STRATEGY FOR ROSE BREEDING IN HUMID TROPICS
Allen (1970) reported that thereto direct link between powdery mildew resistance and leaf content of anthocyaniciins. tgo such relationship was rioted with anthocyanin content.
Field resistance to Black Spot Disease (Diplocarpon rosae) depends not only on inherent tissue resistance, but also on conditions of growth, structural and environmental (Saunders, 1966). Resistance is apparently determined by polygenic factors that are inherited independently. According to Steward and Semeniuk (1959) the hybrid polygenic character of modern roses makes the segregation of genetic characters so complex that it is impossible to describe any clear example of Mendelian inheritance of resistance to Black Spot and the inheritance of such resistance is, therefore. nearly impossible to predict. Successful breeding for resistance might be possible by using the more resistant species, such as Rosa roirluniaina, and the cultivars of Rasa that possess some inherent stability of genetic material during mitosis and moods. “Allgold” miltivar is one of the few highly resistant roses, but it is not immune. Wylie (1955) concludes that the only way to reach true disease immunity will be from inter-species hybridization, although polyploids and mutations may prove useful.
This would be based on crossing the Noisette “Camargue” (Syn. “General Lainargue”) with It. elinophylla Thory (Syn R. nrcoluernta Snob.). Dr. B. P. has described “Camargue” as “one of the best climbers for the plains” and R clinophylla as “the wild rose of the tropical tracts of India”. The first generation should yield heat tolerant climbers and these, when selfed or back crossed on to “Camargue” would yield recurrent flowered chinthem. Back-crossed with such motile diploids as “Trier” and “Thisbe” the F2 progeny would include dwarf bedding roses suited to the tropical lowlands (Anonymous, 1977).
MUTATION BREEDING
Nlutations are sudden heritable changes in the characteristics of an orgthism. It is a pennanent genetic change, which in Iran produces new form. It may be chromosomal, cytoplasmic, or gene mutations. In nature the rate of spontaneous mutation is in very low frequency. In most of the case it is usually recessive, deleterious, random, recurrent in the occurrence and shows pleiotropy due to mutation in closely linked genes Bud sport and spontaneous mutahon has played an important role in origin and evolutinn of many new and novel varieties of rose. A large number of new varieties evolved as a bud sports or spontaneous mutation in India and abroad which have been reported from time to timo
Roses are very suitable plants for mutation breeding as it plays an important role in producing novelties in flower color and form. 13i-colour and striped roses developed by this method are very beautiful and added new dimensions among rose cultivars. These value added new roses are in great demand. (Gowda Narayana and Shobha, 1990).
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