Nursery performance of potentially promising rootstocks for citriculture in the south of Brazil / Desempenho em viveiro de porta-enxertos potencialmente promissores para a citricultura do sul do Brasil

ABSTRACT: Diversification of rootstock varieties, with consequent reduction in phytosanitary risks, has great importance to the sustainability of citrus cultivation in the south of Brazil. This study evaluated the performance of 42 rootstocks in the nursery phase to generate 'Valencia Late' sweet orange seedlings. Therefore, nucellar seedlings from the rootstocks under study were analyzed in relation to plant height, stem diameter, mortality rate and percentage of bud set after grafting. The experimental design was completely randomized with four replications of 20 sample units. Not adapted genotypes had high mortality rates, and the ones of both hybrids LCR x CTSW - 009 and LVK x LCR - 038 were 100% and 90%, respectively. Other 13 genotypes had mortality rates above 30%, and 'Sunki' mandarin was the female genitor of ten of them. 'Swingle' citrumelo was the rootstock with the highest development (plant height and stem diameter), associated with low mortality rate. In relation to the other rootstocks, the best results were the fast grafting diameter, associated with low mortality rate obtained by hybrids HTR - 053, LRF x (LCR x TR) - 005, CLEO x TRBN - 245, CLEO x TRSW - 287, and citrandarins 'Indio', 'Riverside' and 'San Diego', as well as Trifoliate orange and 'Rangpur' lime. In addition to Trifoliate orange, which is widely used in Rio Grande do Sul, these rootstocks have great potential in citriculture in the south of Brazil.

RESUMO: A diversificação do uso de variedades porta-enxerto, com a consequente redução de riscos fitossanitários, é de fundamental importância para a sustentabilidade da citricultura do Sul do Brasil. O objetivo deste trabalho foi avaliar o comportamento de 42 porta-enxertos na formação de mudas de laranjeira 'Valência Late' em fase de viveiro. Nesse sentido, seedlings (plantas oriundas da germinação de sementes) nucelares dos porta-enxertos estudados foram avaliados relativamente aos caracteres altura da planta, diâmetro do caule, taxa de mortalidade e percentagem de pegamento de borbulhas após a enxertia. O delineamento experimental foi inteiramente casualizado, com quatro repetições de 20 unidades amostrais. Genótipos não adaptados tiveram altas taxas de mortalidade, os híbridos LCR x CTSW - 009 e LVK x LCR - 038 apresentaram 100% e 90% de mortalidade, respectivamente. Mais 13 genótipos apresentaram mortalidade superior a 30%, destes, dez têm como parental feminino a tangerineira 'Sunki'. O citrumelo 'Swingle' foi o porta-enxerto que apresentou maior desenvolvimento (altura da planta e diâmetro do caule), associado a uma baixa taxa de mortalidade. Quanto aos demais porta-enxertos, destacaram-se por atingir rapidamente o diâmetro de enxertia, associado a baixa taxa de mortalidade, os híbridos HTR - 053, LRF x (LCR x TR) - 005, CLEO x TRBN - 245, CLEO x TRSW - 287, citrandarins 'Indio', 'Riverside' e 'San Diego', assim como o limoeiro 'Cravo' e o Trifoliata. Além do Trifoliata, amplamente utilizado no Rio Grande do Sul, estes porta-enxertos são promissores para a citricultura do Sul do Brasil.

Epigenetic responses to Phytophthora citrophthora gummosis in citrus.

Studies show that DNA methylation is associated with plant immunity but little is known as to how this epigenetic mechanism assists plants in adjusting their responses to biotic stress, especially when interacting with an hemibiotrophic pathogen such as citrus Phytophthora. The aim of the present study was to assess the effects of scion-rootstock interaction on plant resistance to P. citrophthora infection and DNA methylation patterns in 'Pera' sweet orange and 'Tahiti' acid lime grafted onto 'Rangpur' lime and 'Tropical' sunki rootstocks reinoculated with P. citrophthora. Results showed that reinoculated plants of the 'Pera' sweet orange/'Rangpur' lime and 'Tahiti' acid lime/'Tropical' sunki combinations with more and less sensitive varieties to Phytophthora, presented smaller stem lesions and increased frequency of full methylation and hemimethylation rates, compared to inoculated plants. In contrast, 'Tahiti' acid lime/'Rangpur' lime, two highly sensitive varieties, and 'Pera'/'Tropical' sunki, two much less sensitive varieties, showed high increases in the frequency of hemimethylation and non-methylation levels. Results suggest that in citrus, both the scion-rootstock interaction and DNA methylation affect the response to P. citrophthora infection. Reinoculated plants, depending on the combination, showed changes in intracellular hyphae growth through the formation of sets of fibers and crystal accumulation in the periderm, cortex, and phloem. In addition, starch grain concentration was higher in reinoculated plants in comparison to inoculated plants. These findings support the assumption that DNA methylation is a plant defense mechanism and therefore may be exploited to improve the response of plants to the gummosis of P. citrophthora in citrus.

Integration of mandarin (Citrus reticulata) cytogenetic map with its genome sequence.

Citrus is an extremely important genus in terms of world fruit production. Despite its economic importance and the small genome sizes of its species (2n = 18, 1C = 430 ± 68 Mbp), entire genomic assemblies have only recently become available for some of its representatives. Together with the previous CMA/DAPI banding and fluorescence in situ hybridization (FISH) in the group, these data are important for understanding the complex relationships between its species and for assisting breeding programs. To anchor genomic data with the cytogenetic map of mandarin (Citrus reticulata), the parental species of several economically important hybrids such as sweet orange and clementine, 18 BAC (bacterial artificial chromosome) clones were used. Eleven clementine BACs were positioned by BAC-FISH, doubling the number of chromosome markers so far available for BAC-FISH in citrus. Additionally, six previously mapped BACs were end-sequenced, allowing, together with one BAC previously sequenced, their assignment to scaffolds and the subsequent integration of chromosomes and the genome assembly. This study therefore established correlations between mandarin scaffolds and chromosomes, allowing further structural genomic and comparative study with the sweet orange genome, as well as insights into the chromosomal evolution of the group.

Performance of the pineapple sweet orange on different rootstocks / Desempenho da laranja doce abacaxi em diferentes porta-enxertos

This study aimed at evaluating the agronomical performance of 'Pineapple' sweet orange grafted on ten rootstocks, in 2011-2017 harvests, so as to recommend the best combinations to be commercially explored in citrus growing regions in Bahia and Sergipe states, Brazil. An experiment wasinstalled to test ten rootstock for 'pineapple' sweet orange: 'Santa Cruz' Rangpur lime, 'Red Rough' Lemon, 'Orlando' Tangelo, 'Sunki Tropical' Mandarin, 'Swingle' citrumelo, the citrandarins 'Indio' and 'Riverside' and the hybrids HTR-051, LVKxLCR-010 and TSKxCTTR-002. The trial was installed in 2008 in the municipalityof Umbauba in Sergipe. The experimental design was complete randomized blocks with four replications and two plants per plot. Plant spacing was 6 x 4 m which corresponds to 416 plants per hectare and the orchard was rainfed and followed conventional management. The following agronomical parameters were evaluated: vegetative growth, drought tolerance, yield and physico-chemical quality of fruits as well as the abundance of phytophagous mites. Both hybrids LVK x LCR ­ 010 and TSKC x CTTR-002 and the 'Santa Cruz' rangpur lime bestowed higher tolerance to the dry period on the 'Pineapple' orange tree, by comparison with higher water deficit susceptibility conferred by the 'Orlando' tangelo and the 'Swingle' citrumelo. Rootstocks HTR-051, 'Riverside' citrandarin, 'Swingle' citrumelo and TSKC x CTTR-02 induced plants to remain small and, thus, showed aptitude for culture densification. Cumulative yield of the 'Pineapple' orange was higher on rootstocks 'Red Rough' lemon and 'Santa Cruz' Rangpur lime, the hybrid LVK x LCR-010 and 'Sunki Tropical'. Yield efficiency was not influenced by the rootstocks. Physico-chemical quality of fruits of 'Pineapple' orange is affected by the rootstocks and meets the requirements of juice industries. Regarding plant resistance, the rootstocks did not influence the population density of mites P. oleivora, E. banksi and T. mexicanus on 'Pineapple' oranges. Results show that both rootstocks 'Red Rough' lemon and 'Santa Cruz' rangpur lime conferred high regularity to 'Pineapple' orange trees in citrus growing regions in Bahia and Sergipe states

O objetivo deste trabalho foi avaliar o desempenho agronômico da laranjeira 'Pineapple' em combinação com dez porta-enxertos, nas safras 2011-2017, com vistas à recomendação das melhores combinações para exploração comercial na região citrícola dos estados da Bahia e de Sergipe. O experimento consistiu de laranja doce 'pineapple' enxertado nos porta-enxertos limoeiros 'Cravo Santa Cruz', limoeiro 'Rugoso Vermelho', tangeleiro Orlando, tangerineira 'Sunki' Tropical, citrumelo 'Swingle', citrandarins 'Indio', 'Riverside', além dos híbridos HTR ­ 051 e LVK x LCR ­ 010 e 'TSKC x CTTR ­ 002'. O trabalho foi instalado em 2008, no município de Umbaúba, em Sergipe, no delineamento experimental de blocos ao acaso, com quatro repetições, duas plantas por parcela, no espaçamento de 6m x 4m, correspondendo a uma população de 416 plantas· ha-1, com manejo em sistema de produção convencional, sem o uso de irrigação. Os seguintes parâmetros agronômicos foram avaliados: crescimento vegetativo, tolerância à seca, produção e qualidade físico-química de frutos, além da abundância de ácaros fitófagos. Os híbridos LVK x LCR - 010 e TSKC x CTTR - 002, assim como o limoeiro 'Cravo Santa Cruz', conferiram um maior nível de tolerância ao período seco, em contraste com maior suscetibilidade à seca relacionada ao tangelo 'Orlando' e ao citrumelo 'Swingle'. Os porta-enxertos HTR - 051, citrandarin 'Riversidade', citrumelo 'Swingle' e TSKC x CTTR - 002 induziram menor porte às plantas, demonstrando aptidão ao adensamento de plantio. A produção acumulada da laranjeira 'Pineapple' foi maior sobre os porta-enxertos limoeiros 'Rugoso Vermelho' e 'Cravo Santa Cruz', híbrido LVK x LCR - 010 e tangerineira 'Sunki Tropical'. A eficiência produtiva não foi influenciada pelos porta-enxertos. A qualidade física e química de frutos da laranjeira 'Pineapple' foi afetada pelos porta-enxertos e atendeu aos padrões exigidos pela indústria de sucos. Os porta-enxertos estudados não causaram variações nos níveis de populações dos ácaros Phyllocptruta oleivora, Eutetranychus banksi e Tetranychus mexicanus. Com base nos resultados conclui-se que os limoeiros 'Rugoso Vermelho' e 'Cravo Santa Cruz' determinam maior regularidade de produção de frutos à laranjeira 'Pineapple' nas regiões produtoras da Bahia e de Sergipe

Growth and fluorescence of 'Tahiti' acid lime/rootstock on Sunki mandarin hybrids under salinity / Crescimento e fluorescência de limeira ácida 'Tahiti' enxertada em híbridos de tangerineira sunki sob sal inidade

The objective of this study was to evaluate the ecophysiological behavior of 'Tahiti' acid lime/rootstock grafted on Sunki mandarin hybrids during the prefloration stage of the plants, in the field, under saline stress. The progenies originating from crossings of the 'Sunki' mandarin with 'Rangpur' lime and Poncirus trioliata, as rootstocks, combined with the 'Tahiti' acid lime as a scion. The experiment was carried out under field conditions, at the Federal University of Campina Grande (UFCG), Pombal PB fields. In drainage lysimeter of 150 dm3, studying 10 scion/rootstock combinations, irrigated with two water salinity levels (CEa) (S1 = 0.3 and S2 = 3.0 dS m-1) making a 10 x 2 factorial scheme. The experimental design was a randomized block design, with 3 replicates and each plot consisting of a useful plant, totalizing 60 parcels. The scion/rootstock plants were transplanted at one year of age from the rootstocks sowing, being the beginning of the applications of the saline stress to the 15 days after the transplant lasting until the period of flowering, that is, up to 195 days after transplanting, During this period the plants were analyzed for growth and chlorophyll fluorescence a. The combinations less sensitive to salinity were composed of the 'Tahiti' grafted with TSKFL x (LCR x TR) - 018, TSKFL x TRBK - 011 and TSKFL x TRBK - 030, it being possible to use saline water with up to 3.0 dS m-1 in irrigation. Salinity did not damage the biochemical phase of the scion/rootstock combinations, only affecting the initial fluorescence of the lighted tissue.

Objetivou-se estudar o crescimento e a fluorescência da clorofila a em limeira ácida 'Tahiti' enxertada em híbridos de tangerineira 'Sunki' sob salinidade da água durante a fase de préfloração das plantas. Assim, com base em um delineamento experimental de blocos ao acaso, foram avaliadas dez combinações copa/porta-enxerto, referentes à referida limeira ácida em combinação com dez porta-enxertos (nove híbridos e o limoeiro 'Cravo Santa Cruz' como testemunha), irrigadas com dois níveis de salinidade da água (CEa) (S1=0,3 e S2=3,0 dS m-1), perfazendo um esquema fatorial 10 x 2, que foi repetido em três blocos e com parcela constituída por uma planta útil, totalizando 60 parcelas. As mudas enxertadas foram transplantadas aos 365 dias após a semeadura dos porta-enxertos, em lisímetros de 150 dm3, que foram preenchidos com um Neossolo Flúvico da região, sendo o início das aplicações do estresse salino aos 15 dias após o transplante (DAT), perdurando até o período de floração, ou seja, até os 195 DAT, avaliando o crescimento e a fluorescência da clorofila a. As combinações com maior crescimento quando irrigadas com água de condutividade de 0,3dS-1 foram aquelas com os porta-enxertos TSKC x (LCR x TR) ­ 017, TSKC x (LCR x TR) ­ 012, TSKFL x (LCR x TR) ­ 018, TSKFL x TRBK ­ 011 e TSKFL x TRBK ­ 028. A salinidade não ocasionou dano à fase bioquímica das combinações copa/porta-enxerto, apenas afetado a fluorescência inicial do tecido iluminado. É possível usar água salina de até 3,0 -1 no cultivo de citros, caso se empreguem combinações menos sensíveis, como aquelas tendo como porta-enxertos os híbridos TSKC x (LCR x TR) ­ 017, TSKFL x (LCR x TR) ­ 018, TSKFL x TRBK ­ 011 e TSKFL x TRBK ­ 030.

Rootstock-induced molecular responses associated with drought tolerance in sweet orange as revealed by RNA-Seq.

BACKGROUND: Citrus plants are commercially propagated by grafting, with the rootstock variety influencing a number of horticultural traits, including drought tolerance. Among the different rootstock varieties available for citrus propagation, 'Rangpur' lime is known to confer enhanced tolerance to drought as compared to other citrus rootstocks. The objective of this study was to investigate the poorly understood molecular responses underlying the rootstock-induced drought tolerance in sweet orange. RESULTS: RNA-Seq transcriptome analysis was carried out in leaves of sweet orange grafted on 'Rangpur' lime subjected to control and drought-stress treatments, under greenhouse conditions, using the Illumina HiSeq platform. A total of 41,827 unique transcripts were identified, among which 1764 transcripts showed significant variation (P ≤ 0.001) between the treatments, with 1081 genes induced and 683 repressed by drought-stress treatment. The transcripts were distributed in 44 different categories of cellular component, molecular function and biological process. Several genes related to cell metabolism, including those involved in the metabolisms of cell wall, carbohydrates and antioxidants, light reactions, biotic and abiotic stress responses, as well as genes coding for transcription factors (TFs), protein kinases (PKs) and proteins involved in the abscisic acid (ABA) and ethylene signaling pathways, were differentially regulated by drought stress. RNA-Seq data were validated by quantitative real-time PCR (qPCR) analysis and comparative analysis of expression of the selected genes between sweet orange grafted on drought-tolerant and -sensitive rootstocks revealed new candidate genes for drought tolerance in citrus. CONCLUSIONS: In conclusion, our results showed that only a relatively small but functionally diverse fraction of the sweet orange transcriptome, with functions in metabolism, cellular responses and regulation, was differentially regulated by drought stress. The data suggest that the rootstock-induced drought tolerance in sweet orange includes the transcriptional activation of genes related to the cell wall, soluble carbohydrate and antioxidant metabolisms, biotic and abiotic stress responses, TFs, PKs and ABA signaling pathway, and the downregulation of genes involved in the starch metabolism, light reactions and ethylene signaling. Future efforts to elucidate their functional roles and explore their potential in the citrus genetic improvement should benefit from this data.

Recurrent water deficit causes alterations in the profile of redox proteins in citrus plants.

Plant acclimation to recurrent stress involves profound alterations in multiple genetic, metabolic and physiological processes. Stressful conditions usually implicate imbalance in reactive oxygen species (ROS) production and removal rates, which may lead to oxidative stress. However, the primary cellular targets of oxidative stress and their relevance in plant acclimation to abiotic stresses remains poorly characterized. By comparing redox proteomic and sugar profiles in citrus Valencia (VO) scions grafted onto two rootstocks with different soil water extraction capacities - Rangpur Lime (RL) and Sunki Maravilha (SM) - here we demonstrate that both ROS-mediated post-translational protein modification and changes in sugar composition are associated with acclimation to recurrent drought in citrus. The redox proteomic analysis of the distinct scion/rootstock combinations exposed to one (WD1), two (WD2) or three (WD3) water deficit episodes revealed a total of 32 and 55 redox protein spots present in VO/RL and VO/SM plants, respectively. Mass spectrometry analysis of these protein spots revealed essential targets of ROS-mediated posttranslational protein modification in citrus plants challenged by recurrent drought. The oxidation of cysteine thiol groups into glyceraldehyde 3-phosphate dehydrogenase (GAPDH) was shown to increase in WD3 samples of the VO/RL combination, whereas the opposite was observed for the VO/SM combination. Similarly, recurrent drought promoted the oxidation of catalase thiol groups in VO/SM, but not in VO/RL. Carbohydrate profiling revealed that glucose, fructose and galactose may also contribute to the phenotypic differences observed between the citrus genotypes exposed to drought. These findings reveal for the first time that recurrent drought differentially affects the profile of redox proteomics of citrus, suggesting that this alteration may be part of the stress memory in perennial plants.

Growth and physiology of citrus rootstocks under salt stress / Crescimento e fisiologia de porta-enxertos de citros sob estresse salino

In order to study the growth and physiology of citrus rootstocks under saline water irrigation, during formation of rootstocks, an assay was carried out in a factorial scheme, 2 x 6, corresponding to two levels of salinity of the nutrient solution: 0.3 and 4.0 dS m-1 and six genotypes provided by the Citrus Breeding Program of Embrapa Cassava & Fruits-CBP, distributed in randomized block design with three replications. The genotypes were: 1.'Santa Cruz Rangpur' lime (SCRL) (Citrus limonia Osbeck), 2. 'Florida Rough' lemon (FRL) (Citrus jambhiri Lush.), 3. 'Volkamer' lemon (VKL) (C. volkameriana V. Ten. &Pasq.), 4. CSM x SWC- 028, 5. CSM x SWC- 033 and 6.CSM x SWC-041, the last three hybrids of common 'Sunki' mandarin (CSM) [C.sunki (Hayata) hort. ex Tanaka] with 'Swingle' citrumelo (SWC) [C. paradisi Macfad. x Poncirus trifoliata (L.) Raf.]. Nucellar plants from these genotypes were grown in alternative hydroponic system, using Leonard jars. Application of nutrient solution made with saline water started from 90 days after sowing until 120 days, when the growth and physiology parameters of plants were evaluated. Salt stress influenced the growth and physiological parameters in all genotypes. Salt stress did not influence the chlorophyll a fluorescence in the genotypes VKL and CSM x SWC- 041, indicating no damage to the photosynthetic apparatus. The CSM x SWC- 041, 'Santa Cruz Rangpur' lime, 'Florida Rough' lemon and 'Volkamer' lemon are the more tolerant genotypes to salinity based on growth rate.

A fim de estudar o crescimento e a fisiologia de porta-enxertos de citros sob irrigação com água salina, durante a formação de porta-enxertos, realizou-se um ensaio fatorial 2 x 6, correspondente a dois níveis de salinidade da solução nutritiva: 0,3 e 4,0 dS m-1 e seis genótipos fornecidos pelo Programa de Melhoramento de Citros da Embrapa Mandioca & Fruticultura-PMGC, distribuídos em delineamento em blocos casualizados com três repetições. Os genótipos foram: 1. 'limoeiro Cravo Santa Cruz' (LCRSTC) (Citrus limonia Osbeck), 2. 'limoeiro Rugoso da Flórida' (LRF) (Citrus jambhiri Lush.), 3. 'limoeiro Volkameriano' (LVK) (C. Volkameriana V. Ten. & Pasq.), 4. CSM x SWC- 028, 5. CSM x SWC- 033 e 6. CSM x SWC-041, os últimos três híbridos de tangerineira 'Sunki' comum (CSM) [C. sunki (Hayata) hort. Ex Tanaka] com citrumelo 'Swingle' (SWC) [C. Paradisi Macfad. x Poncirus trifoliata (L.) Raf.] Plantas de origem nucelar desses genótipos foram cultivadas em sistema hidropônico alternativo, utilizando vasos Leonard. A aplicação de solução nutritiva feita com água salina iniciou-se a partir de 90 dias após a semeadura até 120 dias, quando foram avaliados os parâmetros de crescimento e fisiologia das plantas. O estresse salino influenciou o crescimento e os parâmetros fisiológicos em todos os genótipos. O estresse salino não influenciou a fluorescência da clorofila a nos genótipos VKL e CSM x SWC-041, indicando não haver danos ao aparelho fotossintético. O CSM x SWC-041, 'limoeiro Cravo Santa Cruz', 'limoeiro Rugoso da Flórida' e 'limoeiro Volkameriano' são os genótipos mais tolerantes à salinidade com base na taxa de crescimento.

Saline stress onto growth and physiology of trifoliate citrus hybrids during rootstock formation / Estresse salino no crescimento e fisiologia de híbridos trifoliados de citros enquanto porta-enxertos

High salts concentrations in soil and water are common in semi-arid regions, which reduces the growth and development of crops, especially sensitive plants, such as citrus, being important to identify tolerant materials as well as to study the physiology of these plants. An experiment was conducted evaluate the growth and physiology of citrus trifoliate citrus hybris during their early stage of development (seedling stage) under salt stress conditions. These hydrids were obtained through the Citrus Breeding Program of Embrapa Cassava & Fruits consisting of 'Common sunki' mandarin x 'Argentina' citrange - 019, 'Common sunki' mandarin x ('Rangpur' lime x Poncirus trifoliata) - 040, Trifoliate hybrids - 069, 116 and 127, distributed in a randomized block design with three replications. Nucellar seedlings of the genotypes were grown in an hydroponic system using Leonard jars. The application of nutrient solution with saline water started 90 days after sowing, extending to 120 days, when the seedlings were evaluated for plant growth and physiology. The genotypes common 'Sunki' mandarin x 'Argentina' citrange - 019, Common 'Sunki' mandarin x ('Rangpur' lime x P. trifoliata) - 040 and Trifoliate hybrid - 069 showed the greater tolerance to salinity, while the Trifoliate hybrid - 116 and 127 were found to be the less tolerant.

Altas concentrações de sais no solo e na água são comuns em regiões semiáridas, o que reduz o crescimento e o desenvolvimento das culturas, notadamente as sensíveis, como os citros, sendo importante a identificação de materiais tolerantes assim como o estudo da fisiologia destes. Assim, realizou-se um experimento para avaliar o crescimento e a fisiologia de híbridos de Poncirus trifoliata durante a formação de porta-enxertos sob condições de estresse salino. O experimento foi realizado usando um esquema factorial, 2 x 5, correspondendo a dois níveis de salinidade na solução nutritiva (2,6 e 6,3 dS m-1) e cinco híbridos de citros. Tais híbridos foram obtidos a partir do programa de melhoramento genético de citros da Embrapa Mandioca e Fruticultura, PMG ­ Citrus, a saber: tangerineira 'Sunki Comum' x citrange 'Argentina' ­ 019; tangerineira 'Sunki Comum' x (limoeiro 'Cravo' x Poncirus trifoliata) ­ 040 e os híbrido trifoliados ­ 069, 116 e 127. Os tratamentos foram distribuídos em delineamento experimental de blocos ao acaso, com três repetições. As plantas de origem nucelar dos genótipos foram cultivadas em sistema hidropônico por meio de vasos de Leonard. A aplicação das soluções nutritivas com águas salinas começaram aos 90 dias após a semeadura, se extendendo até os 120 dias, quando as plantas foram avaliadas em relação ao crescimento e a fisiologia. Os genótipos tangerineira 'Sunki Comum' x citrange 'Argentina' - -19, tangerineira Sunki Comum x x (limoeiro 'Cravo' x Poncirus trifoliata) ­ 040 e o híbrido trifoliado ­ 069 tiveram maior tolerância à salinidade, enquanto os híbridos trifoliados 116 e 127 foram os menos tolerantes.

Recurrent water deficit causes epigenetic and hormonal changes in citrus plants.

The present study evaluated the physiological, molecular and hormonal parameters from scion/rootstock interaction of citrus plants during recurrent water deficit. Responses of the Valencia (VO) scion variety grafted on two rootstocks with different soil water extraction capacities, Rangpur Lime (RL) and Sunki Maravilha (SM), during three successive periods of water deficit: plants exposed to a single episode of water deficit (WD1) and plants exposed to two (WD2) and three (WD3) recurrent periods of WD were compared. The combinations VO/RL and VO/SM presented polymorphic alterations of epigenetic marks and hormonal (i.e. abscisic acid, auxins and salicylicacid) profiles, which were particularly prominent when VO/SM plantswere exposed toWD3 treatment. Upon successive drought events, the VO/SM combination presented acclimatization characteristics that enable higher tolerance to water deficit by increasing transpiration (E), stomatal conductance (g s ) and photosynthetic rate (A), which in turn may have facilitated the whole plant survival. Besides providing comprehensive data on the scion/rootstock interactions upon successive stress events, this study brings the first dataset suggesting that epigenetic alterations in citrus plants triggered by recurrent water deficit lead to improved drought tolerance in this crop species.

Differential accumulation of flavonoids and phytohormones resulting from the canopy/rootstock interaction of citrus plants subjected to dehydration/rehydration.

Water scarcity can elicit drastic changes in plant metabolic and hormonal regulation, which may be of fundamental importance to stress tolerance. The study of plant the metabolic alterations in response to water deficit, especially the effects of the rootstocks level, is important to elucidate the mechanisms associated to drought tolerance. To verify the influence of rootstock and grafting on the tolerance to drought in citrus plants, we analyzed the growth, phytohormone levels and flavonoid profiles in grafted and ungrafted citrus plants subjected to different soil water regimes on plant status (well-watered, moderate drought and severe drought and rehydrated) under field conditions. The experiments were conducted under field conditions in the Brazilian Agricultural Research Corporation (EMBRAPA), Cruz das Almas, BA, Brazil. Water deficit reduced the total leaf area per plant in all canopy/rootstock combinations. Self-grafting reduce root volume, area and length when compared to ungrafted plants. Drought-induced increases in salicylic acid and abscisic acid associated with concomitant reductions in indoleacetic acid were observed in most canopy/rootstock combinations. However, plants with 'Sunki Maravilha' rootstocks exhibited the most pronounced changes in hormonal levels upon drought stress. Associated to these hormonal changes, drought also significantly affected flavonoid content and profile in both leaves and roots of the distinct citrus combinations. Glycosylated (GFs) and polimethoxylated flavonoids were predominantly found in leaves, whereas prenylated coumarins were found in the roots. Leaf levels of GFs (vicenin, F11, rutin and rhoifolin) were particularly modulated by drought in plants with 'Rangpur Santa Cruz' lime rootstock, whereas root levels of prenylated coumarins were most regulated by drought in plants with the 'Sunki Maravilha' root system. Taken together, these data indicate that the impacts of water deficit restriction on growth, hormonal balance and flavonoid profiles significantly varies depending on the canopy/rootstock combinations.

Expression of the citrus CsTIP2;1 gene improves tobacco plant growth, antioxidant capacity and physiological adaptation under stress conditions.

MAIN CONCLUSION: Overexpression of the citrus CsTIP2;1 improves plant growth and tolerance to salt and drought stresses by enhancing cell expansion, H 2 O 2 detoxification and stomatal conductance. Tonoplast intrinsic proteins (TIPs) are a subfamily of aquaporins, belonging to the major intrinsic protein family. In a previous study, we have shown that a citrus TIP isoform, CsTIP2;1, is highly expressed in leaves and also transcriptionally regulated in leaves and roots by salt and drought stresses and infection by 'Candidatus Liberibacter asiaticus', the causal agent of the Huanglongbing disease, suggesting its involvement in the regulation of the flow of water and nutrients required during both normal growth and stress conditions. Here, we show that the overexpression of CsTIP2;1 in transgenic tobacco increases plant growth under optimal and water- and salt-stress conditions and also significantly improves the leaf water and oxidative status, photosynthetic capacity, transpiration rate and water use efficiency of plants subjected to a progressive soil drying. These results correlated with the enhanced mesophyll cell expansion, midrib aquiferous parenchyma abundance, H2O2 detoxification and stomatal conductance observed in the transgenic plants. Taken together, our results indicate that CsTIP2;1 plays an active role in regulating the water and oxidative status required for plant growth and adaptation to stressful environmental conditions and may be potentially useful for engineering stress tolerance in citrus and other crop plants.

Survival strategies of citrus rootstocks subjected to drought.

Two citrus rootstocks, Rangpur lime (RL) and Sunki Maravilha mandarin (SM), were analyzed either ungrafted or grafted with their reciprocal graft combinations or with shoot scions of two commercial citrus varieties: Valencia orange (VO) and Tahiti acid lime (TAL). All graft combinations were subjected to distinct watering regimes: well-watered, severe drought and rehydration. Growth and water relation parameters, gas exchange as well as sugar and hormone profiles were determined. Data indicated that RL adopted a dehydration avoidance strategy and maintained growth, whereas SM adopted a dehydration tolerance strategy focused on plant survival. Compared with RL, the leaves and roots of SM exhibited higher concentrations of abscisic acid and salicylic acid, which induced drought tolerance, and accumulation of carbohydrates such as trehalose and raffinose, which are important reactive oxygen species scavengers. SM rootstocks were able to transfer their survival strategy to the grafted shoot scions (RL, VO, TAL). Because of their contrasting survival strategies, RL reached the permanent wilting point more quickly than SM whereas SM recovered from prolonged droughts more efficiently than RL. This is one of the most complete studies of drought tolerance mechanisms in citrus crops and is the first to use reciprocal grafting to clarify scion/rootstock interactions.

Citrus rootstocks influence the population densities of pest mites / Porta-enxertos cítricos influenciam a densidade populacional de ácaros fitófagos

Citrus are attacked by pest mites such as the citrus rust mite Phyllocoptruta oleivora (Ashmead) (Acari: Eriophyidae) and the spider mite Tetranychus mexicanus (McGregor) (Acari: Tetranychidae). However, little is known on citrus rootstocks influencing pest mites. We aimed to evaluate the influence of rootstocks on population densities of pest mites on the sweet oranges 'Pera CNPMF D-6' and 'Valencia Tuxpan' throughout time. Adults of both mite species were monthly counted during 19 months from June 2011 to February 2013. Rootstocks influenced the populations of pest mites, since lower densities of P. oleivora were found on 'Pera CNPMF D-6' sweet orange grafted on the hybrid TSKC × CTTR - 002 and on 'Swingle' citrumelo in comparison with the hybrid LVK × LCR - 010, 'Red' rough lime and 'Santa Cruz' rangpur lime as rootstocks. Similarly, lower densities of T. mexicanus were found on 'Valencia Tuxpan' sweet orange grafted on the hybrid HTR-051 in comparison to 'Indio' citrandarin, 'Sunki Tropical' mandarin and LVK × LCR - 010 as rootstocks. We concluded that densities of the mites P. oleivora and T. mexicanus on the sweet oranges 'Pera CNPMF D-6' and 'Valencia Tuxpan' were affected in some periods of the year by some rootstocks, suggesting influence of some genotypes on these pests.

Os citros são atacados por ácaros-praga como o ácaro-da-falsa-ferrugem Phyllocoptruta oleivora (Ashmead) (Acari: Eriophyidae) e Tetranychus mexicanus (McGregor) (Acari: Tetranychidae). No entanto, pouco é conhecido sobre o efeito de porta-enxertos sobre populações de pragas. O objetivo deste trabalho foi avaliar a influência de porta-enxertos nas densidades populacionais de ácaros-praga nas laranjeiras 'Pera CNPMF D-6' e 'Valência Tuxpan' ao longo do tempo. Adultos das espécies de ácaro citadas foram quantificados mensalmente, durante 19 meses, de junho de 2011 a fevereiro de 2013. Os porta-enxertos influenciaram as populações dos ácaros-praga, uma vez que menores densidades de P. oleivora foram encontradas em laranjeira 'Pera CNPMF D-6', enxertada no híbrido TSKC × CTTR - 002 e no citrumelo 'Swingle', em comparação com o que se observou em relação aos porta-enxertos LVK × LCR - 010, limoeiro 'Rugoso vermelho' e limoeiro 'Cravo Santa Cruz'. Similarmente, menores densidades de T. mexicanus ocorreram em laranjeira 'Valência Tuxpan' enxertada no híbrido HTR-051, em comparação com o que se deu em relação aos porta-enxertos citrandarin 'Indio', tangerineira 'Sunki Tropical' e LVK × LCR - 010. Concluiu-se que as densidades dos ácaros P. oleivora e T. mexicanus nas laranjeiras 'Pera CNPMF D-6' e 'Valencia Tuxpan' foram afetadas pelo porta-enxerto em determinados períodos do ano, sugerindo influência de alguns genótipos sobre essas pragas.

Ectopic expression of a fruit phytoene synthase from Citrus paradisi Macf. promotes abiotic stress tolerance in transgenic tobacco.

Abscisic acid (ABA) is an important regulator of plant responses to environmental stresses and an absolute requirement for stress tolerance. Recently, a third phytoene synthase (PSY3) gene paralog was identified in monocots and demonstrated to play a specialized role in stress-induced ABA formation, thus suggesting that the first committed step in carotenogenesis is a key limiting step in ABA biosynthesis. To examine whether the ectopic expression of PSY, other than PSY3, would similarly affect ABA level and stress tolerance, we have produced transgenic tobacco containing a fruit-specific PSY (CpPSY) of grapefruit (Citrus paradisi Macf.). The transgenic plants contained a single- or double-locus insertion and expressed CpPSY at varying transcript levels. In comparison with the wild-type plants, the CpPSY expressing transgenic plants showed a significant increase on root length and shoot biomass under PEG-, NaCl- and mannitol-induced osmotic stress. The enhanced stress tolerance of transgenic plants was correlated with the increased endogenous ABA level and expression of stress-responsive genes, which in turn was correlated with the CpPSY copy number and expression level in different transgenic lines. Collectively, these results provide further evidence that PSY is a key enzyme regulating ABA biosynthesis and that the altered expression of other PSYs in transgenic plants may provide a similar function to that of the monocot's PSY3 in ABA biosynthesis and stress tolerance. The results also pave the way for further use of CpPSY, as well as other PSYs, as potential candidate genes for engineering tolerance to drought and salt stress in crop plants.

Karyotype diversity and the origin of grapefruit.

Grapefruit is a group of citrus of recent origin, probably resulting from a cross between pummelo and sweet-orange. Aiming to investigate this putative origin and the genetic variability among grapefruit cultivars, the karyotype of six grapefruits, two pummelos, and one tangelo cultivar (grapefruit x tangerine) were analyzed using sequential CMA/DAPI double staining and FISH with rDNA probes. The karyotypes of grapefruit 'Duncan' and 'Foster' differ from those of 'Flame', 'Henderson', 'Marsh' and 'Rio Red'. The former have two chromosomes with a single CMA(+) band in both terminal regions (C type chromosome) and six chromosomes with only one CMA(+) terminal band (D type), whereas the latter have three C and five D type chromosomes. All accessions investigated exhibited two chromosomes with 5S rDNA but a variable number of 45S rDNA. The two former grapefruits displayed four 45S rDNA sites, whereas the remaining grapefruit cultivars had five. The two pummelos showed identical karyotypes, homozygous for CMA(+) bands and their four rDNA sites. From each pummelo chromosome pair one chromosome seems to be present in grapefruit karyotypes. The different grapefruit karyotypes might result from independent crosses between pummelos of different karyotypic constitution and sweet-oranges. The chromosome markers found in the tangelo 'Orlando' and the position of their two 45S rDNA confirm the grapefruit 'Duncan' and the tangerine 'Dancy' as their parents.