Gemmorhizogenesis in poysean (Euphorbia × lomi Rauh): the production of 'likely-asexuate' vivipary offsprings

Poysean (Euphorbia × lomi Rauh) is a natural hybrid of E. milii Des Moulins × E. lophogona Lamarck. This hybrid has a high tolerance to drought and high temperature and the ability to withstand long periods in the complete absence of water. In its native environment, Madagascar, it colonizes wide arid areas and this occurs both due to its stress tolerance and its ability to produce ‘likely-asexuate’ vivipary offsprings (aboveground LAVOs) from the aerial parts. These propagules show completely differentiated aboveground organs and root primordial or sometimes radicles when still standing on their mother plant. However, no information is available about the ability of this hybrid to produce such offsprings. In the present work, we studied the production of aboveground LAVOs of a cultivar of E. × lomi, namely the Thailand’s cultivar ‘Porn ying yai’, in a 2-years pot experiment with 2 contrasting growing media (coconut fibre/perlite, CCP, or peat/perlite, PTP) under greenhouse conditions. In total, 24 mother plants per year per substrate were grown, propagules were counted, and length and weight measured and divided per class of quality, corresponding to a length class (1^st class below 5.0 cm, 2^nd class between 5.1 and 10.0 cm, and 3^rd class above 10.1 cm). Thus, propagules were planted to check for their vitality. Plants grown in PTP yielded 2.3-fold more propagules than CCP. However, such difference solely occurred for 1^st class propagules, whereas no differences were found for 2^nd and 3^rd class propagules between growth substrates. Since the pots were widely fertirrigated, and thus not limited by water or nutrient availability, this suggests that the chemical or other traits of the growing media mostly modulate the conditions for the above-ground LAVOs induction rather than their growth. Since this plant has low maintenance needs and can withstand water lack and high temperature, these results have implication in urban environments, where colonization of green areas could occur after planting without anthropic intervention.