Sweet Orange Varieties Research Articles

PHYSICAL AND CHEMICAL PROPERTIES OF SWEET ORANGE GENOTYPES AVAILABLE IN BANGLADESH

Importance of fruits as valuable food resources, attention has been paid in recent years to study their physicochemical properties. Therefore, this investigation was undertaken to measure the physicochemical properties of the sweet orange genotype available in Bangladesh. A total of 8 genotypes including 3 released varieties (BAU Malta-1, BAU Malta-3, and BARI Malta-1) and 5 lines (CS Jain-001, CS Jain-002, CS Jain-003, CS Ram-001, and Variegated Malta) were included in this trial. Maximum average fruit weight (286.00 g), fruit size in terms of length (92.00 mm), and diameter (82.00 mm), mesocarp thickness (10.00 mm), and width of epicarp equatorial area (76.00 mm) was recorded from CS Jain-001 while the maximum number of segment (28.00), the diameter of fruit axis (23.66 mm), juice content (41.44%), titratable acidity (0.99%) and TSS: TA (33.73) was recorded from BAU Malta-3. TSS and juice pH was recorded maximum of 10.21% and 4.48, respectively in BAU Malta-1. Sugar content was found to be as follows, reducing sugar was the maximum in CS Jain-001 (3.50 %) while the highest total sugar (4.68%) was recorded in BAU Malta-1. Variegated Malta produced the maximum (48.45 mg/100 ml juice) ascorbic acid while CS Jain-001 contained maximum (8.35 mg/100 ml juice) ß-carotene. Therefore, considering fruit quality, BAU Malta-3, BARI Malta-1 can be used as fresh fruit. However, considering the fruit size, CS Jain-001 and CS Jain-002 could be used as breeding material to develop a new sweet orange variety with higher yield potential.

Tree growth, production and huanglongbing incidence of sweet orange varieties using different nursery tree standards

Insect-proof propagation of citrus is recommended to prevent vector-transmitted pathogens such as Candidatus Liberibacter spp. and Xylella fastidiosa. Although larger nursery trees were related to a superior post-planting performance in other perennial crops, there are few studies on citrus. This fact motivated us to evaluate the tree growth, the fruit production, and the huanglongbing (HLB) incidence of four commercial sweet orange varieties (‘Valencia Late’, ‘Hamlin’, ‘Pera’ and ‘Folha Murcha’) using two nursery tree standards (young whip and large headed trees). Eight years after planting, the tree size was similar between the evaluated treatments, especially for more vigorous varieties. However, large headed trees anticipated and increased the cumulative production by 30 % in average, which can improve the performance of reset trees in particular. Regardless the nursery tree standard and sweet orange variety, the cumulative incidence of HLB was relatively high over eight years. Therefore, a strict control of the vector should be reinforced in the field irrespectively of these factors.

Environmental requirements for infection of Colletotrichum acutatum and C. gloeosporioides sensu lato in citrus flowers and prevalence of these pathogens in Brazil

Citrus post-bloom fruit drop (PFD) is caused by Colletotrichum acutatum and C. gloeosporioides species complexes and frequently occurs in Sao Paulo (SP) state, Brazil. The environmental requirements for conidial germination and appressorium formation have been already determined in vitro; however, the environmental conditions for infection in citrus flowers remain unknown. C. acutatum is considered the main species complex causing PFD in citrus, but a survey of the pathogen’s prevalence has never been performed in SP state. The aims of this study were to assess the influence of different temperatures and wetness periods on infection of flowers by C. acutatum and C. gloeosporioides in potted citrus trees, and to determine the prevalence of both pathogens in different SP regions and sweet orange varieties. Environmental requirement trials were conducted in 2- to 3-year-old potted sweet orange trees. Flowers at different development stages (R2, R4 and R5) were inoculated with C. acutatum and C. gloeosporioides, and the trees were incubated at 18 or 24 °C for wetness periods of 6, 8, 12, 16 or 24 h. The percentages of inoculated flowers with PFD lesions and persistent calyces were calculated. The prevalence of both pathogens in SP regions was assessed in samples of diseased flowers collected at 16 commercial orchards of ‘Natal’, ‘Valencia’ and ‘Pera’ sweet oranges. The species complex was confirmed by isolation and PCR with species complex-specific primers. Blossom blight and persistent calyx incidences were higher in flowers inoculated with C. acutatum than in those inoculated with C. gloeosporioides. Incubation periods ranged from 2 to 5 days, and from 5 to 6 days for C. acutatum and C. gloeosporioides, respectively. In SP, irrespective of the region and sweet orange variety, C. acutatum was isolated from more than 80% of symptomatic flowers. We concluded that C. acutatum is not only more aggressive than C. gloeosporioides for causing PFD but also more prevalent in SP orchards.

Initial production and fruit quality of fifty-seven sweet orange varieties on four rootstocks in southern state of Bahia

Abstract Prior knowledge of scion/rootstock combinations is essential for establishing appropriate citrus orchard management strategies. The objective of this work was to assess the initial yield and fruit quality among 228 scion/rootstock combinations set up in the municipality of Ibirapuã, extreme south of the state of Bahia in 2015. Harvests were carried out from April to August 2019, when trees reached 4 years of age. Number, total mass and cross-sectional diameter of fruits, productive efficiency, pulp yield, soluble solids content, titratable acidity and SS/AT ratio were evaluated. Statistical difference for all characteristics related to production and fruit quality regarding factors studied and their combinations was observed. Among ‘Pera’ orange clones, ‘Pera CNPMF A-15’/‘San Diego’ citrandarin and ‘Pera CNPMF D-3’/‘Riverside’ citrandarin combinations stood out. ‘Sincorá’ orange, in combination with ‘San Diego’ and ‘Indio’ citrandarins presented potential to be recommended to producers who wish to anticipate their harvests, as well as ‘Natal Ipeal’ orange in combination with ‘Indio’ citrandarin, in the sense of postponing them.

Citrus Vascular Proteomics Highlights the Role of Peroxidases and Serine Proteases during Huanglongbing Disease Progression

Huanglongbing (HLB) is the most devastating and widespread citrus disease. All commercial citrus varieties are susceptible to the HLB-associated bacterium, Candidatus Liberibacter asiaticus (CLas), which resides in the phloem. The phloem is part of the plant vascular system and is involved in sugar transport. To investigate the plant response to CLas, we enriched for proteins surrounding the phloem in an HLB susceptible sweet orange variety, Washington navel (Citrus sinensis (L) Osbeck). Quantitative proteomics revealed global changes in the citrus proteome after CLas inoculation. Plant metabolism and translation were suppressed, whereas defense-related proteins such as peroxidases, proteases and protease inhibitors were induced in the vasculature. Transcript accumulation and enzymatic activity of plant peroxidases in CLas infected sweet orange varieties under greenhouse and field conditions were assessed. Although peroxidase transcript accumulation was induced in CLas infected sweet orange varieties, peroxidase enzymatic activity varied. Specific serine proteases were up-regulated in Washington navel in the presence of CLas based on quantitative proteomics. Subsequent activity-based protein profiling revealed increased activity of two serine proteases, and reduced activity of one protease in two C. sinensis sweet orange varieties under greenhouse and field conditions. The observations in the current study highlight global reprogramming of the citrus vascular proteome and differential regulation of enzyme classes in response to CLas infection. These results open an avenue for further investigation of diverse responses to HLB across different environmental conditions and citrus genotypes.

Studies on mutation breeding in citrus: Improving seedless types of ‘Kozan’ common orange by gamma irradiation

This study reports an induced physical mutation by gamma irradiation on a local sweet orange variety in order to develop new seedless varieties. Mature autumn shoots of seedy ‘Kozan’ common orange (Citrus sinensis (L.) Osb.) trees were irradiated with gamma rays from 60Co. The survival rate was 65 % for the dose of 60 Gy irradiation treatment of ‘Kozan’ common orange. In order to stabilize the mutation, mV3 plants were developed by re-budding and plants at mV3 generation were transplanted in the orchard in 2016. Observations in the present study were recorded for three consecutive years and trees which produced a sufficient number of fruits were evaluated for 19 fruit quality characters such as seed number, fruit diameter and maturity index. The seed number varied from 0 to 11, 0–10.82, and 0–10 per fruit in 2018, 2019 and 2020, respectively. Besides, high variations were observed in the mV3 population in terms of fruit weight and rind thickness. Through investigation of three years, two clones were completely seedless and selected as promising types. Vitamin C, total phenolic content and antioxidant activity in the fruit juice of the selected types were similar control. Furthermore, ploidy levels of the selections were investigated in order to explain the cause of seedlessness. Selected types were determined as diploid with the aid of flow cytometry. The selected lines were propagated in the field to confirm their stability and new commercial field trials have been conducted to evaluate the performances of the selections on different rootstocks.

Citrus Psorosis Virus: Current Insights on a Still Poorly Understood Ophiovirus.

Citrus psorosis was reported for the first time in Florida in 1896 and was confirmed as a graft-transmissible disease in 1934. Citrus psorosis virus (CPsV) is the presumed causal agent of this disease. It is considered as a type species of the genus Ophiovirus, within the family Aspiviridae. CPsV genome is a negative single-stranded RNA (-ssRNA) with three segments. It has a coat protein (CP) of 48 kDa and its particles are non-enveloped with naked filamentous nucleocapsids existing as either circular open structures or collapsed pseudo-linear forms. Numerous rapid and sensitive immuno-enzymatic and molecular-based detection methods specific to CPsV are available. CPsV occurrence in key citrus growing regions across the world has been spurred the establishment of the earliest eradication and virus-free budwood programs. Despite these efforts, CPsV remains a common and serious challenge in several countries and causes a range of symptoms depending on the isolate, the cultivar, and the environment. CPsV can be transmitted mechanically to some herbaceous hosts and back to citrus. Although CPsV was confirmed to be seedborne, the seed transmission is not efficient. CPsV natural spread has been increasing based on both CPsV surveys detection and specific CPsV symptoms monitoring. However, trials to ensure its transmission by a soil-inhabiting fungus and one aphid species have been unsuccessful. Psorosis disease control is achieved using CPsV-free buds for new plantations, launching budwood certification and indexing programs, and establishing a quarantine system for the introduction of new varieties. The use of natural resistance to control CPsV is very challenging. Transgenic resistance to at least some CPsV isolates is now possible in at least some sweet orange varieties and constitutes a promising biotechnological alternative to control CPsV. This paper provides an overview of the most remarkable achievements in CPsV research that could improve the understanding of the disease and lead the development of better control strategies.

Performance of early ripened varieties of ‘Sweet Orange’ in arid irrigated region of Punjab

Early maturing sweet orange varieties were evaluated during 2014–2018 and the data on leaf nutrient contents, growth, yield and fruit quality were analyzed. Leaf nutrient concentrations varied markedly among different varieties. Early Gold registered significantly higher canopy volume (34.4 m3) over other varieties (22.5–30.8 m3). Fruit yield was also significantly higher in Early Gold (42.3 kg/tree). In general, Early Gold showed overall superiority in term of juice content and quality characteristics over other tested sweet orange varieties, and hence has better perspectives in arid irrigated region of Punjab.

Hongos asociados con la muerte regresiva de los cítricos en Nuevo León y Tamaulipas, México


 El cultivo de cítricos es afectado por varios hongos fitopatógenos, los cuales pueden causar enfermedades y reducir su producción. El hongo Lasiodiplodia spp. causa muerte regresiva y otros síntomas en cítricos y en otros cultivos en diversos países, incluyendo México. El objetivo de este trabajo fue identificar cepas fúngicas aisladas de árboles de cítricos con síntomas de muerte regresiva y evaluar su patogenicidad en condiciones de invernadero. Los hongos aislados fueron identificados con base en sus características morfológicas como Lasiodiplodia theobromae, Fomitopsis meliae y Eutypella citricola, confirmados con la amplificación por PCR y secuenciación de la región ITS al comparar con las secuencias del GenBank. En el bioensayo de invernadero se comprobó que L. theobromae y F. meliae provocan síntomas de marchitez, muerte descendente y lesiones necróticas en las áreas inoculadas a partir del cuarto día posterior a la inoculación en plantas de naranjo dulce variedad Valencia. F. meliae + L. theobromae causaron daños más severos, provocando lesiones necróticas de 22 a 27 cm de longitud, marchitez y muerte regresiva y ambos fueron reaislados a partir de las lesiones producidas. E. citricola sólo produjo necrosis alrededor del área inoculada. De acuerdo con los resultados de la prueba de patogenicidad, los hongos L. theobromae y F. meliae causan muerte regresiva de los cítricos.

Limited persistence of residues and metabolites in fruit and juice following penicillin trunk infusion in citrus affected by Huanglongbing

The Florida citrus industry has suffered from Huanglongbing (HLB or citrus greening), a bacterial disease caused by Candidatus Liberibacter asiaticus (CLas), for almost 13 years with the citrus fruit production declining >70% between 2004 and 2017. With a sense of urgency, scientists with Florida Department of Agriculture and Consumer Services were tasked to seek a possible solution to mitigate the disease. Field trials (2014–16) were conducted to evaluate the effectiveness and environmental detectability of antibiotics used to combat HLB in experimental and commercial groves of Hamlin and Valencia varieties of sweet orange, and grapefruit. Across two year-long experiments, Penicillin G (PCN-G) was administered via trunk infusion into trees and subsequently detected in leaves, fruit and roots within 24 h. PCN-G started degrading 72 h post-infusion, with no detection at day 15 at or above 0.1 mg/L, the minimum level considered lethal to microbes. Reduction of CLas titer, as estimated by qPCR, was observed in treated trees when compared to control trees, and in many cases the rate of titer change over time was greater than that in control trees. Residue analysis of treated fruit for presence of PCN-G and two metabolites through UHPLC/MS confirmed that no PCN-G was present in fruit at harvest time, though metabolites were detected in low concentrations (<1 ppm). We suggest that PCN-G treatment of HLB infected citrus through a single trunk infusion at least 132 days prior to harvest may be a method for control of HLB with potentially minimal impacts on food safety and the environment, though further research will likely lead to improved methods.

Sweet Orange Fruit Age and Inoculum Concentration Affect the Expression of Citrus Black Spot Symptoms.

Citrus black spot (CBS), caused by Phyllosticta citricarpa, affects different citrus species worldwide. CBS is mainly expressed as false melanose and hard spot symptoms. There is no consensus in the literature about the period when fruit are susceptible to P. citricarpa infection and the length of the CBS incubation period. Therefore, this study aimed to assess the influence of sweet orange variety, fruit age, and inoculum concentration on the incubation period and the expression of different CBS symptoms. Attached fruit of Hamlin, Pera, and Valencia sweet orange at 1.5, 3.0, 5.0, and 7.0 cm diameter were inoculated with suspensions containing 103 and 105 conidia/ml of P. citricarpa. The percent conidial germination was quantified using scanning electron microscopy. The CBS symptoms on fruit were assessed monthly. The four diameters did not significantly affect conidial germination on the inoculated fruit, although CBS incidences were lower when larger fruit were inoculated. Hard spot symptoms on sweet orange fruit did not develop from the false melanose symptoms and vice versa. The incubation periods for false melanose were shorter than those observed for hard spot. False melanose began to appear 44 days after inoculation, but hard spot only formed at 113 days or later. Incubation periods were shorter and incidences of false melanose were higher following inoculation with higher inoculum concentration and smaller fruit diameter. The incubation period of hard spot varied among varieties and fruit diameters. However, there was no relationship between hard spot incidence and variety. This study provides a better understanding of the factors affecting the variation in the CBS incubation period and disease incidence on fruit.

Blond and blood juice supplementation in high fat diet fed mice: effect on antioxidant status and DDAH/ADMA pathway.

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disease spread throughout the world. The most frequent causes of death in NAFLD patients are due both to liver and cardiovascular damage. Several pathways, including the dimethylarginine dimethylaminohydrolase (DDAH)/asymmetric dimethylarginine (ADMA) pathway, are involved in the pathogenesis of NAFLD. It has been reported that ADMA plasmatic levels are increased in patients with hepatic dysfunction such as NAFLD. Although many studies demonstrated that some foods are effective in the treatment of NAFLD, few studies have evaluated their effects with respect to the prevention of the disease. It has been reported that sweet orange juice (OJ) consumption may be associated with potential health benefits. However, some varieties of sweet orange are more effective than others. The aim of the present paper was to investigate the effect of blond and blood sweet orange juice in prevention of NAFLD by evaluating its ability to improve liver steatosis in mice with diet-induced obesity, reducing oxidative stress and affecting the DDAH/ADMA pathway. Results obtained in our experimental conditions evidenced that blood orange juice rather than blond orange juice was more effective. Blood orange juice or blond orange juice enriched in anthocyanins may represent a promising dietary option for the prevention of fatty liver disease.

Network Analysis of Differentially Expressed Genes across Four Sweet Orange Varieties Reveals a Conserved Role of Gibberellin and Ethylene Responses and Transcriptional Regulation in Expanding Citrus Fruits

Citrus represents the most important non-climacteric fruits and thus understanding transcriptional control during fruit development is important for improving fruit yield and quality. Compared to relatively intensive transcriptomic studies of ripening citrus fruits, much less is known regarding expanding fruits. To provide a systems view of hormone response and transcriptional regulation in citrus fruit development from Stage I (slow fruit growth) to Stage II (rapid growth), we re-analyzed the fruit transcriptomes which we previously collected from the sweet orange varieties, Newhall, Xinhui, Bingtang, and Succari (Citrus sinensis L. Osbeck). A total of 3145 genes were differentially expressed across all four varieties, indicating that they likely have conserved functions in orange fruit development. Using a gene coexpression network-based systems approach, we constructed the subnetworks respectively for gibberellin response, ethylene response, transcription factors and chromatin modifications. Analysis of these subnetworks has led to the identification of more than a dozen major hub genes, such as EXPA1, GASA1/14, ERF13, HB22, ATK1, and TOPII, which represent the most promising candidates for future functional characterization.

Initial performance of alternative citrus scion and rootstock combinations on the northern coast of the state of Bahia, Brazil

Abstract The diversification of scion and rootstock varieties is tremendously necessary for the citrus industry in Northeastern Brazil. The initial performance of 13 sweet orange varieties grafted onto ‘San Diego’ citrandarin, and of ‘Cara-Cara’ navel orange and ‘CNPMF-02 Persian’ lime grafted onto several rootstocks was evaluated in the municipality of Inhambupe, northern coast of the state of Bahia. Three trials were carried out separately, and tree size, fruit production and quality were assessed in the first three crops, with planting in 2008 at 6.0 m x 3.0 m spacing with supplemental irrigation. ‘Aquiri’, ‘Biondo’, ‘Agridoce’, ‘Kona’, ‘Pineapple’, ‘Russas CNPMF-03’ and ‘Salustiana’ sweet oranges showed the largest cumulative production in the first three crops. ‘Pera CNPMF D-6’, ‘Westin CNPMF’ and ‘Salustiana’ sweet oranges had fewer seeds per fruit, being more appropriate for fresh fruit market, in addition to greater production efficiency for the first one. Although ‘Westin CNPMF’ has shown good fruit quality, its initial production was low. ‘Florida’ rough lemon and ‘Volkamer’ lemon induced higher cumulative production compared to ‘Cara Cara’ navel orange, but tree size and fruit quality were not influenced by any evaluated rootstock. ‘Cleopatra’ mandarin and ‘Riverside’ citrandarin led to higher tree size and cumulative production and heavier fruits of ‘CNPMF-02 Persian’ lime. All scion and rootstock combinations have potential for cultivation on the northern coast of the state of Bahia and appear as an alternative to the prevalent ‘Pera’ sweet orange on ‘Rangpur’ lime combination.

FACTORS AFFECTING PHENOLOGY OF DIFFERENT Citrus VARIETIES UNDER THE TEMPERATE CLIMATE CONDITIONS OF SANTA FE, ARGENTINA

ABSTRACT The aim of this study was to characterize the phenology of different sweet orange, tangerines and tangerine hybrid varieties growing under the temperate climate conditions of Santa Fe Province, Argentina. Phenological stages were observed weekly during five consecutive years using a BBCH (Biologische Bundesanstalt, Bundessortenamt and Chemical industry) scale adapted for Citrus trees. All varieties showed a winter rest period from June to August. ‘New Hall’ and ‘Navelina’ varieties were the first to reach sprouting stage, whereas ‘Okitsu’ was the last. Inception of flowering occurred from August 13th to September 6th; and full bloom from September 12th to October 2nd. Fruit harvest started with the ‘Okitsu’ cultivar in March, and continued over a 7-month period. Interannual variation for inception of sprouting was high (44 days), and sprouting was correlated with both thermal accumulation (above 13ºC) and the amount of solar radiation measured during July (p&lt;0.0001; r2=0.79). Navel oranges and the ‘Murcott’ hybrid bloomed 5–15 days earlier than other varieties, increasing probability of damage by late frosts.

Gene coexpression network analysis of fruit transcriptomes uncovers a possible mechanistically distinct class of sugar/acid ratio-associated genes in sweet orange

BackgroundThe ratio of sugars to organic acids, two of the major metabolites in fleshy fruits, has been considered the most important contributor to fruit sweetness. Although accumulation of sugars and acids have been extensively studied, whether plants evolve a mechanism to maintain, sense or respond to the fruit sugar/acid ratio remains a mystery. In a prior study, we used an integrated systems biology tool to identify a group of 39 acid-associated genes from the fruit transcriptomes in four sweet orange varieties (Citrus sinensis L. Osbeck) with varying fruit acidity, Succari (acidless), Bingtang (low acid), and Newhall and Xinhui (normal acid).ResultsWe reanalyzed the prior sweet orange fruit transcriptome data, leading to the identification of 72 genes highly correlated with the fruit sugar/acid ratio. The majority of these sugar/acid ratio-related genes are predicted to be involved in regulatory functions such as transport, signaling and transcription or encode enzymes involved in metabolism. Surprisingly, only three of these sugar/acid ratio-correlated genes are weakly correlated with sugar level and none of them overlaps with the acid-associated genes. Weighted Gene Coexpression Network Analysis (WGCNA) has revealed that these genes belong to four modules, Blue, Grey, Brown and Turquoise, with the former two modules being unique to the sugar/acid ratio control.ConclusionOur results indicate that orange fruits contain a possible mechanistically distinct class of genes that may potentially be involved in maintaining fruit sugar/acid ratios and/or responding to the cellular sugar/acid ratio status. Therefore, our analysis of orange transcriptomes provides an intriguing insight into the potentially novel genetic or molecular mechanisms controlling the sugar/acid ratio in fruits.

Laranjeiras mediterrâneas de meia-estação em condições de sequeiro em clima subtropical no Brasil

‘Pera’ is one of the major sweet orange commercial varieties and it is the only one being harvested in the mid-season in Brazil. Similar or superior mid-season cultivars could improve the gains in the juice processing chain. In this work, we evaluated 29 sweet orange selections introduced in Brazil from Mediterranean countries. Several sweet orange varieties were evaluated in two distinct experiments. In both trials, the rootstock was Sunki mandarin and the experimental design was in randomized blocks, with three replications and two trees in the unit. The experimental plots were planted on May 2001 in Bebedouro, northern Sao Paulo State, Brazil, in an oxisol under rain-fed cultivation in subtropical climate. Collected data included tree growth, yield, and physical and chemical fruit traits from 2005 thru 2008. ‘Do Tua Grauda’/146, ‘Do Tua Sr. Mamede’/148, ‘Do Tua’/149, ‘Do Tua’/160, ‘Do Tua’/176, ‘Convento’/155, ‘Grada’/158, ‘De Setubal’/174, ‘De Setubal’/180, ‘Pera da Vidigueira Sr. Antunes’/159, ‘Sanguinea’/144, Amares’/150, ‘Prata da Ponte’/151, ‘Prata Lima’/152, ‘Pala’/153, ‘Portela’/154, ‘Evora’/157, ‘De Vale dos Besteiros’/161, ‘Biondo Corigliano/164’, ‘Vera’/166, ‘Entrefina’/168, ‘De Vale dos Besteiros’/175, ‘Laranja R.A.H.’/177 and ‘Maca’/182 are suitable for rain-fed cultivation in a subtropical region of Brazil, aiming to juice processing. ‘Pardilho’/169 could be used for fresh market because it is a navel orange.

&lt;b&gt;Modeling the incidence of citrus canker in leaves of the sweet orange variety ‘Pera’

Citrus canker, caused by the bacterium Xanthomonas citri subsp. citri , is one of the most important diseases of citrus. The use of resistant genotypes plays an important role in the management and control of the disease and is the most environmentally sustainable approach to disease control. Citrus canker incidence was recorded in an experiment on nine genotypes of the sweet orange variety ‘Pera’ grafted on four rootstocks. The experiment was started in 2010 and the incidence of citrus canker on the leaves was recorded on a quarterly basis. The incidence data from the experiment were analyzed using a zero-inflated Beta regression model (RBIZ), which is the appropriate method to describe data with large numbers of zeros. Based on the residual analysis, the data fit the model well. The discrete component of the explanatory variable, rootstock, was not significant as a factor affecting the onset of disease, in contrast with the continuous component, genotype, which was significant in explaining the incidence of citrus canker.

Frequency response of late-season ‘Valencia’ orange to selective harvesting by vibration for juice industry

Citrus mechanical harvesting has been investigated since the 1960's. Even though mechanical harvesting could significantly lower production costs, the implementation by the private sector has been slow. The current harvesting technologies detach the fruits with trunk, canopy or branch vibration. For late-season sweet orange varieties which simultaneously bear mature fruit, immature fruitlets and flowers, shaker harvesting decreases the subsequent year's yield. This study, investigated the frequency response of mature fruits and immature fruitlets to determine the optimum frequency range for an efficient and selective harvest. Laboratory vibration transmission tests were conducted with 14 branches bearing 76 mature fruits and 151 immature ‘Valencia’ fruitlets. The fruit and branch response to the forced vibration was measured by several sets of five triaxial accelerometers with a dynamic signal analyser. Three frequency ranges with the highest vibration transmission values were identified for mechanical harvesting lower than 10 Hz. The first frequency range (1.5–2.5 Hz) corresponded best with the most efficient vibration transmission, involving more than 90% of fruit. The second frequency range (4.5–5 Hz) successfully discriminated between mature fruit and immature fruitlets. In this frequency range, 53.4% of mature fruit amplified the acceleration a mean value of 2.2 times, while only 7.3% of immature fruitlets amplified the acceleration with a mean value of 4.4 times. The third frequency range (7–8 Hz) had the lowest vibration transmission value. The frequency response of mature citrus fruits, and their markedly higher fruit mass, were significant factors in efficient selective mechanical harvesting.

Reação de híbridos de citros à inoculação com Alternaria alternata

RESUMO A mancha marrom de alternária (MMA), causada por Alternaria alternata, que produz uma toxina específica ao hospedeiro (Host Specific Toxin – HST) é uma doença de grande importância nos pomares de tangerinas no mundo. A doença afeta tangerinas, alguns de seus híbridos interespecíficos e pomelos, sendo que no Brasil, as principais variedades plantadas, a tangerina Ponkan e o tangor Murcott, são altamente suscetíveis ao fungo, que também é saprofítico alternativo, se reproduz nos pomares, sendo seus esporos facilmente disseminados pelo vento. Para esse trabalho, foram selecionados híbridos de citros, obtidos por cruzamentos dirigidos, por apresentarem características agronômicas que os tornam potenciais novas variedades de laranjas e tangerinas, tanto para a citricultura industrial, quanto de mesa. Esses híbridos foram avaliados quanto à resposta à MMA por meio da inoculação com A. alternata in vitro e in vivo, uma etapa imprescindível para a liberação de novas variedades. Foram selecionados mais de trinta genótipos resistentes ou que apresentaram poucos sintomas da doença. A seleção de variedades resistentes à doença é de grande importância econômica, pois além de diminuir os custos de produção, aumentados sobremaneira com a utilização do controle químico, contribui para a diminuição de inóculo no campo.