Baek You Soon, Royer Suzanne M, Broz Amanda K, Covey Paul A, López-Casado Gloria, Nuñez Reynaldo, Kear Philip J, Bonierbale Merideth, Orillo Matilde, van der Knaap Esther, Stack Stephen M, McClure Bruce, Chetelat Roger T, Bedinger Patricia A
Department of Biology, Colorado State University, Fort Collins, Colorado 80523-1878, USA.
Department of Plant Biology, Cornell University, Ithaca, New York 14853, USA.
Am J Bot. 2016 Nov;103(11):1964-1978. doi: 10.3732/ajb.1600356. Epub 2016 Nov 18.
Interspecific reproductive barriers (IRBs) often prevent hybridization between closely related species in sympatry. In the tomato clade (Solanum section Lycopersicon), interspecific interactions between natural sympatric populations have not been evaluated previously. In this study, we assessed IRBs between members of the tomato clade from nine sympatric sites in Peru.
Coflowering was assessed at sympatric sites in Peru. Using previously collected seeds from sympatric sites in Peru, we evaluated premating prezygotic (floral morphology), postmating prezygotic (pollen-tube growth), and postzygotic barriers (fruit and seed development) between sympatric species in common gardens. Pollen-tube growth and seed development were examined in reciprocal crosses between sympatric species.
We confirmed coflowering of sympatric species at five sites in Peru. We found three types of postmating prezygotic IRBs during pollen-pistil interactions: (1) unilateral pollen-tube rejection between pistils of self-incompatible species and pollen of self-compatible species; (2) potential conspecific pollen precedence in a cross between two self-incompatible species; and (3) failure of pollen tubes to target ovules. In addition, we found strong postzygotic IRBs that prevented normal seed development in 11 interspecific crosses, resulting in seed-like structures containing globular embryos and aborted endosperm and, in some cases, overgrown endothelium. Viable seed and F hybrid plants were recovered from three of 19 interspecific crosses.
We have identified diverse prezygotic and postzygotic IRBs that would prevent hybridization between sympatric wild tomato species, but interspecific hybridization is possible in a few cases.
种间生殖障碍（IRBs）常常会阻止同域分布的近缘物种间杂交。在番茄进化枝（茄属番茄组）中，此前尚未评估过自然同域分布种群间的种间相互作用。在本研究中，我们评估了来自秘鲁9个同域分布地点的番茄进化枝成员间的种间生殖障碍。
在秘鲁的同域分布地点评估花期重叠情况。利用此前从秘鲁同域分布地点收集的种子，我们在共同园圃中评估了同域分布物种间的交配前合子前障碍（花形态）、交配后合子前障碍（花粉管生长）以及合子后障碍（果实和种子发育）。在同域分布物种间的正反交中检测花粉管生长和种子发育情况。
我们证实了秘鲁5个地点的同域分布物种花期重叠。我们在花粉 - 雌蕊相互作用过程中发现了三种交配后合子前种间生殖障碍类型：（1）自交不亲和物种的雌蕊与自交亲和物种的花粉间的单侧花粉管排斥；（2）两个自交不亲和物种杂交中潜在的同种花粉优先；（3）花粉管无法靶向胚珠。此外，我们发现了强烈的合子后种间生殖障碍，在11个种间杂交中阻止了正常种子发育，导致形成含有球形胚和败育胚乳的种子状结构，在某些情况下还有过度生长的内皮层。从19个种间杂交中的3个中获得了可育种子和F1杂交植株。
我们鉴定出了多种合子前和合子后种间生殖障碍，这些障碍会阻止同域分布的野生番茄物种间杂交，但在少数情况下种间杂交是可能的。
