The Lulo (Solanum quitoense Lam.), an underutilized fruit crop originally from the Andes, is still widely unknown, however its delicious taste (The fruit has a citrus flavour, sometimes described as a combination of rhubarb and lime) and high nutrition values could soon see it as a high potential greenhouse crop in Central Europe, although production might be limited by seasonal fluctuations in day length due to its parentage.
Scientists at the Ecological-Botanical Garden, University of Bayreuth, studied Lulo’s reproductive development and yield in regard to seasonal photoperiod and supplemental lighting in winter (Scientia Horticulturae). Seeds were sown twice a year on 15 February and 20 June 2012 and grown under natural light conditions so that flowering started in summer (natural long-day) and winter (natural short-day), respectively. Lulo flower initiation and fruit set occurs throughout the year and timing is not significantly different between plants grown under long-day (natural, artificial) and those grown under short-day conditions. However, flower development is affected by photoperiod as first time from bud to fruit set and therefore harvest begin was accelerated at long-days.
The proportion of hermaphroditic flowers increased in natural, not artificial long-days probably due to higher light intensity. Summer blooming plants bore more fruits (15 fruits per plant) than winter blooming ones (10 fruits). Supplemental lighting in winter only increased fruit number to a comparable amount as in summer but not yield. Surprisingly, blooming and fruiting period was conspicuously longer when flowering started under natural conditions in winter and therefore lasted until spring. So regarding this whole blooming period total yield was even higher when plants were grown during winter without supplemental lighting. In conclusion, reproduction of Lulo plants is not restricted to a certain seasonal day length indicating that this crop is suitable for year-round fruit production under greenhouse conditions in Central Europe. Sowing twice a year ensures a year-round production. Long-days accelerated harvest and increased fruit number but not yield but artificial lighting in winter does not enhance yield compared to ambient light.