Microsatellite Markers Confirm Self‐Pollination and Autogamy in Wild Populations of Vanilla mexicana Mill. (syn. V. inodora) (Orchidaceae) in the Island of Guadeloupe

Abstract

The study aimed at evaluating the mating system of Vanilla mexicana (Orchidaceae) in natural populations in the island of Guadeloupe. A total of 132 V. mexicana samples were collected from 12 sites in Guadeloupe (Basse-Terre). Five other samples coming from Martinique and Mexico completed our analyses. Reproductive biology experiments excluding pollinators with bagged flowers revealed 53.9% fruit set, a value identical to the natural fruit set measured in the populations. These results suggested that V. mexicana, unlike most Vanilla species, was reproducing by self-pollination and autogamy. Due to lack of specific DNA markers for V. mexicana, microsatellite markers, previously developed in other Vanilla species, were used for the genetic analyses. Only 6 out of the 33 markers tested were transferable and polymorphic in V. mexicana. A panel of 51 V. mexicana samples genotyped with 3 polymorphic loci was finally retained for Guadeloupe population genetic analyses. A heterozygote deficiency was detected, and the selfing rate was estimated to 74%. These results confirmed the reproductive biology results as self-pollination and autogamy were the most likely explanation for this deficit. Results were compared to those from allogamous wild Vanilla species and discussed in the light of suggested existence of a pollinator for V. mexicana in other areas (Mexico).

Drivers of population divergence and species differentiation in a recent group of indigenous orchids (Vanilla spp.) in Madagascar

“…The levels of genetic diversity were relatively high for 20 populations out of the 23 (0.42 < He < 0.84, 3.45 < Ar < 7.65), with an overall low genetic differentiation (FST = 0.19). These results are compatible with what was expected for Vanilla species, which are long‐lived thanks to vegetative growth, mostly allogamous (Gigant et al., 2014; Gigant, De Bruyn, et al., 2016; Gigant, Rakotomanga, et al., 2016; Petersson, 2015), with most likely bee‐mediated pollination and suspected zoochorous seed dispersion (by bees or bats) (Gigant et al., 2011; Gigant, De Bruyn, et al., 2016). These results also agree with expectations for orchids species for which high He ranging from 0.3 up to 0.9 is reported (Chen et al., 2014; Soliva & Widmer, 2003; Stone et al., 2012; Swarts et al., 2009).…”

Vanilla beyond Vanilla planifolia and Vanilla × tahitensis: Taxonomy and Historical Notes, Reproductive Biology, and Metabolites

“…Species may exhibit different mating systems. To assess the breeding system of Vanilla species, different tests have been applied, such as (i) agamospermy, in which the pollen content was removed before the complete development of the flowers, as performed with V. bicolor flowers [ 33 ]; (ii) spontaneous self-pollination or autogamy experimentation, in which pre-anthesis buds are bagged for avoidance of a pollinator visit, using insect-proof bags; (iii) open pollination or control treatment, in which flowers remain under natural conditions and natural fruit set can be observed; (iv) manual self-pollination, in which flowers are pollinated with their own pollen, in order to investigate self-compatibility; (v) manual geitonogamy, which involves the pollen of a flower fertilizing another flower from the same parent plant or from a clone; (vi) manual cross-pollination, in which flowers are previously emasculated and then manually pollinated with the pollen from another individual; and (vii) natural cross-pollination, with emasculated flowers left under natural conditions [ 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 ]. Among these treatments, manual self-pollination and manual cross-pollination are usually more successful in fruit production and exhibit high fruit sets.…”

“…The following Vanilla species are thought to be spontaneous self-pollinators due to their high fruit set under natural conditions: V. martinezii (up to 53% in a clone) [ 48 ], V. guianensis (78%) [ 49 ], V. Mexicana (syn. V. inodora ) (53.9%) [ 38 ], V. bicolor (42.5 and 71%) [ 33 , 49 ], V. savannarum , V. griffithii [ 50 ], and V. palmarum (70.3%) [ 49 , 50 ]. Different mechanisms were proposed by researchers to explain spontaneous self-pollination in Vanilla flowers: (i) the leaking of an abundant stigmatic fluid, which promotes its contact with the pollen grains, and induces the germination of pollen tubes [ 33 , 60 ]; (ii) the presence of a reduced or dehydrated rostellum that facilitates the encounter of pollen and stigma [ 33 ]; and (iii) the contact of the growing anther and stigma in early anthesis, as observed in V. guianensis [ 49 ].…”

The Leafless Vanilla Species-Complex from the South-West Indian Ocean Region: A Taxonomic Puzzle and a Model for Orchid Evolution and Conservation Research

“…There are, however, species that bloom throughout the year or during several months like V. inornata [32], V. rivasii [44] or V. bicolor [42]. Although some Vanilla species have an unusual high natural fruit set (>40%) (Figure 4), which suggests self-pollination [20,42,45,46], most are pollinator-dependent due to the presence of the rostellum membrane separating the female and male parts of the flower [10,19,21,23]. Some mechanisms were reviewed by Gigant et al, to explain self-pollination: it may be caused by either stigmatic leak and/or the presence of a dehydrated or reduced rostellum, or agamospermy (e.g., V. bicolor and V. palmarum), but some spontaneous self-pollinations remain unexplained (e.g., V. planifolia and V. chamissonis) [18].…”

“…Although only V. planifolia is of major economic interest on the global scale, the other species represent an important gene pool for the future breeding programs of commercial varieties. Indeed, other species have interesting traits that V. planifolia may not always have, such as high fruit set [42], self-pollination [20,42,46], resistance to diseases [59,64,73], medicinal proprieties [10,23,70,74] and adaptation to drought [10,23].…”