Resting Spore of Plasmodiophora brassicae Proliferates only in the Callus of Clubroot Disease-Susceptible Turnip but Increases the PAL Activity in the Callus of Clubroot Disease-Resistant Turnip

Abstract

The calluses were induced from turnips, Brassicae campestris L. which were susceptible and resistant to Plasmodiophora brassicae in Murashige-Skoog's agar medium supplemented with 1.0 ppm 6-benzylaminopurine and 0.5 ppm α - naphthalene acetic acid. When a 10 μ1 water suspension containing 104 resting spores of P. brassicae was placed on the surface of the calluses, about 3 × 105 zoosporangium-like spheroids (SLS) were recovered from the susceptible calluses after 24 h of the treatment but no SLS was found in the resistant callus. On 6th day after the treatment, the SLS increased to about 4 × 106 in the susceptible callus. Upon inoculation of resistant callus with 104 resting spores, the phenylalanine ammonia lyase (PAL) activity increased about 4-fold after 20 h, however, such increase was not observed in the susceptible callus during the same period. The constitutive PAL activity of susceptible callus was roughly one 6th of that of resistant callus.