A Root-Specific Decay of Grapevine Caused byAgrobacterium tumefaciensandA. radiobacterBiovar 3

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Abstract
Tumorigenic (T) and nontumorigenic (NT) biovar 3 strains of Agrobacterium tumefaciens and A. radiobacter, respectively, were isolate from dark, sunken lesions on roots of grapevines grown in a commercial nursery. Roots of the grape cultivars Concord [Vitis labrusca] and Pinot Chadonnay (V. vinifera] decayed after inoculations with T and NT biovar 3 strains. Thirty-five strains of biovar 3 from several geographic areas worldwide reacted identically. Decay was restricted to the roots of grapes, whereas tumors were incited by T strains on grape shoots and on other hosts. No decay resulted when T and NT strains ofbiovars 1 and 2 were inoculated to grap roots. In addition, none of the strains decayed bean or sunflower roots. Root decay may provide sites for entrance of Agrobacterium into the grape vascular system and may cause detrimental effects on root development and vine growth.