短枝木麻黄不同亲缘关系的亲本交配和花粉竞争对子代适应性的影响

According to published reports, studies on effects of inbreeding, outbreeding and pollen competition on progeny fitness were mainly focused on naturally distributed herbaceous and shrub plant under population level, but studies on distance and close hybridization and pollen competition in tree plant, especially in introduced tree species under different genetic distance are not well documented. In this study, five different distances and close hybridization experiments in casuarina will be conducted, including inter-specific hybridization within the Casuarina genus, inter-provenance hybridization within Casuarina. equisetifolia species, inter-family hybridization within provenance, inbreeding within family and selfing within monoecious individuals with an aim to determine the effects of outbreeding and inbreeding on progeny fitness. Pollen originated from male trees with different genetic distance will be collected and mixed (iner-specific pollen be mixed two-by-two or triple mixture, intra-specific, including outcrossing pollen, inbreeding pollen and selfing pollen be mixed two-by-two), then be pollinated on the same stigmas to study the effects of pollen competition on progeny fitness. Paternity analysis will be conducted on progenies obtained from pollen competition using SSR molecular marker technique, to reveal competition relationship of inter-specific and intra-specific pollen on the same stigmas. At the same time, pollen germination rate will be measured using in vitro germination method, to indicate effects of pollen viability and speed of pollen tube growth on competitive ability. Study results will offer beneficial theoretical and technical support for cross breeding, construction and genetic management of seed orchard, and developing breeding strategy in casuarinas and other tree species.

已发表的文献表明，植物远、近缘交配和花粉竞争对子代适应性影响的研究主要集中在天然分布的草灌植物的种群水平上，在乔木植物、特别是非天然分布的人工栽培树种上同时开展不同亲缘关系的亲本交配和花粉竞争的研究还未见报道。本项目以短枝木麻黄为主要研究对象，开展木麻黄种间、种源间、家系间、家系内和个体内5个层次亲缘关系的亲本交配试验，研究其对子代适应性的影响；收集不同亲缘关系的花粉，进行种间花粉两两或多重混合，种内的异交、近交和自交花粉两两混合，在相同雌花上进行控制授粉，研究花粉竞争对子代适应性的影响；利用SSR分子标记技术对花粉竞争获得的子代进行父本分析，研究不同亲缘关系花粉在同一柱头上的竞争关系和竞争规律；同时利用离体萌发法比较各亲缘关系花粉的萌发率和萌发速度，研究花粉活力和萌发速度对花粉竞争能力的影响。研究结果将对木麻黄和其它树种的杂交育种、种子园营建和育种策略的制定有重要的理论价值与实践意义。

在本研究中，首先开展了短枝木麻黄的生殖生物学和繁殖系统研究和木麻黄EST-SSR分子标记引物的筛选和优化；在此基础上，通过开展木麻黄不同亲缘关系的亲本交配试验，研究其对子代适应性的影响；通过开展不同亲缘关系的花粉混合后在相同雌花柱头上争夺授精机会的试验，研究花粉竞争对子代适应性的影响。研究结果表明，短枝木麻黄在自由授粉的状态下存在严重的传粉限制；木麻黄种内和种间的杂交亲和性没有显著差异，说明木麻黄种间不存在生殖隔离，但短枝木麻黄雌雄同株的自交子代表现出严重的近交衰退现象。为了开展花粉竞争中获得子代的父本分析，筛选和优化了12对具有高多态性的EST-SSR引物。远缘和近缘的亲本交配对子代的座果率、结实率、球果结籽数、千粒重、发芽率等子代适应性有显著的影响，也对子代小苗的苗高、胸径、保存率等生长性状有显著影响。极远缘（种间）杂交和极近缘（近交和自交）交配都对子代的适应性和生长性状有不利影响，而同一种内的不同种源间的杂交获得的子代在适应性和生长性状上都表现最好。不同亲缘关系的花粉竞争对子代的适应性和父本的生殖成功也有显著的影响，亲缘关系较远（种间）的花粉竞争获得的子代在种子萌发率、小苗的保存率和生长性状等优于亲缘关系较近（近交和自交）的花粉竞争获得的子代。基于EST-SSR分子标记的父本分析表明，花粉竞争中亲缘关系适中（种源间杂交）的花粉比亲缘关系极远（种间杂交）和极近（近交和自交）的花粉具有更高的竞争力。木麻黄通过花粉竞争可以淘汰掉部分的远缘或极近缘的花粉，使其不能通过雌花授精产生适应性低的子代，从而达到更高的生殖成功率的目的。