Tetraploidy in Citrus.
Tetraploidy in Citrus.
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柑橘的四倍体。
DOI：
10.1073/pnas.11.9.535
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发表时间：
1925
影响因子：
11.1
通讯作者：
H. Frost
中科院分区：
文献类型：
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作者：
H. Frost
由河滨霍华德·B·弗罗斯特柑橘试验站提供的加州柑橘种子通常含有不定胚，通常是在卵子受精后，通过邻近胚囊的珠心细胞增殖而产生的。因此，从这些胚胎发育出来的幼苗在它们的遗传上完全是“母体”的，在种间杂交中，它们通常可以很容易地从受精产生的杂种中区分出来，甚至在结果之前就可以区分开来。在Citrus试验站育种园中生长的异花授粉的柑橘后代中，“无配子”个体的比例通常约占种子亲本品种幼苗总数的20%至85%。除了普通的无配子后代外，还经常发现另一种形式，这种形式没有表现出花粉亲本的特征，因此显然是无性产生的。这种变异形式与普通的无配子生殖后代截然不同，其差异特征在所涉及的不同物种和植物变种中是如此相似，以至于强烈地提出了这种变异形式的单一起源模式。它的生长速度比相同亲本的正常无配子后代稍慢一些，大约在一到两年后才开花。它长着粗壮的枝条和荆棘，叶子又宽又厚。它已被指定为“厚叶植物”。最近发现，三个柑橘园艺品种的单倍体染色体数，或它们无配子生殖的明显相同的种子后代的单倍体染色体数为9。3图1，4说明了这一点，它显示了来自种间杂交的纸皮(St.Michael)橙(Citrussinensis Osbeck)正常无配子后代的花粉母细胞的第二个中期。每组明显有9条染色体。粗叶树目前还没有开出几朵花，但已经从刚才提到的二倍体树的一个粗叶兄弟姐妹的几个芽的花粉母细胞中获得了染色体计数。在第二次中期和后期，每组染色体数约为18条(图3)。2)。这个数字似乎变化很大，已经得到了16，17，18，19和20个数字。很明显，与四倍体曼陀罗一样，在第一中期出现5个不分离的现象非常频繁。第一个中期的偏光图表明，染色体像往常一样配对，而且部分或全部二价体通常或多或少以四价基团紧密相关。在迄今观察到的少数情况下，四价体的形成是。比四倍体曼陀罗普遍得多，显然是次要的或次要的。
By HOWARD B. FROST CITRUS EXPERIMENT STATION, RIVERSIDE, CALIFORNIA Citrus seeds often contain adventitious embryos, produced, usually subsequent to fertilization of the egg, by proliferation of nucellar cells adjoining the embryo sac. 2 Seedlings developed from these embryos are therefore entirely" maternal" in their inheritance, and in interspecific crosses they can usually be readily distinguished, even in advance of fruit-ing, from the hybrids that result from fecundation. Among the Citrus progeny from cross-pollination that are now growing in the breeding orchard at the CitrusExperiment Station, the proportion of" apogamic" individuals usually ranges about from 20 to 85 per cent of the whole number of seedlings of a seed-parent variety. Besides the ordinary apogamic progeny, another form that shows no characters of the pollen parent, and therefore is obviously produced asexually, has frequently been found. This form'is strikingly distinct from the ordinary apogamic progeny, and its differential characters are so similar in the various species and botanical varieties concerned that a single mode of origin of this aberrant form is strongly suggested. It is somewhat slower in growth than the normal apogamic progeny of the same parentage, and is about one or two years later in its first flowering. It has stout shoots and thorns, and broad, thick leaves. It has been designated" thick-leaved." The haploid number of chromosomes in three horticultural varieties of Citrus, or in their apparently identical seed progeny produced apogam--ically, has recently been found to be9. 3 This is illustrated by figure 1, 4 which shows the second metaphase in a pollen mother cell of normal apogamic progeny of Paper Rind (St. Michael) orange (Citrus sinensis Osbeck) from an interspecific cross. There are clearly 9 chromosomes in each group.Few flowers have as yet been produced by the thick-leaved trees, but chromosome counts have been obtained from pollen mother cells of several'buds of a thick-leaved sib of the diploid tree just mentioned. At the second metaphase and anaphase the number of chromosomes in each group approximates 18 (fig. 2). The number seems highly variable, and counts of 16, 17, 18, 19 and 20 have been obtained. Evident-ly, as in tetraploid Datura, 5 non-disjunction occurs very frequently at the first-metaphase. Polarviews at the first metaphase indicate that the chromo-somes are paired as usual, and that part or all of the bivalents are often more or less closely associated in quadrivalent groups. In the small number of cases so far observed, the formation of quadrivalents is. much-less general than in tetraploid Datura, and is obviously secondary to or-