ISHS Acta Horticulturae 579: II Balkan Symposium on Vegetables and Potatoes
THE EFFECTS OF CLONAL PROPAGATION ON THE GENETIC IMPROVEMENT OF POTATO |
| Author: | D.A. Fasoula |
| Keywords: | Honeycomb breeding, heterosis, inbred vigor, Solanum tuberosum. |
| Abstract:
The clonal propagation of potato offers important agronomic and genetic advantages, such as vigorous early growth, higher yields and the quick fixation of hybrid vigor. However, potato is characterized by nonadditive genetic variation and high inbreeding depression (Peloquin, 1995). Inbreeding depression was quantified in the F2s of two potato cultivars grown in the absence of interplant competition (90x90 cm) in Honeycomb trials, by the CV values of single plant yields. These values, which were very high (78 and 94%) and contrast sharply to respective low CV values of tomato and other crops, are associated with the clonal reproductive system of potato, which preserves a high load of deleterious genes. Deleterious genes can be concealed in repulsion or in coupling phase linkages. In case of repulsion phase linkages, gene fixation results in degeneration and hinders genetic advance through selection (Fasoula and Fasoula, 1997b). The ascertained lack of genetic improvement in potato, despite intensive breeding efforts, reflects the difficulty to remove deleterious genes from the potato germplasm. It also indicates that in potato, most deleterious genes are locked into repulsion phase linkages. In order to realize genetic improvement in clonally propagated crops, repulsion phase linkages must be converted into coupling. Consequently, nonadditive genetic variation will be converted into additive. It is demonstrated that the yield stasis in potato is related to its propagation by mitosis, which preserves repulsion phase linkages, and that the genetic gain through selection has two requirements: (1) Intralocus recombination, in order to convert trans- into cis-acting DNA sequences, and (2) gene fixation, in order to duplicate the cis-acting DNA sequences and bring about genetic advance through selection. Both actions presuppose sexual reproduction. The principles of the Honeycomb breeding and additional measures to overcome stagnation of genetic improvement in potato are detailed in Fasoula and Fasoula (2000). | |
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