Sour orange (Citrus aurantium L.) is a very well-known citrus product. As sweet orange [Citrus sinensis (L.) Osbeck], it originated from the crossing between mandarin (Citrus reticulata Blanco) and pummelo [Citrus maxima (Burm.) Merril]. In order to investigate the origin and variability of its karyotype, eight cultivars of C. aurantium and one cultivar of Citrus natsudaidai Hayata, closely related to C. aurantium, were characterized with the fluorochromes CMA (chromomycin A₃) and DAPI (4′-6-diamidino-2-phenylindole) and FISH (fluorescent in situ hybridization) with 5S and 35S rDNA, as well as BAC (bacterial artificial chromosomes) probes. The sour orange accessions analyzed presented three distinct karyotype formulae, but six of eight accessions had the formula 1A + 1B + 1C + 8D + 7F. Citrus natsudaidai presented the formula 2A + 1C + 6D + 9F. The accessions ‘Smooth Flat Seville’, ‘Standard’, and ‘Thornless’ presented three sites of 35S rDNA in total, in A or B chromosomes, as well as in one D. The accessions ‘Smooth Flat Seville’ and ‘Thornless’ presented always two sites of 5S rDNA, in one F and one D chromosomes. The presence of chromosome types A/35S and F/5S reinforces C. aurantium as a first-generation hybrid derived from C. maxima, while a D/5S-35S chromosome corroborates C. reticulata as a second parent. However, several chromosome changes occurred after the hybridization event, which can be partly explained by the reduction of heterochromatic blocks and partly by the occurrence of introgressions in some accessions.

酸橙（Citrus aurantium L.）是一种非常著名的柑橘产品。作为甜橙[ Citrus sinensis（L.）Osbeck]，它起源于普通话（Citrus reticulata Blanco）和柚子[ Citrus maxima（Burm。）Merril]之间的杂交。为了调查其核型的起源和变异，八个品种酸橙和一个品种柑橘natsudaidai隼太密切相关的酸橙，表征与荧光CMA（色霉素一₃）和DAPI（4'-6-diamidino-2-phenylindole）和FISH（荧光原位杂交）与5S和35S rDNA，以及BAC（细菌人工染色体）探针。分析的酸橙种质呈现三个不同的核型式，但八个种质中的六个具有式1A + 1B + 1C + 8D + 7F。柑橘夏代（Citrus natsudaidai）给出了公式2A + 1C + 6D + 9F。保藏号“ Smooth Flat Seville”，“ Standard”和“ Thornless”在A或B染色体以及一个D染色体上总共呈现出35个rSDNA的三个位点。总是在一个F和一个D染色体上有5S rDNA的两个位点。染色体类型A / 35S和F / 5S的存在增强了尖酸梭菌，作为源自最大梭菌的第一代杂种，而D / 5S-35S染色体证实网状线虫是第二亲本。但是，杂交事件发生后发生了几条染色体变化，这可以部分解释为减少异色块，部分解释为某些种质渗入。