Citrus is among the most important fruit crops worlstwide, and therefore the preservation and improvement of citrus germplasm is of the essence. Citrus breeders are often faced with the difficulty of distinguishing between new and existing cultivars because of the ambiguous nature of morphological traits due to environmental influences and error in human judgement. The protection of new varieties is very important to the breeder. New varieties cannot be patented in South Africa, but it can be protected by Plant Breeders' Rights, only if it is genetically distinguishable and significantly different economically from existing varieties. Cultivars in four genera (c. sinensis, C. paradisi, C. grandis and C. reticulata) included in the Citrus Improvement Programme (CIP) or cultivars awaiting recognition of Plant Breeders' Rights by the International Union for the Protection of New Plant Varieties (UPOV) were analyzed with Isoenzymes, Restriction Fragment Length Polymorphism (RFLP) and Random Amplified Polymorphic DNA (RAPD). Five enzyme systems (PGM, PGI, MDH, GOT and IDH) were analyzed and founded to be suitable for grouping together cultivars belonging to the same genera. It was not suited for routine discrimination of cultivars in a particular genus. RFLP studies were conducted on five grapefruit cultivars, using cDNA clones from a genomic library of Rough Lemon. RFLP studies were valuable for the discrimination of closely related cultivars which probably originated from a common ancestor by bud mutations. This technique was, however, abandoned due to its biohazardous nature and replaced by the PeR-based Random Amplified Polymorphic DNA. RAPDs are easy to perform and gave promisin& results which were exploited to reveal polymorphisms between cultivars within the various groups. Although the interpretation of data produced by this method is often suspicious, it is the best method currently available for cultivar identification. It can playa complementary role in the protection of new varieties when classical morphological interpretation of differences is not capable of determining sufficient distinctness for the awarding of Plant Breeders' Rights.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:rhodes/vital:4022 |
| Date | January 1995 |
| Creators | Carstens, Karin |
| Publisher | Rhodes University, Faculty of Science, Biochemistry, Microbiology and Biotechnology |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis, Masters, MSc |
| Format | 101 p., pdf |
| Rights | Carstens, Karin |
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