Large scale propagation and in vitro weaning for the restoration of Viola palustris to support assisted colonisation of a threatened butterfly

Abstract The distribution and abundance of Boloria selene (small pearl-bordered fritillary butterfly, SPBF) declined over recent decades in many parts of the UK. Availability of food plants, especially marsh violet (Viola palustris), for the caterpillars of the SPBF has been identified as one of the major causes of this decline. To achieve augmentation of existing colonies and develop new populations of SPBF large numbers of marsh violet propagules were required specifically to feed the larvae. The main objectives of the study were to produce thousands of good quality marsh violet propagules to restore selected habitats in the Heart of Durham, Northern England, using in vitro methods. Preliminary trials showed that in vitro multiplication of seedlings from wild collected seeds through conventional agar-based cultures was lengthy, expensive and turned out to be a non-viable route to achieve the objectives. This study explored the potential of bioreactor-based cloning and cost-effective one step rooting and weaning. Robust propagules, ready for transplantation following rapid propagation and one step rooting and weaning in vitro, were raised in a plug system for transplantation and establishment under field conditions. This was achieved by using simple and cost-effective methods to support the large-scale restoration exercise using 14,000 propagules. Application of high throughput micropropagation and low cost one step weaning systems for time-bound conservation and restoration projects are discussed in detail. This research highlights the important role of in vitro methods to support integrated biodiversity conservation of a native larval host plant and threatened butterfly.