Agrobacterium rhizogenes . [Descriptions of Fungi and Bacteria

Abstract

Abstract A description is provided for Agrobacterium rhizogenes . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Maluspumila, Rosa spp., Rubus spp. A further 23 hosts representing 22 genera in 12 families are listed by Elliott (31: 105), p. 4. DISEASE: Hairy root of apple, pear, raspberry, and rose. Symptoms on apple consist of a very large number of small roots protruding from the stems or roots or from localized hard swellings at graft unions, or in roses at the ends of cuttings or at disbud scars (43: 487). These malformations may be fleshy at first but eventually become fibrous. Distinguished from crown gall caused by A. tumefaciens , by the production of fibrous roots on the surface of the gall. Apple trees inoculated with A. rhizogenes became stunted whilst trees infected with A. tumefaciens were not significantly smaller than controls (38: 527). Inoculation of apple trees with mixed cultures of the two species resulted in gall formations showing intergrading features characteristic of both diseases (11: 461). The two pathogens also produce distinct symptoms on rose (43: 487). GEOGRAPHICAL DISTRIBUTION: Widely distributed in apple nurseries and orchards in the U.S.A. Also recorded on rose in Calif, and Texas (43: 487; 19: 348; 16: 613). Outsize the U.S.A., there are few definite records. There are reports from Japan (Fujioka, 32: 278, p. 12), Bulgaria (13: 493), France (43: 2639), and two unconfirmed from Italy (15: 774; 25: 493). Records given by Hedgecock ( Bull. Bur. Pl. Ind. U.S. Dep. Agric . 186: 12, 1910) of the occurrence of the pathogen in Canada, Germany and the Netherlands have not been confirmed and are probably incorrect (CMI Map 140). TRANSMISSION: Agrobacterium rhizogenes is exclusively a wound pathogen (13: 776), and is readily disseminated on nursery stock which may become infected from soil or by tools contaminated with the pathogen when cuttings or grafts are made. Infection is also spread in apple stocks by insects which eat the galls and other underground parts. On rose, the bacteria may penetrate roots through injuries causes by the root-lesion nematode, Pratylenchus vulnus (43, 481). Survival in steamed or untreated soil for more than one year has been demonstrated, and virulence has been maintained in culture for over 19 years (40: 513).