Amphicarpy in Trifolium argentinense: morphological characterisation, seed production, reproductive behaviour and life strategy

Abstract

Trifolium argentinense Speg. is an amphicarpic species that occurs naturally in native pastures of Rio Grande do Sul, southern Brazil. Amphicarpy is a rare mode of reproduction in which aerial and subterranean seeds are produced by the same individual. In the present paper, we compare morphology, anther number, pollen viability, seed production and mode of reproduction of T. argentinense flowers, and comment on the life strategy of the species. Plants grown from aerial seeds and from the regrowth of storage roots of aerial plants had longer stolons and a larger plant diameter than did those grown from subterranean plants. Plants grown from seeds were also taller than plants grown from storage roots. More resources were allocated to subterranean reproduction in plants of subterranean origin than in those of aerial origin. Aerial flowers produced more seeds, presented more anthers and produced more pollen grains than did the subterranean ones. T. argentinense is a versatile species, self- and cross-pollinated, consistent with the values of high polymorphism information content. T. argentinense adopts the ‘pessimistic strategy’ (early allocation of energy to large subterranean propagules), common in amphicarpic species when growing in disturbed habitats, such as the native pastures of Rio Grande do Sul, where intense grazing and trampling, as well as long seasonal dry spells, may periodically destroy the aerial plants, thus assuring survival by germination of subterranean seeds and regrowth of storage roots.

Genetic diversity assessed by microsatellite markers in the amphicarpic species Trifolium polymorphum Poir.

“…The PIC values, which reflect allelic diversity and frequency, were high, ranging from 0.62 (SSR TM0118) to 0.89 (SSR prs461, SSR TM0180, SSR TM0065 and SSR TM0406), with a mean of 0.84 (Table II), similar to the PIC variation between 0.52 to 0.86 in Uruguayan populations and as expected for a highly heterogeneous cross-pollinated species such as T. polymorphum ). Similar results were found for the T. argentinense, with PIC values between 0.66 and 0.93 (Conterato et al 2013), the Trifolium riograndense Speg, between 0.48 and 0.80 (Conterato et al 2012) andT. pretense, between 0.70 and0.86 (Dias et al 2008).…”

“…The subterranean flowers are obligatory cleistogamous with four to five anthers, while the aerial flowers with 10 anthers (Conterato and Schifino-Wittmann 2014) have been reported as being allogamous, self-compatible and that benefit from pollinators for seed production ). The other amphicarpic species of the genus, T. argentinense Speg, has been extensively studied in relation to seed dimorphism (Conterato et al 2010), seed production, morphology, reproductive biology and life strategy (Conterato et al 2013). During winter T. polymorphum is an important forage component of natural grasslands of Rio Grande do Sul (between 30ºS and 34ºS) due to its high palatability and good forage quality (Speroni and Izaguirre 2003).…”

“…Microsatellites, also known as SSR (Simple Sequence Repeats) markers, have gained considerable importance for their many desirable genetic attributes, including hypervariability, broad genomic distribution, co-dominant inheritance, reproducibility, multi-allelic nature and specific chromosomal location (Verma et al 2015), and for their wide use in analyzing genetic diversity , Conterato et al 2013, Dugar and Popov 2013, Njung'e et al 2016, Liang et al 2007, Sinha et al 2015, Swift et al 2016), plant breeding (Islam et al 2012, Tan et al 2014, phylogenetic studies (Kang et al 2015), among others.…”

Reproductive strategies and dimorphic seeds germination in Trifolium argentinense Speg., an amphicarpic species

“…T. argentinense is a plant that occur in a low frequence in the natural pastures of the southern half of Rio Grande do Sul, Uruguay and Argentina (BURKART, 1952) and combines two types of reproductive strategies: asexual propagation by regrowth of storage roots and sexual reproduction by two types of flowers: aerial and subterranean with distinct ecological functions. A third type of flower, produced at soil-surface has been observed, but the exact nature of this type of flower is unknown (CONTERATO et al, 2013). Vegetative propagation contributes mainly to the local population growth and preservation of the parental genotype.…”

“…Vegetative propagation contributes mainly to the local population growth and preservation of the parental genotype. In contrast, the aerial flowers allow dispersion of seeds over long distances, reduction of intra-specific competition and assure genetic diversity due to the preferential allogamy, while the cleistogamous subterranean flowers contribute to the population local growth (CONTERATO et al, 2013). The subterranean flowers of T. argentinense produce larger seeds, heavier and fewer in number than those of aerial flowers (CONTERATO et al, 2010), while those present more anthers, produce more pollen grains and more seeds than the subterranean ones.…”