ISHS Acta Horticulturae 403: International Symposium on Cultivar Improvement of Horticultural Crops. Part 2: Fruit Crops
PRELIMINARY STUDIES ON THE GENETIC CHARACTERISTICS OF FRUIT PLANTS |
| Authors: | J. Shixi, W. Luping, L. Baojing |
| Abstract:
Studying genetic characteristics of different groups of living bodies is a researching field of a new branch of hereditism science comparative genetics. Since the genetic science had been originated. geneticists researched and unravelled lots of biological phenomena and genetic rules in common, among various kind of animals and plants, such as segregation recombination of genes, linkage, crossing over, almost all complex cytological process of meiosis, common genetic code, crossing over, almost all complex cytological process of meiosis, common genetic code, advanced variation of genetic materials, mutation and chromosomal variation etc., But they neglected to some extent, the genetic characteristics among different groups of animals and plants, which have been formed over the long evolutional period. The genetic characteristics of one groups of organisms differs with others owing to their growth form, developmental pattern, lifespan, fertilizer, mode of reproduction, seeding medium and other functional characters correlated with genetic system. But as Huxley (1942)[2] has indicated. " comparative genetics and comparative evolution are for the most part sciences for the future, and most statements concerning them at present be largely hypothetical". Stebbins (1975)[5] advocated that" the gathering together of facts and opinions on these subjects is desirable at this early date. even if only to form a basis for future discussion and for design of critical experiments". The characters and habits of fruit plants relative to genetic system have been compared and analyzed in the present paper, and proposals concerning several genetic characteristics of fruit plants have been put forward as well.
1.1 The reproductional ecotype of most fruit plants belong to the advanced group of evolution, their pollination rely on bees or other insects. Instead of seeds, fruits as a disperse medium attract the birds and beasts to disseminate their seeds. They belong to a group of angiosperm, since their relationship of structure and function between seeds and fruits are highly variable. Stebbins (1975)[5] denoted that "many more adaptive gene combinations are possible in plants which rely on animals for their vital reproductive function". Their diversity results from cooperative evolution of the fruit plants with pollinating and seeding animals over long historical period. 1.2 In fruit plants with larger size and longer life cycles, other factors favouring flexibility would have a correspondingly higher selection value. 1.3 Heterozygosis and lack of selection for constancy make the mutant rate of fruit plants higher than that of crop plants, Sturtevant (1973) and Shapiro (1983)[6] concluded that, since in all well established species most mutations would be harmful, selection would tend to lower the mutation rate through the ages in the genes of a species by establishing mutant genes which act as mutation suppressor. Gustafsson (1974)[1] studied spontaneous and induced mutation rate in three different barley cultivars. He concluded that, "the history of Golden barley and of other old varieties of cereals has included many generations of gene combinations reducing the mutation rate. The breaking up of these combinations by intervarietal hybridization is responsible for the increased mutation rates in the newer varieties." Fruit breeding contains, in general the breaking up of combinations by gene recombination, but lacking of selection for constancy. | |
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