GROWTH OF ALBUGO-CANDIDA IN LEAF CALLUS-CULTURES OF BRASSICA-RAPA

The present study provides evidence that Albugo candida race 7V develo ps haustorial connections with callus cells of its host, Brassica rapa . Leaf callus tissue was cultured on Murashige and Skoog's medium supp lemented with the growth regulators alpha-naphthaleneacetic acid (1 mg L(-1)) and benzylaminopurine (1 mg L(-1)). Except for a slight delay in the formation of haustoria in the dark, the development of the fung us was not affected by illumination. The formation of oospores of the fungus was favoured over that of zoosporangia. Both mature and parthen ogenetic-like oospores were observed in the callus tissues; germinatio n by germ tube occurred only in parthenogenetic-like oospores. The est ablishment of A. candida and B. rapa in dual culture may provide a sel ection system for breeding genotypes resistant to white rust.