The development, validation and application of a crop growth model to assess the potential of Solanum sisymbriifolium as a trap crop for potato cyst nematodes in Europe B.G.H. Timmermans *, J. Vos, T.J. Stomph Chair Crop and Weed Ecology, Plant Sciences Group, Wageningen University and Research Centre, P.O. Box 430, 6700 AK Wageningen, The Netherlands 1. Introduction In recent years Solanum sisymbriifolium (Lam.) has been suggested as a trap crop for potato cyst nematodes in The Netherlands (Scholte, 2000a,b; Scholte and Vos, 2000). Research has focused on germination (Timmermans et al., 2007c), field performance (Timmermans et al., 2007a,b) and effects on hatching of potato cyst nematodes (Scholte and Vos, 2000; Timmermans et al., 2006). The current use of S. sisymbriifolium is not as a cash crop itself, but strictly as a nematode control measure. Previous research determined a correlation between above-ground dry matter of the crop, root length density in the top 40 cm of the soil (in which more than 90% of the cyst are located, Been and Schomaker, 1999) and nematode hatching (and thus cyst deple- tion) (Timmermans et al., 2007b). It can be deduced from this relation that a crop of 700 g m 2 above-ground dry matter would have sufficient roots to remove 75% of all cysts. In the current study this above-ground crop dry mass was used as the minimum required for S. sisymbriifolium to be effective as a trap crop. In The Netherlands, crops of S. sisymbriifolium can be grown successfully, but it was not possible to grow S. sisymbriifolium crops in early spring due to a high base temperature for germination. Further- more, growth of S. sisymbriifolium crops sown later than the beginning of August was very variable (Timmermans et al., Field Crops Research 111 (2009) 22–31 ARTICLE INFO Article history: Received 4 April 2008 Received in revised form 20 August 2008 Accepted 13 October 2008 Keywords: Climatic gradient Europe Globodera pallida G. rostochiensis modelling Simulation ABSTRACT Solanum sisymbriifolium (Lam.), a plant that was introduced as a trap crop for potato cyst nematodes, shows strong temperature limitation of its growth. Previous research indicated that the crop needs to accumulate at least 700 g m 2 dry matter to achieve sufficient nematode control. In that context, three functionally different geographical zones can be distinguished: (i) a zone with insufficient growth, independent of sowing time, (ii) a zone with potentially sufficient growth if the crop is allowed to grow for the whole growing season, and (iii) a zone with sufficient growth early or late in the growing season, opening the option to combine cultivation of the trap crop with another crop in the same year. The aim of the current research was to delimit these zones for western and central Europe, by developing a model enabling simulation of the potential growth of S. sisymbriifolium in 64 locations between Scandinavia and Spain and between the UK and Hungary. A LINTUL type crop growth model for potential growth was adapted to S. sisymbriifolium. Adaptations regarded particularly the relative growth rate of the leaf area, the specific leaf area, and the radiation use efficiency, that were made temperature dependent using experimental data. Furthermore, the leaf death rates were modelled as limited by light availability in the canopy. The model was calibrated with field data from an experiment in 2002, and validated on field experiments in 2001, 2003 and 2004, resulting in a root mean square error (RMSE) of 118.1 g m 2 crop dry matter and a mean deviation (MD) of 15.9 g m 2 for the validation data. Simulations were done for the 64 sites, using weather data from 1996 to 1999, and the studied area was divided in the three zones (i, ii and iii) as described above. In all regions the crop could reach the required minimum size, although barely so in Scandinavia and the north of the United Kingdom. Zone (ii) included the south of the United Kingdom and Sweden, The Netherlands, Germany, Belgium and the north of France. Zone (iii) included the rest of France, Spain, Portugal, Italy, and Hungary; here temperature and radiation suffice for the crop to reach its required minimum size in only part of the growing season, leaving space for an other (main) crop in the same season, at least in the absence of water limitations. ß 2008 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +31 343 523 865; fax: +31 343 515 611. E-mail address: b.timmermans@louisbolk.nl (B.G.H. Timmermans). Contents lists available at ScienceDirect Field Crops Research journal homepage: www.elsevier.com/locate/fcr 0378-4290/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2008.10.002