Common dallisgrass (Paspalum dilatatum) is an apomictic pentaploid (2n=5x=50) of hybrid origin with irregular meiosis and with the genome formula IIJJX. The I and J genomes are homologous to those of diploid P. intermedium and P. jurgensii, respectively, but the source of the X genome is unknown. Members of the X genome may have genes of special biological significance, including those controlling apomixis. Common dallisgrass was crossed with several diploid Paspalum species in an attempt to identify the source of the X genome. Since common dallisgrass is apomictic, all hybrids produced will be formed by fertilization of an unreduced egg (2n+n). Any hybrid showing 30 chromosome bivalents at meiosis would indicate that the male diploid parent has a chromosome set that is homologous to the X genome of dallisgrass. Over 36,000 spikelets of dallisgrass were emasculated and dusted with pollen of 15 different diploid species (diploid species bearing I or J genomes were excluded). Only five (P. chaseanum, P. equitans, P. fasciculatum, P. notatum, and P. simplex) produced 2n+n hybrids with P. dilatatum. Meiotic chromosome behavior was similar in all hexaploid hybrids showing ca. 20 bivalents and 20 univalents. Results indicated a very low rate of 2n+n hybridization; none of the five diploid species possessed the X genome. Because several diploid species failed to hybridize with 5x dallisgrass, other methods should be attempted. Molecular markers specific for the X genome may help solve the question.

中文翻译：

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无融合生殖雀稗与二倍体雀稗物种的 2n+n 杂交

Common dallisgrass (Paspalum dilatatum) 是杂种起源的无融合生殖五倍体 (2n=5x=50)，具有不规则减数分裂和基因组式 IIJJX。I 和 J 基因组分别与二倍体 P. intermedium 和 P. jurgensii 同源，但 X 基因组的来源未知。X 基因组的成员可能具有具有特殊生物学意义的基因，包括控制无融合生殖的基因。常见的dallisgrass 与几个二倍体雀稗物种杂交，试图确定X 基因组的来源。由于普通的dallisgrass 是无融合生殖的，所有产生的杂种都将由未减数的卵(2n+n) 受精形成。任何在减数分裂时显示 30 个二价染色体的杂种都表明雄性二倍体亲本具有与红花草的 X 基因组同源的染色体组。36岁以上，将 000 株小穗草去雄并撒上 15 种不同二倍体物种的花粉（排除带有 I 或 J 基因组的二倍体物种）。只有五个（P.chaseanum、P.equitans、P. fasciculatum、P. notatum 和 P. simplex）与 P. dilatatum 产生 2n+n 杂种。所有六倍体杂种中的减数分裂染色体行为都相似，显示约。20 个二价和 20 个单价。结果表明 2n+n 杂交率非常低；五个二倍体物种都没有 X 基因组。由于一些二倍体物种未能与 5x dallisgrass 杂交，因此应尝试其他方法。X 基因组特异的分子标记可能有助于解决这个问题。fasciculatum、P. notatum 和 P. simplex) 与 P. dilatatum 产生 2n+n 杂种。所有六倍体杂种中的减数分裂染色体行为都相似，显示约。20 个二价和 20 个单价。结果表明 2n+n 杂交率非常低；五个二倍体物种都没有 X 基因组。由于一些二倍体物种未能与 5x dallisgrass 杂交，因此应尝试其他方法。X 基因组特异的分子标记可能有助于解决这个问题。fasciculatum、P. notatum 和 P. simplex) 与 P. dilatatum 产生 2n+n 杂种。所有六倍体杂种中的减数分裂染色体行为都相似，显示约。20 个二价和 20 个单价。结果表明 2n+n 杂交率非常低；五个二倍体物种都没有 X 基因组。由于一些二倍体物种未能与 5x dallisgrass 杂交，因此应尝试其他方法。X 基因组特异的分子标记可能有助于解决这个问题。应该尝试其他方法。X 基因组特异的分子标记可能有助于解决这个问题。应该尝试其他方法。X 基因组特异的分子标记可能有助于解决这个问题。