Kovalsky I Evelin, Roggero Luque Juan M, Elías Gabriela, Fernández Silvia A, Solís Neffa Viviana G
Instituto de Botánica del Nordeste (UNNE-CONICET), CC 209, 3400, Corrientes, Argentina.
Facultad de Ciencias Exactas y Naturales y Agrimensura (UNNE), Corrientes, Argentina.
J Plant Res. 2018 Jan;131(1):77-89. doi: 10.1007/s10265-017-0974-9. Epub 2017 Aug 22.
Triploids can play an important role in polyploid evolution. However, their frequent sterility is an obstacle for the origin and establishment of neotetraploids. Here we analyzed the microsporogenesis of triploids (x = 7) and the crossability among cytotypes of Turnera sidoides, aiming to test the impact of triploids on the origin and demographic establishment of tetraploids in natural populations. Triploids of T. sidoides exhibit irregular meiotic behavior. The high frequency of monovalents and of trivalents with non-convergent orientations results in unbalanced and/or non-viable male gametes. In spite of abnormalities in chromosome pairing and unbalanced chromosome segregation, triploids are not completely sterile and yielded up to 67% of viable pollen. Triploids that originated by the fusion of 2n × n gametes of the same taxon showed more regular meiotic behavior and higher fertility than triploids from the contact zone of diploids and tetraploids or triploids of hybrid origin. The reproductive isolation of T. sidoides cytotypes of different ploidy level is not strict and the 'triploid block' may be overcome occasionally. Triploids of T. sidoides produce diploid and triploid progeny suggesting that new generations of polyploids could originate from crosses between triploids or from backcrosses with diploids. The capability of T. sidoides to multiply asexually by rhizomes, would enhance the likelihood that a low frequency of neopolyploids can be originated and maintained in natural populations of T. sidoides.
三倍体在多倍体进化中可发挥重要作用。然而，它们频繁的不育性是新四倍体起源和建立的一个障碍。在此，我们分析了三倍体（x = 7）的小孢子发生以及西番金莲不同细胞型之间的可杂交性，旨在测试三倍体对自然种群中四倍体起源和种群建立的影响。西番金莲三倍体表现出不规则的减数分裂行为。单价体和方向不收敛的三价体的高频率出现导致雄性配子不平衡和/或无活力。尽管染色体配对异常和染色体分离不平衡，但三倍体并非完全不育，可产生高达67%的有活力花粉。由同一分类群的2n×n配子融合产生的三倍体比来自二倍体和四倍体接触区的三倍体或杂种起源的三倍体表现出更规则的减数分裂行为和更高的育性。西番金莲不同倍性水平的细胞型之间的生殖隔离并不严格，“三倍体障碍”可能偶尔会被克服。西番金莲三倍体产生二倍体和三倍体后代，这表明多倍体的新一代可能起源于三倍体之间的杂交或与二倍体的回交。西番金莲通过根状茎进行无性繁殖的能力，将增加在西番金莲自然种群中低频率新多倍体能够起源并维持的可能性。
