Self-incompatibility limits sexual reproduction rather than environmental conditions in an invasive water primrose.

Fruit-set and seed-set depend on environmental conditions and reproductive systems. They are important components of sexual reproductive success in plants. They also control the ecological success and adaptation of invasive plants within their non-native ecosystems. We studied which factors bring about fruit-set and seed-set in invasive populations of the aquatic plant Ludwigia grandiflora subsp. hexapetala. We analyzed fruit set and seed set in 37 populations growing under variable climatic conditions in Western Europe. Sub-samples of seven fruitful and fruitless populations were grown in common controlled conditions. We carried out self- and cross-pollinations, and measured the floral morphometry. Environmental conditions did not affect fruit-set and seed-set in-situ and in common controlled environments. Hand-pollinations showed that individuals from fruitful populations exhibited fruit and seed production whatever the pollen donor, whereas individuals from fruitless populations only did so when pollen came from fruitful populations. Floral morphometry evidenced the existence of two floral morphs that fully overlapped with fruitfulness, and individual incompatibility. Our results rebutted the hypothesis that environmental variations control fruit set and seed set in these invasive populations. We instead showed that fruit set and seed set were controlled by a heteromorphic reproductive system involving a self-incompatible and inter-morph compatible morph (long-styled morph), and a self- and inter-morph compatible reverse morph (short-styled morph). We collected morphs and fruit set records of this species worldwide and found the same relationship: fruitless populations were all composed only of individuals with long-styled floral morph. Our study constitutes the first evidence of a heteromorphic self-incompatible system in Ludwigia genus and Onagraceae family.

Aquatic and terrestrial morphotypes of the aquatic invasive plant, Ludwigia grandiflora, show distinct morphological and metabolomic responses.

In the context of expansion of invasive species, survival of invasive plants is conditioned by their ability to adapt. In France, the water primrose Ludwigia grandiflora, an aquatic invasive species, invades yet wet meadows, leading to a depreciation of their fodder value. Understanding its potential adaption is necessary to its management, strong differences between both morphotypes were expected. So morphological and metabolic responses to terrestrial environment were analyzed for aquatic and terrestrial morphotypes. All morphological and biomass variables were greater in the terrestrial morphotype than the aquatic morphotype, independent of conditions. In terrestrial condition, both morphotypes showed a high production of sugars in root tissues, especially in the terrestrial morphotype and both morphotypes produced a low level of amino acids in shoot tissues. All results demonstrate that the terrestrial condition seems a stressful situation for both morphotypes, which activates glycolysis and fermentation pathways to improve their survival under hypoxic stress. But, only the terrestrial morphotype has been able to adjust its metabolism and maintain efficient growth. In the future, a differential transcriptomic analysis will be carried out to confirm this result.