing sands can decrease the mineralization rate of soil organic C, which in turn produces the accumulation of soil organic C in the severe Pb–Zn tailing sand-contaminated area.

Prophage-mediated population dynamics of ‘Candidatus Liberibacter asiaticus’ in plant and insect hosts

As an intracellular bacterium, ‘Candidatus Liberibacter asiaticus’ (Las) lacks known transposons and IS elements but contains at least two prophages/phages. In this study, we revealed the genetic diversity and population dynamics of this bacterium based on two prophage hyper-variable regions (HVRs) using separate libraries constructed from citrus, periwinkle and psyllid. A total of 9 variants were identified, including 4 abundance types A, B, C, D and 5 rare types E, A1, A2, C1 and C2. The two HVRs, Type A and B, share highly conserved sequences and are localize to the two prophages, FP1 and FP2, respectively. The most abundant type in the psyllid library was Type A (36.71%), followed by Type B (25.17%) and Type C (19.72), but there was no Type D. However, the most abundant type in citrus was Type B (64.24%), followed by Type A (20.14%), C (11.11%) and D (1.39%). More interestingly, the Type A sequence was a very rare group (0.36%) in the periwinkle library. The most abundant type in the periwinkle library was Type B (43.73%) followed by Type C (39.07%) and then Type D (9.32%). Sequence analysis of these variants revealed the variations were due to the recombination and reassortment between two prophages. Conventional PCR results using primers specific to the different types indicated that Type A, B, C and D were present in more than 94.6% of higher titer Las-infected plant hosts; however, only 16.7% of tested psyllids contained D variants, which were very low titer, and Las-infected psyllids possessed higher titer Type A, B and C populations . Typing results for Las-infected citrus field samples indicated that only the Type D population was associated with huanglongbing (HLB) symptoms: high titer of D with typical blotchy mottle and extremely low to no type D with vein yellowing or other atypical HLB symptoms. Our finding that Las population dynamics derive from the prophage/phage activities may lead to a better understanding of how these bacteria evolve and adapt in different ecological niches.

Prophage-mediated dynamics of 'Candidatus Liberibacter asiaticus' populations, the destructive bacterial pathogens of citrus huanglongbing.

Prophages are highly dynamic components in the bacterial genome and play an important role in intraspecies variations. There are at least two prophages in the chromosomes of Candidatus Liberibacter asiaticus’ (Las) Floridian isolates. Las is both unculturable and the most prevalent species of Liberibacter pathogens that cause huanglongbing (HLB), a worldwide destructive disease of citrus. In this study, seven new prophage variants resulting from two hyper-variable regions were identified by screening clone libraries of infected citrus, periwinkle and psyllids. Among them, Types A and B share highly conserved sequences and localize within the two prophages, FP1 and FP2, respectively. Although Types B and C were abundant in all three libraries, Type A was much more abundant in the libraries from the Las-infected psyllids than from the Las-infected plants, and Type D was only identified in libraries from the infected host plants but not from the infected psyllids. Sequence analysis of these variants revealed that the variations may result from recombination and rearrangement events. Conventional PCR results using type-specific molecular markers indicated that A, B, C and D are the four most abundant types in Las-infected citrus and periwinkle. However, only three types, A, B and C are abundant in Las-infected psyllids. Typing results for Las-infected citrus field samples indicated that mixed populations of Las bacteria present in Floridian isolates, but only the Type D population was correlated with the blotchy mottle symptom. Extended cloning and sequencing of the Type D region revealed a third prophage/phage in the Las genome, which may derive from the recombination of FP1 and FP2. Dramatic variations in these prophage regions were also found among the global Las isolates. These results are the first to demonstrate the prophage/phage-mediated dynamics of Las populations in plant and insect hosts, and their correlation with insect transmission and disease development.

소규모 감귤원에서 네눈쑥가지나방 유충의 공간분포 특성에 대한 이해

본 연구는 네눈쑥가지나방 유충의 공간분포 특성을 분석하여 산란처와 관련된 유충의 감귤원 내로 정착과정을 이해하고자 실시하였다. 노지와 하우스 모두 감귤나무에서는 알이 발견되지 않았고, 부지화 시설재배 하우스의 방충망에서 발견되었다. 시설재배 부지화에서 네눈쑥가지나방 유충은 통계적으로 유의하게 집중분포를 보였다. 온주밀감 노지재배원에서 분산지수(ID)는 전체적으로 1.0내외로 약한 집중 정도를 나타냈다. 하지만, 검정통계량인 d-값은 대부분 조사일에 -1.96에서 1.96 사이에 있어 임의분포가 통계적으로 유의하였다. 집중정도를 나타내는 GI 지수는 전체적으로 낮아 집중정도가 약하였으며, 집중분포로 검정된 경우에도 집중정도는 크지 않았다. 네눈쑥가지나방 유충수의 빈도분포는 포아송(임의분포)과 음이항 분포(집중분포)를 동시 만족시키는 경우가 많았다. 또한 유충 공간분포의 시간적 변화는 초기 정착지점에서 분산하는 양상이 아니라 무작위로 외부로부터 비산하여 새로 정착되는 양상을 보였다. 기타 시설과 노지감귤원에서 네눈쑥가지나방 유충 공간분포 양상의 차이에 대하여 고찰하였다. This study was conducted to understand the settlement process of Ascotis selenaria larvae into citrus orchards with respect to oviposition site and analysis of the spatial distribution pattern of the larvae. A. selenaria eggs were not found on citrus trees in field and green house, but not on citrus trees in the field. A. selenaria larvae showed a significant clump distribution in the greenhouse. In the open citrus field, the index of dispersion was around 1.0 in most cases, with a weak clumping degree. However, the d-statistic was between -1.96 and 1.96, indicating a statistically significant random distribution. In addition, the Green's index (a clumping index) was very low in all cases, even though the clump distribution was accepted. for most samples, the probability distribution of larval frequency in the field satisfied the probability distribution functions of Poisson (random pattern) and the negative binomial (clump pattern) distribution. In addition, the temporal distribution of the larvae in the open field showed a pattern which was formed by colonizers from outside oviposition sites. Further, the difference in larval spatial distribution between field and greenhouse orchards was discussed.

Characterization of the microbial community structure in Candidatus Liberibacter asiaticus-infected citrus plants treated with antibiotics in the field.

BackgroundHuanglongbing (HLB) is a worldwide devastating disease of citrus. There are no effective control measures for this newly emerging but century-old disease. Previously, we reported a combination of Penicillin G and Streptomycin was effective in eliminating or suppressing the associated bacterium, ‘Candidatus Liberibacter asiaticus’ (Las).ResultsHere we report the bacterial composition and community structure in HLB-affected citrus plants during a growing season and while being treated with antibiotic combinations PS (Penicillin G and Streptomycin) and KO (Kasugamycin and Oxytetracycline) using the Phylochip™ G3 array. Both antibiotic treatments resulted in significantly lower Las bacterial titers (Pr<0.05) and hybridization scores. Of the 50,000+ available operational taxonomic units (OTUs) on PhyloChip™ G3, 7,028 known OTUs were present in citrus leaf midribs. These OTUs were from 58 phyla, of which five contained 100 or more OTUs, Proteobacteria (44.1%), Firmicutes (23.5%), Actinobacteria (12.4%), Bacteroidetes (6.6%) and Cyanobacteria (3.2%). In the antibiotic treated samples, the number of OTUs decreased to a total of 5,599. The over-all bacterial diversity decreased with the antibiotic treatments, as did the abundance of 11 OTUs within Proteobacteria, Firmicutes, Bacteroidetes and Planctomycetes. Within the Proteobacteria, ten OTUs representing the class γ-proteobacteria increased in abundance after four months of treatment, when the Las bacterium was at its lowest level in the HLB-affected citrus field plants.ConclusionsOur data revealed that Proteobacteria was constantly the dominant bacterial phylum recovered from citrus leaf midribs, with the α-proteobacterial and the γ-proteobacterial classes vying for prevalence. In addition, the level of bacterial diversity found in the leaf midribs of field citrus was greater than previously described. Bacterial cells in close proximity may be able to modify their microenvironment, making the composition of the microbial community an important factor in the ability of Las to cause HLB progression. A low Las level was seen as an annual fluctuation, part of the bacterial population dynamics, and as a response to the antibiotic treatments.

English

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Preliminary Observations on the Phytosanitary Status of the Croatian Satsuma Mandarin (Citrus unshiu Marc.) Collection

Preliminary surveys of citrus field trees in Croatia showed their unsatisfactory sanitary status especially with regard to the presence of Citrus tristeza virus (CTV) even though symptoms in the field are mostly absent. The highest CTV incidence was recorded in the Satsuma mandarin (Citrus unshiu Marc), commercially the most important citrus in the country. The Satsuma collection orchard was founded in the year 2005 at the Institute for Adriatic Crops and Karst Reclamation. It encompasses 12 mandarin cultivars and 51 Satsuma clones from different sources. With the aim of assessing the phytosanitary status of Satsuma collection, biological indexing of all 12 cultivars for principal virus and virus-like diseases was performed. Seven citrus bioindicators were used ; Mexican lime, Madame Vinous and Pineapple sweet oranges, Sicilian sour orange, CRC grapefruit, Troyer and Carrizo citranges. Herbaceous hosts (white sesame, red kidney bean and Chenopodium quinoa) were also used for cool-climate pathogen detection. Serological tests (ELISA and DTBIA) were performed for CTV and Citrus psorosis virus (CPsV) directly on 18 representative clones and on Mexican lime and Madame Vinous indicators. CPsV was not detected by serology while only 2 clones were CTV-negative, both in biological and laboratory tests. Furthermore, the most severe CTV strains displaying stem-pitting and seedling yellows in grapefruit and sweet oranges were found in 4 tested clones. No biological indication of other disease presence in the collection has been found so far. Further testing of the collection Satsumas is under way, as well as the sanitation of the most important cultivars.

Estabilidade da resistência de Brevipalpus phoenicis (Geijskes) (Acari: Tenuipalpidae) a hexythiazox em pomares de citros

The false spider mite, Brevipalpus phoenicis (Geijskes), is one the most important pests of the citrus groves and transmits the citrus leprosis virus. The acaricide hexythiazox has been widely used for controlling B. phoenicis in citrus groves. The resistance of this species to hexythiazox has already been detected at high frequencies at some locations. In order to implement a resistance management program, studies were undertaken to understand the stability of the resistance of B. phoenicis to hexythiazox by 1) comparing the life-history of susceptible (S) and resistant (R) strains under laboratory conditions, and 2) evaluating the dynamics of hexythiazox resistance in citrus field plots with low (< 20%) and high (> 60%) frequency of resistance, during two years. The frequencies of resistance were estimated with direct contact bioassays on eggs with discriminating concentration of 18 mg of hexythiazox/L of water. There were no significant differences between S and R strains, based on biological parameters evaluated to build fertility life tables. However, the resistance of B. phoenicis to hexythiazox was unstable under field conditions; that is, significant reductions in the frequency of resistance were observed in the absence of selection pressure, either in citrus field plots with low or high frequency of resistance. Therefore, the instability of B. phoenicis resistance to hexythiazox can be exploited in resistance management programs.