Pollen:ovule ratio and its relationship with other floral traits in Papilionoideae (Leguminosae): an evaluation with Argentine species

Abstract

The pollen:ovule ratio (P/O) has traditionally been used as a rough estimator of plant breeding systems. It has been shown that plant breeding systems are associated with particular floral traits. In this study, we determined the P/O in 21 Leguminosae species from Argentina and explored relationships between P/O and taxonomic position, flower size, floral rewards, pollen presentation and pollination mechanisms. According to the results, 15 out of the 21 species classified were obligate xenogamous, although some of them have been recorded as facultative xenogamous in previous studies. There was a significant effect of taxonomic position (genus), reward type and pollination mechanism on P/O. Species offering only nectar as a floral reward (which were species with a brush mechanism) had a significantly lower P/O than species offering pollen or pollen and nectar. Species with the brush pollination mechanism had the lowest P/O, while species with valvular and pump mechanism had the highest P/O. However, pollen presentation (primary and secondary) and flower size did not have a significant effect on P/O. Our results demonstrate that P/O variability is determined by taxonomic position and pollination mechanism in this plant group.

Pollen: ovule ratio and its relationship with other reproductive traits in some <em>Passiflora</em> species (Passifloraceae)

“…(Ortega-Olivencia & al., 1997) but not in 21 papilionoid legumes (Etcheverry & al., 2012).P/O ratio was not correlated with stigma area in the Passiflora species analysed, perhaps because stigma area was not so different between them. On the contrary, P/O ratio was inversely related to the stigmatic area in two species of Stylidaceae and eight species from three genera of Proteaceae (Cruden, 1997).…”

“…Instead, a tendency to xenogamy or autogamy within various taxa at different levels (genus or tribe) of Polemoniaceae (in which P/O ratio is a good predictor of the breeding system) was perceived by Plitmann and Levin (1990). P/O variations were associated to genus but not to tribe in 21 papilionoid Legumes (Etcheverry & al., 2012). Jürgens & al (2002) suggested that taxonomy is indirectly related with P/O as a consequence of the combination of features typical of each taxonomic group.…”

“…Rather than breeding system, in several taxa P/O ratio reflects better pollination mechanism (Galloni & al., 2007) or pollination efficiency (Choteau & al., 2006). P/O ratio was significantly associated with pollination mechanism in species with unknown breeding system (López & al., 1999) and in 21 xenogamous legumes (Etcheverry & al., 2012). Lower P/O ratios usually coincide with precise or highly specialized pollen transfer mechanisms (Small, 1988;Jürgens & al., 2002;Choteau & al., 2006).…”

“…P/O ratio has further been explored in relation to sexual system (Lindsey, 1982;Jürgens & al., 2002;Choteau & al., 2006), pollination system (Plitman and Levin, 1990;Götzenberger & al., 2008), life form (Cruden, 1977;Small, 1988;Jürgens & al., 2002), seed mass (Götzenberger & al., 2006) and floral size (Etcheverry & al., 2012), among other parameters (see Ortega Olivencia & al., 1997). P/O ratio has not been examined in Passiflora L. yet.…”

Reproductive Ecology of Birdville Indigo, Indigofera Linnaei Ali. (Fabaceae)

“…Lopez et al (1999) recorded explosive pollination mechanism with highest pollen-ovule ratios in certain genera of the Fabaceae such as Cytisus, Pterospartum, Teline, Ulex, Stauracanthus and Cytisophyllum. Etcheverry et al (2012) noted that the Fabaceae plants which they studied with explosive pollination mechanism had intermediate pollen-ovule ratios. Padmavathi et al (2012) reported that Indigofera barberi with explosive pollination mechanism had intermediate pollenovule ratio.…”