Screening for TBV-resistance in seedling populations of Tulipa L

Tulip breaking virus (TBV) threatens bulb and flower production of tulips seriously. Breeding for resistance as a tool to prevent this disease resulted already in a screening test at clonal level and different levels of resistance were detected. Clonal tests are performed under greenhouse conditions after inoculation by viruliferous aphids. By using several bulbs of a genotype an accurate level of resistance can be determined. All cultivars of T. gesneriana tested were susceptible, but partial and even absolute resistance was found in T. fosteriana cultivars. To introduce resistance from T. fosteriana in the T. gesneriana assortment interspecific crosses were made. To select TBV resistant hybrids efficiently, a screening test, applicable at individual seedlings, is described. To test individual seedling selection, an incomplete diallel was made between the susceptible T. gesneriana cultivars 'Christmas Marvel', 'Kees Nelis' and 'Lustige Witwe', the partial resistant T. fosteriana cultivars 'Juan' and 'Madame Lefeber' and the absolute resistant T fosteriana cultivars 'Cantata' and 'Princeps'. Individual seedlings were inoculated using viruliferous aphids in the first, third or fifth year after sowing. Six weeks after inoculation, leaves were tested for TBV by ELISA. All seedlings were grown till maturity and the occurrence of breaking symptoms in the flower was monitored. Individual resistant seedlings could be selected. However, susceptible plants can occur (escapes) between the selected plants and also resistant plants can be discarded (missings). The efficiency of this seedling test will be discussed