Isolation of paraquat-tolerant mutants from tomato cell cultures.

Tomato callus clones selected for the ability to grow at paraquat concentrations lethal to wild-type cells were found at an approximate frequency of 5×10(-8) per viable cell. Diploid plants were regenerated from nine of the nineteen paraquat-tolerant callus clones isolated. Although some of these plants appeared normal, others had altered morphology and reduced vigor and fertility. New callus cultures initiated from these regenerated plants typically had at least a 30-fold increase over the wild type in tolerance to paraquat. Tests on callus from sexual progeny showed that the paraquat-tolerant phenotypes of clones PQT(4), PQT(6), and probably also PQT(13) resulted from dominant nuclear mutations, but the number of loci involved is not yet known. Paraquat spray experiments indicated that slight paraquat-tolerance was expressed at the plant level in PQT(13), but not in any of the other clones tested.