On the basis of these results, we can assume that olive trees have undergone a different selection/domestication process in the insular and mainland regions. The degree of differentiation between oleasters and cultivated trees on the islands suggests that all cultivars have been introduced into these regions from the outside, while the Umbrian cultivars have originated either by selection from local oleasters or by direct introduction from other regions.
The construction of a databank based on a large number of samples, which is available at URL http://www.olimonovarietali.it, has contributed to the reduction of the variable effects involved in the oil production process. Knowledge of the chemical and sensory profiles of the Italian monovarietal olive oils could start a certification process of these oils, thus giving greater guarantees about their origin.
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 prohferation phases, the shoots with obvate leaf shape which occurred among the shoots with normal lanceolate or intermediate leaf shape.Genetic improvement of the olive tree by breeding has had only limited success (Lavee et al. 1986), principally because knowledge of the genetic basis and heritability of economic characters is limited. It is difficult to determine the genetic control of these characters because of the high genetic variability, the long-term juvenile phase and the outcrossing habit of the species to the widespread occurrence of self-incompatibility. The heterozygous nature of olives results in highly variable offspring which differ from the parents in many characters, making it difficult and tedious to select plants with good quahty. However, high heterozygosity could be an advantage when attempts are made to improve characters by induced mutations without substantially affecting the rest of the genotype of the new cultivar.The induction of genetic variability in high-value agronomic olive cultivars by mutagenesis has been the main goal of many researchers in an attempt to obtain trees suitable for planting at high density in ohve groves. Roselh and Donini (1982) obtained a compact 'Ascolana tenera' mutant by this approach but it was not of agronomic value. Petruccioh et al. (1974) isolated numerous somatic mutants from the cultivars 'Leccino' and 'Erantoio'. Only three were particularly interesting because of their compact or dwarf vegetative habit. Later, Pannelli et al. (1990Pannelli et al. ( , 1992, characterized those plants and three have been named EC (from 'Erantoio') and LC (from 'Leccino') for their compact habit, and LD (from 'Leccino') because it was dwarf. The cropping capacity of EC was low, while LC cropped regularly. Both mutants produced some fruits of large size, almost double that of normal ones (with higher frequency in LC than EC). LD flowered regularly, but fruit set was reduced by the lack of pollen in the environment during the late blossoming (1-2 w...
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