The domestication of citrus, is poorly understood. Cultivated types are selections from, or hybrids of, wild progenitor species, whose identities and contributions remain controversial. By comparative analysis of a collection of citrus genomes, including a high quality haploid reference, we show that cultivated types were derived from two progenitor species. Though cultivated pummelos represent selections from a single progenitor species, C. maxima, cultivated mandarins are introgressions of C. maxima into the ancestral mandarin species, C. reticulata. The most widely cultivated citrus, sweet orange, is the offspring of previously admixed individuals, but sour orange is an F1 hybrid of pure C. maxima and C. reticulata parents, implying that wild mandarins were part of the early breeding germplasm. A wild “mandarin” from China exhibited substantial divergence from C. reticulata, suggesting the possibility of other unrecognized wild citrus species. Understanding citrus phylogeny through genome analysis clarifies taxonomic relationships and enables sequence-directed genetic improvement.

Genomics of the origin and evolution of CitrusGuohong albert Wu 1 , Javier Terol 2 , Victoria ibanez 2 , antonio López-García 2 , estela Pérez-román 2 , carles borredá 2 , concha Domingo 2 , francisco r. Tadeo 2 , Jose carbonell-caballero 3 , roberto alonso 3 , franck curk 4 , Dongliang Du 5 , Patrick Ollitrault 6 , Mikeal L. roose 7 , Joaquin Dopazo 3,8 , frederick G. Gmitter Jr 5 , Daniel S. rokhsar 1,9,10 & Manuel Talon 2The genus Citrus and related genera (Fortunella, Poncirus, Eremocitrus and Microcitrus) belong to the angiosperm subfamily Aurantioideae of the Rutaceae family, which is widely distributed across the monsoon region from west Pakistan to north-central China and south through the East Indian Archipelago to New Guinea and the Bismarck Archipelago, northeastern Australia, New Caledonia, Melanesia and the western Polynesian islands 1 . Native habitats of citrus and related genera roughly extend throughout this broad area (Extended Data Fig. 1a and Supplementary Table 1), although the geogra phical origin, timing and dispersal of citrus species across southeast Asia remain unclear. A major obstacle to resolving these uncertainties is our poor understanding of the genealogy of complex admixture in cultivated citrus, as has recently been shown 2 . Some citrus are clonally propagated apomictically 3 through nucellar embryony, that is, the development of non-sexual embryos originating in the maternal nucellar tissue of the ovule, and this natural process may have been co-opted during domestication; grafting is a relatively recent phenomenon 4 . Both modes of clonal propagation have led to the domestication of fixed (desirable) genotypes, including interspecific hybrids, such as oranges, limes, lemons, grapefruits and other types.Under this scenario, it is not surprising that the current chaotic citrus taxonomy-based on long-standing, conflicting proposals 5,6 -requires a solid reformulation consistent with a full understanding of the hybrid and/or admixture nature of cultivated citrus species. Here we analyse genome sequences of diverse citrus to characterize the diversity and evolution of citrus at the species level and identify citrus admixtures and interspecific hybrids. We further examine the network of relatedness among mandarins and sweet orange, as well as the pattern of the introgression of pummelos among mandarins for clues to the early stages of citrus domestication. Diversity and evolution of the genus CitrusTo investigate the genetic diversity and evolutionary history of citrus, we analysed the genomes of 58 citrus accessions and two outgroup genera (Poncirus and Severinia) that were sequenced to high coverage, including recently published sequences 2,3,7 as well as 30 new genome sequences described here. For our purpose, we do not include accessions related by somatic mutations. These sequences represent a diverse sampling of citrus species, their admixtures and hybrids (Supplementary Tables 2, 3 and Supplementary Notes 1, 2). Our collection includes accessions from eight previously unsequ...

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Citrus is the main fruit tree crop in the world and therefore has a tremendous economical, social and cultural impact in our society. In recent years, our knowledge on plant reproductive biology has increased considerably mostly because of the work developed in model plants. However, the information generated in these species cannot always be applied to citrus, predominantly because citrus is a perennial tree crop that exhibits a very peculiar and unusual reproductive biology. Regulation of fruit growth and development in citrus is an intricate phenomenon depending upon many internal and external factors that may operate both sequentially and simultaneously. The elements and mechanisms whereby endogenous and environmental stimuli affect fruit growth are being interpreted and this knowledge may help to provide tools that allow optimizing production and fruit with enhanced nutritional value, the ultimate goal of the Citrus Industry. This article will review the progress that has taken place in the physiology of citrus fruiting during recent years and present the current status of major research topics in this area. Key words: abiotic stresses, abscission, color break, flowering, fruit set, ripening Fisiologia da frutificação em citrus. Citrus é a principal fruteira no mundo, tendo, portanto, profundos impactos econômicos, sociais e culturais em nossa sociedade. Nos últimos anos, o conhecimento sobre a biologia reprodutiva de plantas tem aumentado consideravelmente, principalmente em função de trabalhos desenvolvidos com plantas-modelo. Todavia, a informação produzida nessas espécies nem sempre pode ser aplicada a citrus, fundamentalmente porque citrus é uma cultura arbórea perene com uma biologia reprodutiva muito peculiar e incomum. A regulação do crescimento e desenvolvimento do fruto em citrus é um fenômeno complexo e dependente de muitos fatores externos e internos que podem operar tanto seqüencialmente como simultaneamente. Os elementos e mecanismos pelos quais estímulos ambientes e endógenos afetam o crescimento do fruto vêm sendo interpretados, e esse conhecimento pode auxiliar a prover ferramentas que permitiriam otimizar a produção per se, além da obtenção de frutos com maior valor nutricional, o objetivo precípuo da Industria de Citrus. Neste artigo, revisam-se os avanços que vêm ocorrendo na fisiologia da frutificação de citrus durante os últimos anos; apresenta-se, também, o status atual de pesquisas mais relevantes nessa área. Palavras-chave: estresses abióticos, floração, maturação, vingamento de frutos

Isotope dilution analysis indicated that epi-GA 1 was an arte-The plant-growth-promoting rhizobacteria (PGPR), Bacillus pumilus and Bacillus licheniformis, isolated from the rhizo-fact. Likewise, iso-GA 3 is also probably an artifact spontaneously formed during extraction and/or analysis. In both sphere of alder (Alnus glutinosa [L.] Gaertn.) have a strong growth-promoting activity. Bioassay data showed that the culture media, GA 1 was present in higher concentrations (130-150 ng ml − 1 ) than GA 3 (50-60 ng ml − 1 ), GA 4 (8-12 dwarf phenotype induced in alder seedlings by paclobutrazol (an inhibitor of gibberellin [GA] biosynthesis) was effectively ng ml − 1 ) and GA 20 (2-3 ng ml − 1 ). The data indicated that culture of both bacteria accumulate bioactive C 19 -gibberellins reversed by applications of extracts from media incubated with both bacteria and also by exogenous GA 3 . Full-scan gas in relative high amounts and that these GAs appear to be physiologically active in the host plant. The evidence suggests chromatography-mass spectrometry analyses on extracts of these media showed the presence of GA 1 , GA 3 , GA 4 and that the promotion of stem elongation induced by the PGPR GA 20 , in addition to the isomers 3-epi-GA 1 and iso-GA 3 . could be mediated by bacterial GAs.