Interspecific hybrids between Paspalum plicatulum and P. oteroi: a key tool for forage breeding

ABSTRACT Grama-tio-pedro (Paspalum oteroi Swallen) is a rare stoloniferous grass of the Plicatula group of Paspalum, well adapted to continuous grazing in areas subject to seasonal flooding in the Pantanal region, in central western Brazil. The species is a facultative apomictic (asexual reproduction by seed) tetraploid, sporadically cultivated on Pantanal farms, propagated either by cuttings or seed. Due to its potential for extensive cultivation and forage quality, Grama-tio-pedro appears as a candidate for genetic improvement within the Plicatula group through plant breeding. We used a colchicine-induced sexual autotetraploid genotype of P. plicatulum Michx. to obtain interspecific hybrids using the apomictic species, P. oteroi, as pollen donor. The very similar meiotic chromosome behavior observed in both parents, with main quadrivalent and bivalent associations, suggested that P. oteroi is a natural autotetraploid. The hybrids showed less irregular meiotic behavior with fewer quadrivalents and more bivalents than either parent. Fertility among interspecific hybrids varied from complete sterility in some of them to seed productions in others that were approximately twice as much as for either parent. The great variability of seed set performance may well be a drastic genetic consequence of joining two homologous chromosome sets of P. plicatulum together with two homologous sets of P. oteroi that, in turn, have some homeology between them. Most hybrids reproduce by sexual means, thus, they could be used as female parents in backcrosses and in crosses with other species of the Plicatula group for interspecific gene transferring in breeding programs.

摘要 格拉萨-蒂奥-佩德罗（Grama-tio-pedro，学名：Paspalum oteroi Swallen）是隶属于雀稗属（Paspalum）褶叶雀稗组（Plicatula group）的稀有匍匐茎草本，对巴西中西部潘塔纳尔（Pantanal）地区季节性淹水生境下的连续放牧具有极强适应性。该物种为兼性无融合生殖（facultative apomictic，即通过种子进行无性繁殖）四倍体，偶在潘塔纳尔地区的农场中种植，可通过扦插或种子两种方式繁殖。鉴于其具备规模化种植潜力与优良饲用品质，格拉萨-蒂奥-佩德罗成为褶叶雀稗组内通过植物育种开展遗传改良的候选物种。本研究以秋水仙素诱导获得的有性生殖同源四倍体褶叶雀稗（Paspalum plicatulum Michx.）基因型为材料，以无融合生殖物种奥氏雀稗（Paspalum oteroi）作为花粉供体，成功获得种间杂种。两个亲本均表现出以主要四价体与二价体联会为特征的高度相似减数分裂染色体行为，这表明奥氏雀稗为天然同源四倍体。与任一亲本相比，杂种的减数分裂行为异常程度更低，四价体数量更少且二价体数量更多。种间杂种的育性差异显著，部分个体完全不育，其余个体的种子产量约为任一亲本的两倍。座果率所表现出的高度变异，很可能是将褶叶雀稗的两套同源染色体与奥氏雀稗的两套同源染色体相结合所产生的剧烈遗传后果——二者的同源染色体之间存在一定的部分同源性（homeology）。多数杂种通过有性方式繁殖，因此可作为母本用于回交，或与褶叶雀稗组的其他物种进行杂交，以实现育种计划中的种间基因转移。