Apomixis and sexuality in diploid and tetraploid accessions of Brachiaria decumbens
Apomixis and sexuality in diploid and tetraploid accessions of Brachiaria decumbens
复制标题
斜卧臂形草二倍体和四倍体种质的无融合生殖和性行为
作者：
T. Naumova;M. D. Hayward;M. Wagenvoort
摘要：在两种环境下，对斜卧臂形草的二倍体和四倍体种质的减数分裂和无孢子胚囊以及孤雌胚胎发生和胚乳形成的初始步骤进行了研究，主要区别在于日长：初夏和深秋。二倍体和四倍体种质都是兼性无融合生殖体。二(ha)倍体显示出比四倍体(80%至95%)低得多的无融合生殖水平(10%至15%)。没有发现专性有性二倍体；因此，它们在自然种群中的出现情况是模糊的。有人认为，斜卧花的繁殖，与 Paniceae 部落的其他无性复合体一样，通常近似于二倍体-四倍体-(二)单倍体繁殖周期，不涉及三倍体。双单倍体是可繁殖的并且在自然界中存活下来。生殖结构的发育取决于环境。与初夏相反，秋季，许多减数分裂和无孢子胚囊在发育过程中退化，导致孤雌胚胎的比例显着减少。这种影响是否归因于日照长度或仅仅归因于年龄仍有待研究。无孢子胚囊与有性胚囊的比例在两个季节中相对稳定。
Abstract Meiotic and aposporous embryo sacs and the initial steps of parthenogenetic embryogenesis and endosperm formation were investigated in diploid and tetraploid accessions of Brachiaria decumbens in two environments, differing mainly in day length: early summer and late autumn. Both diploid and tetraploid accessions were facultative apomicts. Di(ha)ploids showed a much lower level of apomixis (10% to15%) than tetraploids (80% to 95%). No obligate sexual diploids were found; thus, their occurrence in natural populations is obscure. It is suggested that reproduction in B. decumbens, as in other agamic complexes of the Paniceae tribe, in general, approximates a diploid-tetraploid-(di)haploid reproductive cycle which does not involve triploids. The dihaploids were fertile and survived in nature. Development of the reproductive structures depended on the environment. In autumn, in contrast to early summer, many meiotic and aposporous embryo sacs degenerated during development, leading to a significant reduction in the proportion of parthenogenetic embryos. Whether this effect can be attributed to day length or simply to age remains to be investigated. The ratio of aposporous to sexual embryo sacs was relatively stable over the two seasons.