Castro Sílvia, Loureiro João, Santos Conceição, Ater Mohammed, Ayensa Garbiñe, Navarro Luis
Department of Plant Biology and Soil Sciences, Faculty of Science, University of Vigo, 36200 Vigo, Spain.
Ann Bot. 2007 Mar;99(3):507-17. doi: 10.1093/aob/mcl273. Epub 2007 Jan 11.
Oxalis pes-caprae is a widespread invasive weed in regions with a Mediterranean climate. In its native habitat (southern Africa) this species has been reported as heterostylous with trimorphic flowers and a self- and morph-incompatible reproductive system. In most of the areas invaded, only a pentaploid short-styled morphotype that reproduces mainly asexually by bulbils is reported, but this has only been confirmed empirically. This study aims to analyse the floral morph proportions in a wide distribution area, test the sexual female success, and explain the causes of low sexual reproduction of this species in the western area of the Mediterranean Basin.
Fifty-five populations of O. pes-caprae were sampled in the Iberian Peninsula and Morocco to evaluate the floral morph ratio and individual fruit set. In plants from a dimorphic population, hand-pollination experiments were performed to evaluate the effect of the pollen source on pollen tube growth through the style. The ploidy level and genome size of individuals of each floral morph were analysed using flow cytometry.
From the populations studied 89.1 % were monomorphic, with most of them containing the short-styled (SS) floral morph, and 10.9 % were dimorphic containing long-styled (LS) and SS morphs. In some of these, isoplethy was verified but no fruit production was observed in any population. A sterile form was also recorded in several populations. Hand-pollination experiments revealed that pollen grains germinated over recipient stigmas. In intermorph crossings, pollen tubes were able to develop and fruit initiation was observed in some cases, while in intramorph pollinations, pollen tube development was sporadic and no fruit initiation was observed. All individuals within each floral form presented the same DNA ploidy level: SS plants were pentaploid and LS and the sterile form were tetraploid.
The low or null sexual reproduction success of this species in the area of invasion studied seems related with the high frequency of monomorphic populations, the unequal proportion of floral morphs in dimorphic populations and the presence of different ploidy levels between SS and LS morphs. The discovery of the occurrence of an LS floral morph and a sterile form, whose invading capacity in these areas is as yet unknown, will be valuable information for management programmes.
酢浆草是地中海气候地区广泛分布的入侵杂草。在其原生栖息地（南非），该物种被报道为具有三型花的异型花柱植物，以及自交不亲和且形态不亲和的繁殖系统。在大多数入侵地区，仅报道了一种主要通过珠芽进行无性繁殖的五倍体短花柱形态类型，但这仅通过经验得到证实。本研究旨在分析广泛分布区域内的花形态比例，测试雌性有性繁殖成功率，并解释该物种在地中海盆地西部地区有性繁殖率低的原因。
在伊比利亚半岛和摩洛哥采集了55个酢浆草种群，以评估花形态比例和单个果实的结实情况。在一个二型种群的植株上进行了人工授粉实验，以评估花粉来源对花粉管通过花柱生长的影响。使用流式细胞术分析了每种花形态个体的倍性水平和基因组大小。
在所研究的种群中，89.1%为单型，其中大多数包含短花柱（SS）花形态，10.9%为二型，包含长花柱（LS）和SS形态。在其中一些种群中，验证了等频率现象，但在任何种群中均未观察到果实产生。在几个种群中还记录到了不育形态。人工授粉实验表明，花粉粒在受体柱头上萌发。在异型杂交中，花粉管能够发育，在某些情况下观察到果实起始，而在同型授粉中，花粉管发育是零星的，未观察到果实起始。每种花形态内的所有个体都呈现相同的DNA倍性水平：SS植株为五倍体，LS和不育形态为四倍体。
在所研究的入侵区域，该物种有性繁殖成功率低或无似乎与单型种群的高频率、二型种群中花形态比例不均以及SS和LS形态之间存在不同倍性水平有关。发现存在LS花形态和不育形态，其在这些地区的入侵能力尚不清楚，这将为管理计划提供有价值的信息。
