Fusarium resistance in Gladiolus: selection in seedling populations

A test to select Fusarium resistant seedlings of Gladiolus is described. Seedlings of 37 populations, obtained from an incomplete diallel between eight parents with different levels of Fusarium resistance, were used. Significant differences in Fusarium infection between and within populations were detected. Most of the descendants selected had a resistant G. dalenii genotype as one of the parents. The resistance level of the parents was associated with the general combining ability for Fusarium resistance based on the seedling test. Implications for resistance breeding are discussed

Breeding for resistance to Fusarium oxysporum in flower bulbs

Cultivation of the major flower bulb crops, e.g., lily, narcissus, gladiolus and tulip, is threatened by the soil-borne fungus Fusarium oxysporum. Fusarium infected bulb lots have lower yields and cause significant problems for bulb export and cut flower production. Besides cultivation practices and chemical protection, resistant cultivars can play an important role in preventing this disease. To breed Fusarium resistant cultivars, screening and selection tests have to be developed and genetic variation in the host and in the pathogen determined. Information about the inheritance can be helpful in selecting the parents with the best breeding value for Fusarium resistance. Clonal screening tests under standardized conditions (e.g., concerning temperature, inoculum concentration and duration of the test) are developed for lily, narcissus, gladiolus and tulip using artificially infested soil or bulbs. By using a clone of a genotype, levels of resistance can be determined accurately. Severity of the disease is mainly observed by using disease ratings or the percentage of diseased bulbs. Partial resistance to Fusarium is present in all four crops. In Narcissus and Gladiolus even species with absolute resistance were identified. Resistant species are used in interspecific breeding programmes with commercial cultivars. Variation in virulence of Fusarium was investigated for f.sp. lilii, f.sp. gladioli and f.sp. narcissi. In all these formae speciales indications for race-formation were observed. Comparison of different sizes of bulbs within genotypes showed that screening immature bulbs is possible. Tests of individual plants in the seedling stage also gave promising results for a more efficient selection system. The use of indirect selection by molecular markers was investigated in the lily-Fusarium interaction. Inheritance of resistance in all four crops was mainly of a polygenic nature. Breeding values of parents determined after diallel analysis correlated well with resistance levels determined in clonal tests

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

Segregation of Fusarium resistance in an interspecific cross between Lilium longiflorum and Lilium dauricum

Using interspecific hybridisation techniques, a resistant accession of L. dauricum (section Sinomartagon), was crossed with the susceptible L. longiflorum cultivars 'Gelria' and 'Flevo' (section Leucolirion). The progeny was tested for Fusarium resistance in a standardised scale-bulblet assay. Both resistant and susceptible descendants were found, indicating that the resistance was passed from the resistant parent to the progeny and that the resistance segregates. The level of the most resistant descendants equalled that of the resistant parent. It is concluded that L. dauricum can be used as a source of Fusarium resistance in interspecific crosses with L. longiflorum