CLASSICAL BREEDING OF ROSA RUGOSA ROSES AND IN VITRO CULTIVATION OF IMMATURE EMBRYOS AS AN EXPANDED RESOURCE FOR SELECTION

The main criteria for the suitability of rose cultivars in northern regions are good winter hardiness, high resistance to fungal diseases, and high quality of flowers in conditions of wet and cool summer and autumn. As to some extent possessing these requirements, Rosa rugosa Thunb. shrub roses have been involved in the breeding programme by D. Rieksta. The 12 obtained cultivars meet these requirements; they do not need winter cover, form bushes 1.2–1.5m high, have a continuous flowering period, and their flower colour range from white (‘Parsla’) through rosy with a white centre (‘Abelzieds’) to dark reddish-purple (‘Zilga’). However, traditional breeding methods have not succeeded in producing either recurrently blooming roses with yellow or bright red flowers or climbing-rose varieties. To expand the breeding programme, we started to develop sterile embryo culture. In vitro methods have been used mainly for hybrid tea roses, more rarely for miniroses, and have been aimed at initiating somatic embryogenesis in callus cultures. There is scarce information concerning the cultivation conditions of immature rose embryos. This study has been carried out in two directions: (1) development of callus cultures with initiation of somatic embryos and (2) elaboration of technology to get fertile seeds in vitro from immature embryos isolated in early stages after incompatible crosses. As a result, two crossings were introduced in vitro with the last technology.

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