Submitted to: Journal of Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 18, 1996
Publication Date: N/A
Interpretive Summary: Smaller pear trees that can be used in modern intensive orchard systems are needed. These must have fruit of proven quality desired by consumers and commercial marketers of fruit. Thus, it is desirable to change tree growth characteristics without affecting fruit. Shoots of four pear varieties growing in tissue culture were treated with gamma rays to cause mutations. The shoots were then multiplied in tissue culture and rooted. The resulting trees were planted in an orchard to select trees with more compact growth habits. After five to seven years in the orchard, a small number of trees were identified that had the desirable compact growth habits sought. Producing these compact trees was accomplished in fewer years and at considerably less cost than would have been required to produce such trees in a breeding program. These trees are now being evaluated for the quality and quantity of fruit produced.
In vitro shoots of four pear (Pyrus communis L.) cultivars, 'Conference', 'Doyenn¿ d'Hiver', 'Passe Crassane' and 'Bartlett', were irradiated with gamma rays (3.5 Gy). Around 1000 microcuttings of each cultivar were treated. After three subcultures, microcuttings from both the irradiated shoots and additional non-irradiated shoots were rooted; the plants obtained were used to establish a survey orchard in Ostellato (Ferrara), Italy. In the first 2 years of growth in the field trees were observed for growth and survival, but no data were collected. Then field surveys were executed to describe the population and identify mutants for vegetative traits. Trees that showed phenotypic evidence of vegetative growth characteristics more desirable than those shown by the overall population and by control plants were selected and measured for three years. Traits used for selection were reduced tree size, wide branch angle and short internodes. Frequencies of variants with compact habit varied with cultivars from 0.5% to 2.7% of the irradiated trees. Effect of mutagenic treatment and efficacy of the selection methods used are discussed.