Protoplast culture of deciduous fruit trees

Abstract

In deciduous fruit trees, parasexual breeding methods by using their protoplasts will be very beneficial, owing to their heterozygosity in genotype and long juvenile period. To date, however, only a few experimental results of protoplast culture have been reported in these tree species. Protoplasts have been isolated in some species of Malus, Pyrus and Prunus by the treatment for various tissues or cells with enzyme solutions fundamentally containing both pectinase and cellulase, but the yields and viabilities of the obtained protoplasts varied widely relating to the conditions of sources and treatments. At the first step of protoplast culture, various supplements and relatively high osmotic pressure of media were required for cell-wall regeneration and initiation of cell division. Cell colonies were then formed as a result of continuous cell divisions under the reduced osmotic pressure, and they could relatively easily be proliferated into calli. Morphogenesis from protoplast-derived cells has been reported only in a few cases, namely embryoid-like structures in Malus pumila, shoots in Pyrus communis var. pyraster, and shoots and roots in Prunus avium × pseudocerasus. With the object of inducing somatic hybrid plants, protoplast fusions have been investigated in Malus pumila. Heterokaryons, which could be identified with chloroplasts, exhibited cell divisions and formed calli, but they have not yet differentiated any embryoid or organ.