Isolation of triploid and tetraploid olive (Olea europaea L.) plants from mixoploid cv 'Frantoio' and 'Leccino' mutants by in vivo and in vitro selection.

This paper reports a procedure for isolating triploid and tetraploid olive plants, which have not been produced before either artificially or in nature. These polyploids were isolated from two mixoploid somatic mutants obtained earlier by treating 'Frantoio' and 'Leccino' plantlets with gamma radiation. The mixoploid mutants exhibit increased thickness-of leaf, stem and root tissues, short internodes, a modified leaf lamina shape and a strong resistance to Spilocaea oleagina (Cast.) Hugh. In addition, they produce a mixture of normal drupes and some abnormally large ones, almost twice normal size. The variation in the nuclear DNA content of the mixoploid mutants is closely correlated with variation in their pollen size, crop capacity and the production of large fruit. Triploid genotypes with 69 chromosomes were isolated by germinating the seeds of these large fruits, collected from both the mixoploid mutants. Tetraploid plantlets, with 92 chromosomes, were obtained from cv. 'Frantoio' by selecting in vitro, during several proliferation phases, the shoots with obvate leaf shape which occurred among the shoots with normal lanceolate or intermediate leaf shape.