title: The Hypersensitivity Reaction of Tomatoes Resistant to Meloidogyne incognita: Reversal by Cytokinins.
abstract: Initiation of larval growth, induction of cell necrosis, and gall formation in the host were measured as criteria of resistance or susceptibility of tomato seedlings to the root-knot nematode, Meloidogyne incognita (Kofoid &White) Chitwood. Seedlings grown at 27 C on water agar containing additions were scored 3 or 4 days after infection.In the absence of exogenous plant growth regulatory substances, approximately 73% of larvae that entered roots of susceptible plants showed growth, none induced necrosis and nearly all induced gall formation. In roots of a resistant variety, only 4% of the larvae grew, 88% induced necrosis of host cells, and only 29% induced galls. Exogenously supplied cytokinins shifted the response of the resistant plants toward the susceptible reaction. Exogenous kinetin at 0.4 and 0.8 micromolar allowed 55 and 57% of the nematodes to grow, reduced the incidence of necrosis to 32 and 31%, and increased gall formation to 73 and 65%. Three additional cytokinins, Zeatin, 6-(gamma,gamma-dimethylallylamino)purine, and 6-benzylaminopurine produced effects similar to kinetin. Exogenous indoleacetic acid, gibberellic acid, adenine, guanine, uracil, thymine, cytidine, and 6-methylaminopurine neither increased the percentage of larvae which grew nor decreased the extent of host cell necrosis.
authors.forename: V H
authors.initials: VH
authors.lastname: Dropkin
authors.forename: J P
authors.initials: JP
authors.lastname: Helgeson
authors.forename: C D
authors.initials: CD
authors.lastname: Upper