Advances in Citrus Breeding, Genetics, Physiology and Horticultural Management

A special issue of Agronomy (ISSN 2073-4395). This special issue belongs to the section "Horticultural and Floricultural Crops".

Deadline for manuscript submissions: closed (31 October 2021) | Viewed by 22069

Special Issue Editors

CREA, Research Centre for Olive, Fruit and Citrus Crops, Corso Savoia 190, 95024 Acireale, Italy
Interests: scion and rootstock breeding; marker-assisted selection; phenotyping for biotic and abiotic stress resistance; germplasm management and utilization
Instituto Valenciano de Investigaciones Agrarias (IVIA), Centro de Citricultura y Producción Vegetal, Carretera CV-315 Km. 10,7, 46113 Moncada (Valencia), Spain
Interests: culture tissue; flow cytometry; molecular markers; polyploidy; genetics; breeding; reproductive biology
National Agricultural Research Institute, Andes 1365, 11100 Montevideo, Uruguay
Interests: plant breeding and biotechnology; plant physiology; plant reproduction; oxidative stress; horticultural management

Special Issue Information

Dear Colleagues,

Citrus is cultivated in many tropical and subtropical regions and is one of the most important fruit tree  crops in the world. Over the last few decades, the citrus industry has experienced a dramatic change. It is trying to fulfill new market requirements and is facing major threats related to the occurrence of existing and emerging diseases. Conventional and novel research approaches to scion and rootstock improvement and orchard management are being adopted to lead to long-term sustainable citrus production.

The aim of this Special Issue is to highlight recent advances in fundamental and applied research in the fields of citrus breeding, genetics, genomics, physiology, and field management leading to improved productivity and fruit quality. We welcome novel research articles and reviews on: (1) scion and rootstock breeding though conventional and biotechnological approaches; (2) mapping and identification of QTLs and development of new protocols for marker-assisted selection; (3) germplasm characterization and exploitation for the introgression of useful traits into cultivated varieties; (4) new phenotyping protocols for biotic and abiotic stresses; (5) omics approaches to understanding biological processes of horticultural relevance; and (6) ecophysiological studies concerning the adaptation of citrus cultivars to diverse environments and climate change.

Manuscripts regarding current trends in cultivation practices, such as high-density plantings, evaluation of new citrus rootstocks and scions, undercover production systems, and deficit irrigation strategies, will be also considered for publication in this Special Issue.

Dr. Marco Caruso
Dr. Pablo Aleza
Dr. Fernando Rivas
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Agronomy is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • citrus breeding
  • marker-assisted selection
  • genomics
  • biotechnology
  • phenotyping
  • scion/rootstock interaction
  • germplasm
  • biotic and abiotic stresses
  • fruit quality
  • orchard management

Published Papers (8 papers)

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Research

14 pages, 16489 KiB  
Article
Flavonoids and Limonoids Profiles Variation in Leaves from Mandarin Cultivars and Its Relationship with Alternate Bearing
by Cecilia Rodríguez Ceraolo, Valeria Vázquez, Ignacio Migues, María Verónica Cesio, Fernando Rivas and Horacio Heinzen
Agronomy 2022, 12(1), 121; https://0-doi-org.brum.beds.ac.uk/10.3390/agronomy12010121 - 04 Jan 2022
Cited by 3 | Viewed by 1704
Abstract
Alternate bearing in citrus trees has been extensively studied as a key feature for citrus growers. Although the genetic and the biochemical process occurring during alternate bearing has been studied extensively, there is a lack of information identifying the presence of metabolic indicators [...] Read more.
Alternate bearing in citrus trees has been extensively studied as a key feature for citrus growers. Although the genetic and the biochemical process occurring during alternate bearing has been studied extensively, there is a lack of information identifying the presence of metabolic indicators during “on” and “off” years. In citrus plants, leaves play a central role in the metabolic pathway triggering the flowering induction process. To investigate the changes during this transition, a liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) analysis of the leaf profiles of 20 compounds (17 polyphenols, two limonoids, and one furanocoumarin), in bearing and non-bearing branches arising from four different mandarin genotypes, was performed. The same metabolites were found in all the genotypes at both stages: both limonoids and 11 polyphenols. Using these compounds, the chemotaxonomic differentiation between cultivars was assessed. The levels of flavanones and limonoids showed differences in both bearing stages and the transition from vegetative to flowering could be shown by the activation of the polyphenol biosynthetic pathway, from precursors like naringenin to metabolic end-points such as narirutin and polymethoxyflavones. Narirutin levels showed significant differences between both stages, suggesting it as a possible marker of the physiological status of the branch. Full article
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33 pages, 5795 KiB  
Article
The Perfect Match: Adjusting High Tree Density to Rootstock Vigor for Improving Cropping and Land Use Efficiency of Sweet Orange
by Eduardo Augusto Girardi, João Gabriel Panegossi Sola, Marcelo da Silva Scapin, Alécio Souza Moreira, Renato Beozzo Bassanezi, Antonio Juliano Ayres and Leandro Peña
Agronomy 2021, 11(12), 2569; https://0-doi-org.brum.beds.ac.uk/10.3390/agronomy11122569 - 17 Dec 2021
Cited by 6 | Viewed by 3226
Abstract
The rise in the productivity of sweet orange in Brazil has been related to the use of superior rootstocks and higher tree density, among other factors. In order to investigate whether the cropping system and the land use efficiency would benefit from more [...] Read more.
The rise in the productivity of sweet orange in Brazil has been related to the use of superior rootstocks and higher tree density, among other factors. In order to investigate whether the cropping system and the land use efficiency would benefit from more intensive cultivation, the performance of Valencia sweet orange was evaluated over nine years on four rootstocks, which induced contrasting vigor, at 513, 696 and 1000 trees·ha−1. Agronomic Institute of Campinas (IAC) 1697 and IAC 1710 citrandarins, and diploid and allotetraploid (4×) Swingle citrumelos were classified as semi-dwarfing, super-standard, standard, and dwarfing rootstocks, respectively. The fruit yield per tree was decreased at higher tree densities, notably for more vigorous rootstocks. Conversely, the cumulative productivity was increased over the evaluation period by 27% at 1000 trees·ha−1, irrespective of the rootstock, and the most vigorous rootstock resulted in 2.5 times higher production than the dwarfing one on average. Most fruit quality parameters were seldom influenced by the tree density, while the rootstock was a decisive factor in improving the quality and the soluble solids content. Dwarfing rootstocks allowed for harvesting 17% more fruit per minute by manual pickers. Because the tree row volume per area is lower with such rootstocks, even at higher tree density, spray volume can be reduced, although appropriate equipment should be developed for better spray coverage on smaller trees. Nine years after planting under strict vector control, the cumulative incidence of huanglongbing-symptomatic trees on IAC 1710 was double that on Swingle 4×. Taken together, the results suggested that the land use efficiency in the citrus industry can be further improved by planting vigorous rootstocks at moderate to high tree densities. Nevertheless, obtaining highly productive semi-dwarfing and dwarfing rootstocks is the sine qua non for making high-density pedestrian sweet orange orchards more profitable. Full article
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17 pages, 3269 KiB  
Article
Tree Growth and Production of Rainfed Valencia Sweet Orange Grafted onto Trifoliate Orange Hybrid Rootstocks under Aw Climate
by Eduardo Augusto Girardi, Antonio Juliano Ayres, Luiz Fernando Girotto and Leandro Peña
Agronomy 2021, 11(12), 2533; https://0-doi-org.brum.beds.ac.uk/10.3390/agronomy11122533 - 13 Dec 2021
Cited by 2 | Viewed by 2251
Abstract
Brazil is the largest producer of sweet orange and its juice in the world. Extensive cultivated area is located under an Aw climate in the North–Northwest of the state of São Paulo and the Triângulo of Minas Gerais state, being subjected to severe [...] Read more.
Brazil is the largest producer of sweet orange and its juice in the world. Extensive cultivated area is located under an Aw climate in the North–Northwest of the state of São Paulo and the Triângulo of Minas Gerais state, being subjected to severe drought events. Although 56% of the orchards are irrigated in these regions, there is a need for drought tolerant rootstocks as an alternative to traditional genotypes such as Rangpur lime and Volkamer lemon, which are susceptible to the endemic citrus sudden death disease (CSD). In this sense, the tree size and production of Valencia sweet orange grafted onto 23 rootstock genotypes were evaluated over a ten-year period in rainfed cultivation at 7.0 m × 3.0 m spacing. Most evaluated types resulted from the cross of Poncirus trifoliata with Citrus, but two interspecific hybrids of Citrus (Sunki mandarin × Rangpur lime hybrids), the Barnes trifoliate orange and a tetraploid selection of Swingle citrumelo were also tested. Tropical Sunki mandarin was used as the reference control. Those hybrids coming from the cross of Sunki × Flying Dragon induced large tree sizes to Valencia sweet orange as well as the other citrandarins, Tropical Sunki mandarin and the Sunki mandarin × Rangpur lime hybrids, whereas only the tetraploid Swingle citrumelo behaved as a dwarfing rootstock, decreasing the canopy volume by 77% compared to that induced by the most vigorous citrandarin 535. The citrandarins 543 and 602 and the citrange C38 induced the highest mean fruit production, 67.2 kg·tree−1, but they also caused pronounced alternate bearing and only the hybrid 543 led to a high production efficiency consistently. Graft incompatibility symptoms were not observed over the evaluation period, and the canopy shape of Valencia sweet orange was also influenced by the rootstocks tested. Two citrandarins and one citrange were selected as the most promising alternative rootstocks for Valencia sweet orange grown under an Aw climate, even though productivity would likely benefit from supplementary irrigation. Full article
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13 pages, 1052 KiB  
Article
Evaluation of Three New Citrus Rootstocks under Boron Toxicity Conditions
by Lidia Aparicio-Durán, Frederick G. Gmitter, Jr., Juan M. Arjona-López, Jude W. Grosser, Rocío Calero-Velázquez, Áurea Hervalejo and Francisco J. Arenas-Arenas
Agronomy 2021, 11(12), 2490; https://0-doi-org.brum.beds.ac.uk/10.3390/agronomy11122490 - 08 Dec 2021
Cited by 5 | Viewed by 2371
Abstract
Boron (B) toxicity is a common limiting factor both in arid and semiarid regions, such as the Mediterranean Basin. Citrus trees are sensitive to B-toxicity, which generates a negative impact in citrus orchards. In this work, two promising citrus rootstocks (UFR-6 and 2247 [...] Read more.
Boron (B) toxicity is a common limiting factor both in arid and semiarid regions, such as the Mediterranean Basin. Citrus trees are sensitive to B-toxicity, which generates a negative impact in citrus orchards. In this work, two promising citrus rootstocks (UFR-6 and 2247 x 6070-02-2) have been assessed against B-toxicity and compared with Carrizo citrange, a common commercial citrus rootstock in Mediterranean Basin. Three B concentration treatments (Control, 1 and 2.5 mM H3BO3) were established, irrigating the plants three times per week for 21 days under greenhouse conditions. During the assay, above-ground symptoms, and chlorophyll index (SPAD) were recorded. At the end of the experiment, stomatal conductance, relative water content, and B concentration in leaves and roots were determined. The increasing B concentration in plants generates visual damage in leaves for all citrus rootstocks assayed. Carrizo citrange displayed the greatest visual symptoms, decreased its chlorophyll index (SPAD), and stomatal conductance throughout the B-treatment. However, UFR-6 and 2247 x 6070-02-2 displayed less symptoms than Carrizo citrange and only reduced its parameters under the 2.5 mM H3BO3 treatment. These results can aid citrus grower rootstock planting decisions with under B-toxicity conditions. Full article
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18 pages, 2663 KiB  
Article
Parthenocarpy and Self-Incompatibility in Mandarins
by Rafael Montalt, María Carmen Vives, Luis Navarro, Patrick Ollitrault and Pablo Aleza
Agronomy 2021, 11(10), 2023; https://0-doi-org.brum.beds.ac.uk/10.3390/agronomy11102023 - 09 Oct 2021
Cited by 13 | Viewed by 2841
Abstract
Citrus reproductive biology is complex. One of its characteristic features is parthenocarpy that enables seedless fruit production. Citrus parthenocarpy and self-incompatibility knowledge is only partial and sometimes discrepant. Increasing such knowledge is relevant for better managing cultivated varieties and improving the selection of [...] Read more.
Citrus reproductive biology is complex. One of its characteristic features is parthenocarpy that enables seedless fruit production. Citrus parthenocarpy and self-incompatibility knowledge is only partial and sometimes discrepant. Increasing such knowledge is relevant for better managing cultivated varieties and improving the selection of parents in breeding strategies to recover seedless varieties such as mandarins. This work develops an efficient protocol to characterize self-incompatibility and different parthenocarpy types based on emasculation, hand self-pollination, and hand cross-pollination. It analyzes fruit setting and seed production coupled with histological pollen performance observations. We analyzed the reproductive behavior of nine mandarin varieties with relevant characteristics as parents for seedless mandarin breeding. ‘Clemenules’ clementine and ‘Moncada’ mandarins were strictly self-incompatible with facultative and vegetative parthenocarpy; ‘Imperial’ mandarin and ‘Ellendale’ tangor displayed no strict self-incompatibility associated with facultative and vegetative parthenocarpy; ‘Fortune’ mandarin was self-incompatible with facultative and stimulative parthenocarpy; ‘Campeona’ and ‘Salteñita’ mandarins were self-compatible with vegetative parthenocarpy; ‘Serafines’ satsuma was associated with male sterility together with facultative and vegetative parthenocarpy; and ‘Monreal’ clementine was self-compatible and nonparthenocarpic. Our protocol can be applied for screening of mandarin germplasm and to characterize new parents. Reproductive behavior knowledge is important for optimizing seedless mandarin breeding programs based on diploidy, triploidy, or induced mutagenesis. Full article
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15 pages, 1384 KiB  
Article
Selection of New Late-Season Mandarin Cultivars Based on Sensory Changes and Consumer Acceptance after Fruit Cold Storage
by Paula Tarancón, Adrián Giménez-Sanchis, Pablo Aleza and Cristina Besada
Agronomy 2021, 11(1), 116; https://0-doi-org.brum.beds.ac.uk/10.3390/agronomy11010116 - 09 Jan 2021
Cited by 10 | Viewed by 2251
Abstract
Late-season mandarins are normally cold-stored to prolong the commercial season. Thus, it is necessary to investigate poststorage consumer acceptance to predict the potential success of new late-season mandarin varieties on the market. The aim of the present work was to evaluate consumer response [...] Read more.
Late-season mandarins are normally cold-stored to prolong the commercial season. Thus, it is necessary to investigate poststorage consumer acceptance to predict the potential success of new late-season mandarin varieties on the market. The aim of the present work was to evaluate consumer response to three new late-season cultivars preselected in the IVIA breeding programme (Omet, Matiz and Tri-703) after different cold storage periods. The three new cultivars were compared to commercial cultivars Orri, Nadorcott and Ortanique, all of which are widely available in stores. A multidisciplinary approach was used to determine the main changes during storage at 1 °C for up to one month: (1) analysis of physico-chemical parameters; (2) description of the sensory profile by semitrained assessors by the Free Choice Profile technique; (3) evaluation of consumer acceptability and purchase intention. Our results showed that the sensory changes that fruit underwent during storage depended on the variety; these changes allowed us to understand why consumer preferences varied during storage. Of the three new cultivars, two (Omet and Tri-703) showed the greatest potential for success. However, while Tri-703 can be stored for one month, Omet should not be stored longer than 15 days due to its susceptibility to manifest skin damage during storage. Of the commercial cultivars, internal Orri quality was keenly appreciated by consumers, while Ortanique was considered the most attractive variety. The multidisciplinary approach followed in this study proved to be a potent tool for selecting varieties that should be implemented in selection processes of breeding programmes. Full article
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24 pages, 3861 KiB  
Article
Intermediate Inheritance with Disomic Tendency in Tetraploid Intergeneric Citrus × Poncirus Hybrids Enhances the Efficiency of Citrus Rootstock Breeding
by Leny Calvez, Alexis Dereeper, Pierre Mournet, Yann Froelicher, Saturnin Bruyère, Raphaël Morillon and Patrick Ollitrault
Agronomy 2020, 10(12), 1961; https://0-doi-org.brum.beds.ac.uk/10.3390/agronomy10121961 - 13 Dec 2020
Cited by 8 | Viewed by 2994
Abstract
Rootstocks are crucial for the sustainability of the citrus industry worldwide. Diploid intergeneric Citrus × Poncirus hybrids have contributed considerably to citrus rootstock improvement and their tetraploid (doubled-diploid) forms are important resources for the creation of a new generation of tetraploid rootstocks. To [...] Read more.
Rootstocks are crucial for the sustainability of the citrus industry worldwide. Diploid intergeneric Citrus × Poncirus hybrids have contributed considerably to citrus rootstock improvement and their tetraploid (doubled-diploid) forms are important resources for the creation of a new generation of tetraploid rootstocks. To optimize the efficiency of tetraploid rootstock breeding strategies, more knowledge is required on inheritance in the allotetraploid genitors. A set of 159 new SNP markers that fully distinguish Poncirus trifoliata (L.) Raf. from Citrus species was developed from polymorphisms mined in GBS data and used to establish a genetic map of tetraploid citrumelo (C. × paradisi Macfad. × P. trifoliata) and to analyze the meiotic behavior of tetraploid citrumelo and citrandarin (C. reticulata Blanco × P. trifoliata). The tetraploid citrumelo genetic map was highly syntenic and collinear with the clementine reference genome. The apparent intergeneric recombination rate was strongly limited by high preferential chromosome pairing, resulting in intermediate inheritance with disomic tendency. Such inheritance, also observed in tetraploid citrandarin, results in the transmission by the diploid gametes of a high rate of intergeneric heterozygosity. It is therefore expected that a large part of the genetic value selected in the original diploid intergeneric rootstock is transmitted to the tetraploid sexual progenies. Full article
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19 pages, 2369 KiB  
Article
Identification of Field Tolerance and Resistance to Mal Secco Disease in a Citrus Germplasm Collection in Sicily
by Riccardo Russo, Marco Caruso, Carmen Arlotta, Angela Roberta Lo Piero, Elisabetta Nicolosi and Silvia Di Silvestro
Agronomy 2020, 10(11), 1806; https://0-doi-org.brum.beds.ac.uk/10.3390/agronomy10111806 - 17 Nov 2020
Cited by 12 | Viewed by 3148
Abstract
Mal secco is a tracheomycotic disease caused by the fungus Plenodomus tracheiphilus (Petri) Gruyter, Aveskamp, and Verkley that has caused severe damage and loss of yield in the citrus industry in the Mediterranean area, for 100 years. While the disease can affect different [...] Read more.
Mal secco is a tracheomycotic disease caused by the fungus Plenodomus tracheiphilus (Petri) Gruyter, Aveskamp, and Verkley that has caused severe damage and loss of yield in the citrus industry in the Mediterranean area, for 100 years. While the disease can affect different cultivated citrus species, lemon (C. × limon var. limon (L.) Burm. f.) and citron are the most susceptible. The identification of resistant or field-tolerant clones and hybrids is a major goal for lemon growers and breeders. To identify sources of resistance or tolerance to the disease, we performed a phenotypic survey on a lemon and lemon-like open-field germplasm planted at CREA (Research Centre for Olive, Fruit and Citrus Crops), Italy, in an area with high pathogen pressure. Phenotyping was performed visually, four times, for three consecutive years, on a total of 50 accessions, with two or three replicate trees per accession. Moreover, molecular screening based on real-time PCR was performed, for two consecutive years, on twigs, young leaves, and mature leaves of all plants, to detect the pathogen in the absence of clear symptoms. The accessions were categorized into seven groups based on the presence of visual symptoms, real-time PCR pathogen detection, and canopy volume. The results revealed sources of tolerance in lemon and citron hybrids. The molecular screening identified P. tracheiphilus in all lemon clones, with mean Ct values ranging from 17 to 39. The screening also identified P. tracheiphilus in clones without clear symptoms, indicating their ability to tolerate the disease. Moreover, a strong negative correlation was found between the Ct values in twigs and symptom severity (r = −0.72). This indicates that the DNA from twigs is the most appropriate for use in performing reliable phenotyping of mal secco susceptibility in adult plants. An autotetraploid lemon (Doppio Lentini) seems to be immune to the disease, under natural pressure, since P. tracheiphilus was not detected by real-time PCR and visual screening. Overall, the data obtained are a valuable resource for identifying both the most tolerant lemon varieties suitable for areas with high pathogen pressure and the best breeding parents for the introgression of resistance genes into lemon genotypes. Full article
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