Nematode resistance of rape-radish chromosome addition lines

Oilseed radish is resistant to the beet cyst nematode ( Heterodera schachtii Schmidt), interrupting the life cycle of this sedentary pathogen by blocking feeding cell development in the root. A complete set of nine disomic rape-radish chromosome additions, a to i , derived from a susceptible rapeseed parent as recipient and a resistant radish as chromosome donor, was assayed for nematode resistance. The addition line d exhibited the resistance level of the radish parent, confirming previous results that radish chromosome d carries a dominant gene, Hs1 Rph , for nematode resistance. It was investigated if Hs1 Rph is effective against a further important sedentary parasite, the northern root-knot nematode Meloidogyne hapla . The set of chromosome addition lines and the parents, rape and radish, were inoculated with second-stage juveniles (J2) of M. hapla and the plant reaction was evaluated by counting the number of egg masses per root system. By contrast to the situation in H. schachtii , the radish parent as well as addition line d showed no resistance against M. hapla and was even more susceptible than rape. It was concluded that the resistance gene Hs1 Rph , which inhibits syncytium development of H. schachtii , is ineffective against M. hapla , a nematode inducing giant cell formation. Most added radish chromosomes significantly changed the number of egg masses in the recipient rape towards higher susceptibility. Two chromosomes enhanced the egg mass number beyond that of the chromosome donor radish. However, one radish chromosome decreased the egg mass production in the corresponding addition line below that in rape. This wide range of effects of the individual radish chromosomes in the rape background indicates a quantitative inheritance of host suitability to M. hapla and a complex interaction between the pathogen and radish.