Tetraploid Spathiphyllum wallisii plants: do they have added value?

Mitotic chromosome doubling was performed on 7 different genotypes of Spathiphyllum wallisii. We analysed the morphological, anatomical and physiological characteristics of the tetraploids obtained in comparison to their diploid counterparts. Stomatal density was negatively correlated with an increased ploidy level, while stomatal size increased in polyploids. Leaves of tetraploid Spathiphyllum plants were more ovate and thicker. Similar changes were seen in the spathum of the inflorescence. In addition, a more cylindrical spadix and a thicker but shorter flower stalk were observed. Biomass production of the tetraploids was reduced, as expressed by a lower total dry weight. In general tetraploids produced also fewer shoots and leaves compared to their diploid progenitors. To study the impact of growing conditions, both diploid and tetraploid plants were grown under two different temperature conditions, DIF0: day and night temperature 20°C and DIF7: day temperature = 20°C and night temperature = 13°C. The differences in leaf and flower morphology between diploid and tetraploid plants remained similar independent from the growing conditions. However, both diploid and tetraploid plants cultivated at DIF0 had thicker and larger leaves, a higher dry weight and a thicker spathum compared to those growing at DIF7. Plants had also more flowers and flowered earlier when growing at DIF0. Under in-house conditions, tetraploid Spathiphyllym plants were more resistant to drought stress compared to diploid plants. After 15 days of drought stress, diploids wilted, while the tetraploids showed almost no symptoms. Measurements of stomatal resistance, leaf water potential, relative water content and proline content indicated that the tetraploid genotypes were more resistant to drought stress compared with the diploids.