Reactions to a verticillium dahliae phytotoxin in tissue cultures derived from susceptible and tolerant potato

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Tissue cultures of potat ( Solanum tuberosum L.) have been used successfully to determine host-specific properties of a Verticillium dahliae phytotoxin (Vd toxin) which was partially purified from culture fluids of a fungal isolate pathogenic for potato. The Vd toxin, at concentrations of 5 μg/ml and above, significantly reduced ( P = 0.05) the viability of suspension cells from the disease susceptible cvs. Blanka and Russet-Burbank but not those obtained from the tolerant cv. Alpha. The lethal effect was concentration dependent ( P = 0.01) and increased with time, but cells of cv. Alpha were not killed by any concentration tested. The differential effect on root cultures was similar. The fresh weight of sterile plantlets from cv. Russet-Burbank was markedly reduced ( P = 0.001), compared to that of cv. Alpha, after 30 days in the presence of Vd toxin. A bioassay test was developed, based on the inhibition of growth of cultured potato roots, to assess the relationship between the Vd toxin and the stunting effect in V. dahliae-infected plants. The toxin killed 95% of susceptible root tips (cv. Blanka), while roots from the tolerant cvs. (Desiree and Alpha) were unaffected ( P = 0.01). However, when the toxin was incubated with protoplasts or calli of the susceptible cv. Blanka or diseass tolerant cvs. Alpha and Spunta, no difference was observed among the cultivars. The results indicate that bioassays using suspension cells, sterile plantlets or root cultures are comparable and reliable for the detection of Verticillium with tolerance.