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L. angustifolius genotypes susceptible to Fusarium root rot and wilt can be grown in new lupin land without disease symptoms, however, lupin root rot and wilt pathogens build up during repeated cropping of susceptible lupins in the same field. After four lupin crops symptoms of root rot and wilt began in an inhomogeneous pattern over the field, and after another three lupin crops susceptible lupins are destroyed before flowering homogeneously over the field and caused total crop failure. The dominating pathogens isolated from diseased lupins with root rot and wilt symptoms in this field are in descending order F. oxisporum, F. solani, F. culmorum, and F. avenaceum, the latter only being isolated from young autumn sown plants. A core collection of lupin genotypes was studied for susceptibility in this field. Varieties from Poland and Australia were severely damaged by Fusarium wilt whereas varieties from Russia, Bellarussia, Germany and Denmark appeared to have almost normal growth with a good pod set. The genetic control of resistance to Fusarium root rot and wilt were studied in F1, F2 and F3 hybrid populations between resistant and susceptible genotypes. F1, and single pod descent F2 and F3 hybrid populations showed that wilt resistant genotypes have two dominant non-allelic resistance genes. We call this gene Relation to Fusarium oxisporum (Rfo1,Rfo2). Susceptible genotypes have either two wild genes (++ ++) or one wild and one dominant resistant gene (++ Rfo2Rfo2 , or Rfo1Rfo1 ++). Crossing ‘++ Rfo2Rfo2’ to ‘Rfo1Rfo1 ++’ segregates in 9:7 resistant to susceptible in F2, the same segregation was observed by crossing ‘Rfo1Rfo1 Rfo2 Rfo2’ to ‘++ ++’. Segregation pattern in F1, F2 and F3 populations revealed three non-allelic dominant resistance genes to Fusarium root rot. Genotypes possessing 2 of these 3 genes are resistant. The presence of 3 non-allelic resistance genes gives the option in future to create varieties with 3 resistance genes, which might increase the stability of the Fusarium resistance compared to genotypes only possessing 2 of the 3 resistance genes. It is recommended to breed Fusarium root rot and wilt resistant varieties to avoid problems in new lupin growing areas despite resistant varieties can be grown in the first years. |
