Characterisation of alien chromosomes in monosomic additions of Beta

Wild Beta species of the section Procumbentes carry genes for several valuable agronomical traits, and are considered to be of interest for the breeding of cultivated beet (B. vulgaris subsp. vulgaris). In spite of several barriers, it was shown that gene transfer from B . procumbens into sugar beet is possible. In such studies monosomic additions (2n=19) in B. vulgaris, harbouring different individual chromosomes of the wild species, play a very important role. To select the monosomic addition plants, an extensive number of different B.procumbens or B. patellaris derived monosomic addition families were screened, using repetitive DNA sequences and a squash-blot hybridisation procedure. The extra chromosomes of the monosomic additions were identified with the aid of DNA fingerprinting. In B . procumbens derived monosomic additions, the chromosome numbers of two additions had to be renamed. Seventyfive anonymous B.patellaris derived monosomic additions were grouped in nine different groups, many of them with two sub-groups. The. morphological characteristics of the plants of the nine different groups of monosomic additions of B. patellaris were described and comparisons were made between these groups and the monosomic additions of B.procumbens. Chromosome characterisation also was studied using fluorescence in situ hybridisation on mitotic chromosomes and extended DNA fibres of a series of monosomic additions of B. procumbens. The monosomic additions were evaluated in greenhouse tests for resistance to the beet cyst nematode (Heterodera schachtii), Cercospora beticola, Polymyxa betae and BNYVV. These experiments permitted the localisation of major genes for resistance on specific chromosomes, and the study of some quantitative effects.