Phytosanitary risks associated with exotic tuber crop production in Belgium

The increasing introduction of new exotic crops in Europe are an opportunity for growers to produce for niche markets. These new crops, as well as “forgotten” crops, are mainly grown and marketed outside the general, large-scale commercial agriculture. This local production, and its associated short food supply chain, obtain planting materials (seed, tubers, cuttings) and products from different sources. The phytosanitary status of these materials is very rarely checked. Entry and spread of possible plant pathogens and pests could pose a threat to traditional crops, besides hampering the cultivation of the new crops. Especially when planting material is obtained from non-European countries, phytosanitary risks can be high. We present the first results of a project focusing on viruses and nematodes – both holding a high potential of being introduced without being noticed - in yacon (Smallanthus sonchifolius), ulluco (Ullucus tuberosus), sweet potato (Ipomoea batatas), crosne (Stachys affinis), mashua (Tropaeolum tuberosum), and oca (Oxalis tuberosa) as new crops, and Jerusalem artichoke (Helianthus tuberosus) as a forgotten crop in Belgium. Together with classic detection techniques, HTS is used to conduct an unprejudiced mapping of the presence of high risk viruses, particularly in starting material. After one year of survey, including an evaluation of tubers being traded through the internet, a multitude of viruses were detected in all of the included tuber crops. The results are still too preliminary to make a statement on the phytosanitary impact of these viruses, yet, there is ample of evidence that eg. sweet potato chlorotic stunt virus (SPCSV), a regulated Q pathogen, is definitely present in some of the sweet potato starting material. In addition, the fact that viruses are so numerous in some of these tubers indicates that not much attention is paid to their presence when trading and growing these crops. At least one other virus, Physostegia chlorotic mottle virus (PhCMoV) drew our attention, since it is a relatively new virus in our region and has been reported to induce serious disease symptoms in tomato and pepper. No nematodes of major concern were found in tubers from the field nor in planting material. However, we detected Pratylenchus species in several samples. Although none of them have a quarantine status and all are commonly found in Belgium, attention should be paid to P. penetrans, the most damaging species.
In the second year of this study, more attention will go to the potential presence of novel viruses, as well as to an assessment of the phytosanitary risks that all of the detected viruses represent.