Alborea: A New Mid-late Mandarin Triploid Hybrid [(Citrus clementina x C. tangerina) x (C. nobilis x C. deliciosa)]

Citrus is one of the most important fruit crops worldwide, with more than 130 million tons produced in 2017. Mandarins represent 25% of this production (Food and Agriculture Organization, 2018) and are mainly destined for fresh consumption. The Mediterranean area is the most important region for mandarin exports, with 60% of the total volume, and Spain is the leading country. The fresh market demands high-quality, seedless fruit that can be harvested throughout the marketing season. Therefore, mandarin breeding programs worldwide are mainly aimed at obtaining new, seedless, easy-peeling varieties with an attractive fruit color and flavor, and with high organoleptic characteristics (Grosser et al., 2010; Navarro et al., 2015; Rapisarda et al., 2008). The mandarin varietal structure in Spain has several problems. It includes satsumas [Citrus unshiu (Mak.) Marc.], clementines (C. clementina Hort. ex Tan.), and mandarin hybrids. Satsumas are harvested from the end of August to mid November. Their pollen and ovules are not viable, and thus they are seedless. Clementine varieties are the most important group of mandarins in Spain and can be harvested from mid September until the second half of January. They are self-incompatible, but their pollen and ovules are viable and, consequently, they are able to pollinate and be pollinated with other compatible cultivars. ‘Hernandina’ clementine, our latest maturing clementine, is characterized by low fruit quality when grafted onto ‘Carrizo’ citrange [C. sinensis (L.) Osbeck × Poncirus trifoliata (L.) Raf.], which is by far the predominant rootstock in our country. Fruit peel deteriorates quickly after mid January, and in practice no clementine fruit is available in the second half of January. Mandarin hybrids, such as ‘Nova’ [C. clementina × (C. paradisi Macf. × C. tangerina Hort. Ex Tan.)], ‘Fortune’ (C. clementina × ?), ‘Murcott’ (C. reticulata Blanco × C. sinensis), and ‘Ortanique’ (natural hybrid between mandarin and C. sinensis), were introduced to our citriculture to cover the demand of late-maturing mandarins by international markets. These cultivars are self-incompatible, but their pollen and ovules are viable and they cross-pollinate with clementines, producing seedy fruit in both groups of mandarins. In addition, some late mandarin hybrids, such as ‘Fortune’, ‘Nova’, and ‘Murcott’, are susceptible to Alternaria alternata fungus, which reduces production and depreciates the fruit commercially for the fresh-fruit market. This fungus has forced the top-grafting of trees of these susceptible cultivars, particularly ‘Fortune’, and during the past few decades there has been a decrease in late-mandarin plantations and an increase in clementine plantings, mainly ‘Clemenules’. This has created an imbalance between production and market demand that has caused a drastic reduction in prices for the growers such that, in many cases, they cannot even sell their products. As a consequence of excessive clementine production, a lot of growers decided to cultivate other late mandarin cultivars, especially ‘Nadorcott’ [(C. reticulata × C. sinensis) × ?], ‘Tango’ (irradiated variety from ‘Nadorcott’ mandarin), and ‘Orri’ (irradiated variety from ‘Orah’ mandarin) and, more recently, ‘Spring Sunshine’ (irradiated variety from ‘Murcott’ mandarin), which is susceptible to Alternaria. These varieties cover the period from February to the end of April and are managed by different private companies that limit the number of plants or the cultivated area, and also impose high royalties that, in many cases, are difficult for growers to pay. Under this scenario, the recovery of a new, high-quality seedless mandarin cultivar that matures from mid December until the end of January, when there are no other high-quality mandarins in the market, and that is resistant to Alternaria is a very important objective for our citriculture. In 1995, a triploid breeding program was started at the Instituto Valenciano de Investigaciones Agrarias (IVIA) with the objective of producing new mid- and late-maturing triploid cultivars resistant to A. alternata fungus through sexual hybridization, embryo rescue, and ploidy analysis by flow cytometry (Navarro et al., 2015). Triploid plants generally produce aneuploid gametes, thus leading to very low fertility of their pollen and ovules (Otto and Whitton, 2000). For this reason, citrus triploid hybrids can be considered sterile, producing seedless fruit, and do not induce seed formation in other varieties by cross-pollination, even in the presence of bees (Navarro et al., 2015). A routine strategy exploited for triploid citrus breeding is spontaneous female unreduced gamete formation in diploid × diploid crosses (Aleza et al., 2012; Cuenca et al., 2011, 2015), where triploid hybrids arise usually from the union of an unreduced megagametophyte formed through a second-division restitution mechanism with a haploid pollen (Cameron and Frost 1968; Cuenca et al., 2011; 2015; Esen and Soost 1971, 1973; Geraci et al., 1975; Luro et al., 2004). Triploid embryos are predominantly found in small seeds, which generally do not germinate in greenhouse conditions. Thus, embryo rescue from these small seeds is required to reach high germination rates (Aleza et al., 2010b). In addition, ploidy level determination by flow cytometry is also required in extensive triploid citrus breeding programs (Aleza et al., 2012). From this program, the mid- to late-maturing triploid varieties ‘Garbı’ [(C. clementina × C. tangerine) × (C. reticulata × C. sinensis)] (Aleza et al., 2010a) and ‘Safor’ [(C. clementina × C. tangerina) × (C. unshiu × C. nobilis Lour.)] (Cuenca et al., 2010) were released, with more than 600,000 plants commercialized until 2018. We describe a new triploid hybrid named ‘Alborea’ mandarin [(C. clementina × C. tangerina) × (C. nobilis × C. deliciosa Ten.)] that is resistant to Alternaria alternata and characterized by the production of high-quality, seedless fruit that can be harvested from mid-December until the end of January

Identificación of ovule and seed genes from Citrus clementina

Seedlessness is a highly desirable trait in fresh fruit. Citrus varieties, such as Clementine mandarin and other related species, show parthenocarpic fruit development without seeds due to self-incompatibility. In spite of that, these fruits frequently contain seeds as a result of cross-pollination by insects with compatible pollen from other citrus cultivars grown nearby. To solve this problem using a biotechnological approach we aim at the destruction of ovules and/or seeds by directing the expression of a toxic gene using the promoter of an ovule and/or seed specific gene. With the purpose of isolating this kind of genes we constructed two cDNA libraries from ovules and seeds at different developmental stages of the Clementine mandarin (Citrus clementina cv. Clemenules). A total of 1,014 ESTs from the ovule library and 1,042 ESTs from the seed library were generated, with a novelty percentage of 27% and 36% among the Spanish Citrus Functional Genomic Project (CFGP) ESTs database, respectively. Quantitative PCR analysis confirmed nearly specific expression in ovule and/or seed of two genes, TRANSPARENT TESTA16 (CcTT16) and TRANSPARENT TESTA7 (CcTT7). Expression of these two genes is restricted to early seed development, and is localized in the embryo sac and endothelium. The promoters of those genes may be useful to genetically engineer citrus species to avoid seed formation in fruits of commercial varieties.This work was supported by grants from the Conselleria de Agricultura, Pesca y Alimentacion (Generalitat Valenciana) and Spanish Ministerio de Ciencia y Tecnologia (research grant GEN2001-4885-C05). A.G-L. received a PhD fellowship from the Conselleria de Agricultura, Pesca y Alimentacion.Peer reviewe

Very large photoconduction enhancement upon self-assembly of a new triindole derivative in solution-processed films

A new carbazole-related small molecule exhibiting self-assembly into ordered nanostructures in solution-processed cast films has been synthesized and its charge-photogeneration and -transport properties have been investigated. Large photoconductivity was measured in the amorphous state while an enormous improvement in the photoconduction properties was observed when the molecules spontaneously organized. Photocurrents increased upon self-assembly by up to four orders of magnitude, mostly due to the drastic enhancement of the charge photogeneration. A greatly favorable arrangement of the aromatic cores in the resulting nanostructures, which were characterized by X-ray analysis, may explain these improvements. Photocurrents of mA cm-2, on/off ratios of 104 and quantum efficiencies of unity at low field and light intensity, which are among the best values reported to date, along with the simplicity of fabrication, give this readily-available organic system great potential for use in plastic optoelectronic devices. Large photoconduction enhancement from small molecules: A new carbazole-related small molecule exhibiting self-assembly into ordered nanostructures in solution-processed cast films has been synthesized and its charge-photogeneration and -transport properties have been investigated. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.This work was supported by MAT2005-07369-C03, CTQ2007-65683/BQU, MAT2008-06648-C02-01 and S2009/MAT-1756/CAM). F.G.G. thanks the program Juan de la Cierva of the Spanish Government MEC (grant JCI-2006-3029-2615). E.M.G.F. thanks the Consejo Superior de Investigaciones Cientificas (Program I3P) for a postdoctoral contract.Peer Reviewe

Symmetry lowering in triindoles: Impact on the electronic and photophysical properties

The electronic and photophysical properties of 6,11-dihydro-5H-diindolo[2, 3-a:2′,3′-c]carbazole, an asymmetric cyclic dehydrotrimer of indole, have been explored and compared to its symmetric analogue, 10,15-dihydro-5H- diindolo[3,2-a:3′,2′-c]carbazole (triindole), a well-known high hole mobility semiconductor. To this purpose, we use a joint experimental and theoretical approach that combines absorption and emission spectroscopies, cyclic voltammetry, and spectroelectrochemistry with DFT calculations. Lowering the symmetry of the triindole platform causes a red-shift of the absorption edge and emission maxima and improved the fluorescence quantum yield. Cyclic voltammetry and spectroelectrochemistry reveal the reversible nature of the two observable oxidation processes in the alkylated asymmetric triindoles together with an increase in the stabillity of their oxidized species. On the other hand, the insertion of alkyl groups on the nitrogen atoms results in a further fluorescence enhancement although larger reorganization energies are found. DFT and time-dependent (TD-DFT) calculations successfully support the experimental data and aid in the understanding of the tuning of the physicochemical properties of the triindole platform upon symmetry lowering toward their incorporation in electronic devices. © 2014 American Chemical Society.This work was financially supported by the MICINN of Spain (CTQ2010-18813) and the CAM (Project S2009/MAT-1756/CAM), MINECO of Spain (CTQ2012-33733), Junta de Andalucía (P09-FQM-4708). M.C.R.D. thanks the MICINN for a “Ramón y Cajal” Research contract. D.A.S.F. gratefully acknowledges the financial support from the Brazilian Research Councils CNPq CAPES, CNPq (grant 303084/2010-3) and FAP-DF (Fundaçâo de Apoio à Pesquisa do Distrito Federal).Peer Reviewe